Re: Dial face colouration

[Michael Ossipoff]

Alright, it isn't that simple, and I was closer to right the first time.

Find out by what factor (f) the sun will be brighter, due to higher
altitude, on the solstice, compared to the day of your experiment this
week.

Calculate the sun's zenith angle at summer solstice noon, and find the
cosine of that zenith angle.

Multiply that cosine by f, and find the angle (A) with a cosine equal to
that product.

Tip the color-sample card so that its normal is that many degrees away from
the sun.

Do that by subtracting the absolute value of the sun's declination on the
experiment day this week, from the complement of your latitude, to find the
sun's altitude on the noon of the experiment. Add or subtract A from that
altitude. Tip the color-sample card so that its north end is tipped up by
the complement of that angle.

In that way, the sunlight intensity on the color-sample card is what it
will be on the horizontal dial at summer solstice noon.

(unless I've made another error)

Michael Ossipoff

On Wed, Mar 1, 2017 at 10:27 PM, Michael Ossipoff 
wrote:

> What am I saying??
>
> You don't need the formula for the sun's brightness at different altitudes.
>
> You just need to tip the color-sample card, from the horizontal, toward
> the sun by an amount that's equal to the amount by which the
> summer-solstice deciination (23.44 degrees?) will be greater than the solar
> declination on the day of the experiment this week.
>
> That will give the color-sample card the same solar illumination that it
> will have at solstice noon.
>
> On Tue, Feb 28, 2017 at 5:09 PM, Steve Lelievre <
> steve.lelievre.can...@gmail.com> wrote:
>
>> John, thanks for the clarification, and your patience with my questions.
>>
>> All, I'm off to buy some photographic mattes to do experiements with.
>> This is all about having a horizontal dial face that is not too bright to
>> view even in the summer midday sun - so I'll go quiet now and report back
>> after the summer solstice.
>>
>> Steve
>>
>>
>>
>> On 2017-02-28 1:40 AM, John Lynes wrote:
>>
>> Hi Steve,
>> I'm sorry I've confused you.
>>
>> ...
>>
>> The take-home conclusion is that there is no single ideal reflectance for
>> the plate of a sundial.  It varies with the sky illuminance.  When Weber's
>> Law prevails, a reflectance of about 60 per cent is likely to be a safe bet.
>>
>>
>>
>> ---
>> https://lists.uni-koeln.de/mailman/listinfo/sundial
>>
>>
>>
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Michael Ossipoff]

What am I saying??

You don't need the formula for the sun's brightness at different altitudes.

You just need to tip the color-sample card, from the horizontal, toward the
sun by an amount that's equal to the amount by which the summer-solstice
deciination (23.44 degrees?) will be greater than the solar declination on
the day of the experiment this week.

That will give the color-sample card the same solar illumination that it
will have at solstice noon.

On Tue, Feb 28, 2017 at 5:09 PM, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> John, thanks for the clarification, and your patience with my questions.
>
> All, I'm off to buy some photographic mattes to do experiements with. This
> is all about having a horizontal dial face that is not too bright to view
> even in the summer midday sun - so I'll go quiet now and report back after
> the summer solstice.
>
> Steve
>
>
>
> On 2017-02-28 1:40 AM, John Lynes wrote:
>
> Hi Steve,
> I'm sorry I've confused you.
>
> ...
>
> The take-home conclusion is that there is no single ideal reflectance for
> the plate of a sundial.  It varies with the sky illuminance.  When Weber's
> Law prevails, a reflectance of about 60 per cent is likely to be a safe bet.
>
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Michael Ossipoff]

Well it's

1) How bright the dial face has to be for it to show a shadow when the sun
is as low as it can be at the sundial's mounting-location.

2) How un-bright does the dial need to be at noon on the summer solstice,
so that it won't be too bright to look at.

*As for #1*

, you can find that out whenever the sun is as low as the lowest it can get
at the sundial's mounting-location. And, if it isn't visible that low at
this time of year, due to obstacles like a tree or a house, then of course
you can go to a different location without that obstruction.  So you can
easily find the answer to #1 now.

So, at a location where the sun is visible as low in the sky as it can ever
get at the mounting-location, try brown, and, if the shadow isn't visible,
try light-brown, and then (dark, ordinary, and light) tan, and then yellow.

I rather doubt that it will require something as bright as yellow, unless
the dial will receive sunlight all the way to sunset.

Most likely some brown or tan will be light enough, depending on how low
the sun can be and still shine on the dial (which depends on the trees,
buildings and other obstructions in your yard.


*As for #2: *

One thing that you already know is that matte-black shows a shadow when the
sun is at its brightest, because it showed a shadow even during your recent
winter experiment. So matte-black will show a shadow at the solstice-noon
too.

Whatever shade of brown/tan/yellow is barely light enough to show a shadow
when the sun is at its lowest for your dial-location, that's a first thing
to try at summer-solstice noon.

But, if that's too bright at summer solstice noon, then you want to find
out how bright it's permissible for the dial to be, at summer solstice
noon, without being too bright.

For that, to be really sure, I agree that you have to wait for the summer
solstice. But you can get a good estimate now, if you have a formula for
sunlight intensity as a function of solar altitude:

Find out, from the formula, and from he noon solar altitudes now and at the
solstice, how many time more intense the sunlight is at summer-solstice
noon, as compared with noon on some day this week.

Find the sine of the sun's altitude at noon on some day this week. That's
also the cosine of the sun's distance from the dial-normal (perpendicular
line) at noon.

Multiply that cosine by the factor by which the sun will be brighter at
solstice-noon, as compared to that noon this week.

Find the angle whose cosine equals the result of that multiplication. Find
the difference between that angle and the sun's angle from the zenith on
this week's observing-day.

Tip your color-sample southward up from the horizontal, at noon, on this
week's observing-day, to get the sunshine-intensity that a horizontal
surface would receive on at summer-solstice noon.

So, with the color-sample tipped up southward at that angle, find the shade
that won't be too bright at solar noon on this week's observing day.

Hopefully there's a shade that is bright enough when the sun is at its
visible lowest at the dial-location, and still isn't too bright at solstice
noon (on a horizontal dial).

I'd bet that some brown or tan would be likely to meet both requirements.

Michael Ossipoff





On Tue, Feb 28, 2017 at 5:09 PM, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> John, thanks for the clarification, and your patience with my questions.
>
> All, I'm off to buy some photographic mattes to do experiements with. This
> is all about having a horizontal dial face that is not too bright to view
> even in the summer midday sun - so I'll go quiet now and report back after
> the summer solstice.
>
> Steve
>
>
>
> On 2017-02-28 1:40 AM, John Lynes wrote:
>
> Hi Steve,
> I'm sorry I've confused you.
>
> ...
>
> The take-home conclusion is that there is no single ideal reflectance for
> the plate of a sundial.  It varies with the sky illuminance.  When Weber's
> Law prevails, a reflectance of about 60 per cent is likely to be a safe bet.
>
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Steve Lelievre]

John, thanks for the clarification, and your patience with my questions.

All, I'm off to buy some photographic mattes to do experiements with. 
This is all about having a horizontal dial face that is not too bright 
to view even in the summer midday sun - so I'll go quiet now and report 
back after the summer solstice.


Steve



On 2017-02-28 1:40 AM, John Lynes wrote:

Hi Steve,
I'm sorry I've confused you.

...
The take-home conclusion is that there is no single ideal reflectance 
for the plate of a sundial.  It varies with the sky illuminance.  When 
Weber's Law prevails, a reflectance of about 60 per cent is likely to 
be a safe bet.


---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[John Lynes]

Hi Steve,
I'm sorry I've confused you.
The experiments reported in the 1941 UK paper were limited to illuminances
not exceeding 10 000 lux.  For that reason I had to admit that higher
illuminances might well point to a different conclusion.  I certainly did
not intend to suggest that reflected light should be limited to 6000 lumens
per square metre; simply that I have no experimental evidence handy for
illuminances exceeding 10 000 lux.

Weber's Law stated that if the background luminance is Lb and the stimulus
luminance is Ls, then the just-detectable luminance difference (Ls - Lb),
or in the case of a sundial (Lb - Ls), is proportional to Lb.  If Weber's
Law were correct then the perceived contrast of the shadow on a matt
sundial plate would be independent of the reflectance of the plate.

Although Weber's "Law" is approximately true, for many practical purposes,
over a wide range of values for Lb, it certainly fails under dim lighting
and under very bright lighting, when the "Weber fraction" (Lb - Ls)/Lb
rises.

Ideally for a sundial plate one would aim for the value of Lb which
minimises the Weber fraction.  Unfortunately there is little agreement over
the precise value of Lb at which this minimum occurs.  It is almost
certainly greater than 10 000 lumens per square meter of reflected light
but, as you have observed, well below the luminance of a white surface
under intense sunlight.

Once again I'm sorry to have confused you.  The take-home conclusion is
that there is no single ideal reflectance for the plate of a sundial.  It
varies with the sky illuminance.  When Weber's Law prevails, a reflectance
of about 60 per cent is likely to be a safe bet.

John Lynes
PS I'm away from my computer for the coming week, so will be out of touch
for some time.

On 28 February 2017 at 01:48, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> John,
>
> Will you clarify some things for me?
>
> You mention that 50 lumens per square foot is about 500 lux, and that the
> cited article recommends a limit of 60% reflectance for sky illuminance of
> up to 1,000 lumens per sq. ft. If I multiple all that out, it would appear
> to suggest a a limit of 6,000 lux of reflected light for comfortable
> viewing. Is that the case?
>
> Through Google, I found empirical rules for calculating the wattage of
> solar radiation reaching the ground, depending on season, altitude,
> declination, hour angle, and geographic elevation. I also found a
> conversation factor for converting sky illumination in watts per square
> metre to lux. Putting it all together, I get a figure of about 72,000 -
> 91,000 lux for the incident illumination,  at noon on the northern
> hemisphere summer solstice at sea level, depending on latitude (and valid
> for mid-latitudes only). Using the mid figure of 80,000 lux, if I want to
> limit the reflected light to 6,000 lux then the reflectivity has to be less
> than 22.5%, which corresponds to a lightness of only 3.5 on the Munsell
> scale.
>
> Does this conversion make sense, or don't things work like that?
>
> Of course, if we've gone out in midday sun, we should be wearing
> sunglasses and, again from the web, sunglasses reduce the visible light
> reaching our eyes by two thirds or more. If I factor that in, my Munsell
> value rises to 5.3. And, as you pointed out, when the sun isn't so high in
> the sky, we can tolerate a more reflectivity on our dial face.
>
> Thanks for any further comments or advice,
>
> Steve
>
> P.S. Based on what I've learned so far, I'm leaning towards using a
> material with a Munsell value of 6 or 7, which would correspond to the
> mid-grays, tans and browns that people have been suggesting may work in
> practice. It would be the number you mentioned but with the lightness
> notched down a little. My design latitude of 45N is a little further south
> than England (where the article's authors came from) and the summer sun is
> a tad brighter. As well, I reckon a suitable colour with a number of 6 or 7
> would look OK against a lawn, flowerbed or other greenery.
>
>
>
> On 2017-02-26 7:08 AM, John Lynes wrote:
>
> There is no single optimum reflectance for a flat dial face.  Obviously
> under dim sunlight the optimum reflectance would be 100 per cent,
> i.e.perfect white.
> Under intense sunlight, contrast sensitivity would be optimised for a
> lower value of reflectance.  Thousands of papers have been written on
> contrast sensitivity.  One classical study is "Brightness and contrast in
> illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram,
> Transactions of the Illuminating Engineering Society (London), Vol 6, No 3,
> pp 37-48 (1941).  This indicates that when the sky illuminance on a matt
> dial face is over about 50 lumens per square foot (about 500 lux) the
> optimum reflectance would be about 60 per cent (a light grey, about Munsell
> Value 8).  Below this illuminance (which would correspond to a solar
> altitude close to sunrise or sunset) the optimum 

Re: Dial face colouration

[Steve Lelievre]

John,

Will you clarify some things for me?

You mention that 50 lumens per square foot is about 500 lux, and that 
the cited article recommends a limit of 60% reflectance for sky 
illuminance of up to 1,000 lumens per sq. ft. If I multiple all that 
out, it would appear to suggest a a limit of 6,000 lux of reflected 
light for comfortable viewing. Is that the case?


Through Google, I found empirical rules for calculating the wattage of 
solar radiation reaching the ground, depending on season, altitude, 
declination, hour angle, and geographic elevation. I also found a 
conversation factor for converting sky illumination in watts per square 
metre to lux. Putting it all together, I get a figure of about 72,000 - 
91,000 lux for the incident illumination,  at noon on the northern 
hemisphere summer solstice at sea level, depending on latitude (and 
valid for mid-latitudes only). Using the mid figure of 80,000 lux, if I 
want to limit the reflected light to 6,000 lux then the reflectivity has 
to be less than 22.5%, which corresponds to a lightness of only 3.5 on 
the Munsell scale.


Does this conversion make sense, or don't things work like that?

Of course, if we've gone out in midday sun, we should be wearing 
sunglasses and, again from the web, sunglasses reduce the visible light 
reaching our eyes by two thirds or more. If I factor that in, my Munsell 
value rises to 5.3. And, as you pointed out, when the sun isn't so high 
in the sky, we can tolerate a more reflectivity on our dial face.


Thanks for any further comments or advice,

Steve

P.S. Based on what I've learned so far, I'm leaning towards using a 
material with a Munsell value of 6 or 7, which would correspond to the 
mid-grays, tans and browns that people have been suggesting may work in 
practice. It would be the number you mentioned but with the lightness 
notched down a little. My design latitude of 45N is a little further 
south than England (where the article's authors came from) and the 
summer sun is a tad brighter. As well, I reckon a suitable colour with a 
number of 6 or 7 would look OK against a lawn, flowerbed or other greenery.




On 2017-02-26 7:08 AM, John Lynes wrote:
There is no single optimum reflectance for a flat dial face.  
Obviously under dim sunlight the optimum reflectance would be 100 per 
cent, i.e.perfect white.
Under intense sunlight, contrast sensitivity would be optimised for a 
lower value of reflectance.  Thousands of papers have been written on 
contrast sensitivity.  One classical study is "Brightness and contrast 
in illuminating engineering" by RG Hopkinson, WR Stevens and JM 
Waldram, Transactions of the Illuminating Engineering Society 
(London), Vol 6, No 3, pp 37-48 (1941). This indicates that when the 
sky illuminance on a matt dial face is over about 50 lumens per square 
foot (about 500 lux) the optimum reflectance would be about 60 per 
cent (a light grey, about Munsell Value 8).  Below this illuminance 
(which would correspond to a solar altitude close to sunrise or 
sunset) the optimum reflectance would rise quite sharply.
Note however that the maximum sky illuminance considered by the 
authors was 1000 lumens per square foot (corresponding to a solar 
altitude of about 20 degrees).  Higher illuminances might further 
reduce the optimum reflectance.

John Lynes


---
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Re: Dial face colouration

[koolish]

18% gray is used because that was thought to be the average
reflectance of photographic subjects.

- Original Message -
From:
 "Patrick Vyvyan" <patrickvyv...@gmail.com>

To:
"John Lynes" <jly...@iee.org>
Cc:
"sundial list" <sundial@uni-koeln.de>
Sent:
Sun, 26 Feb 2017 13:01:10 -0300
Subject:
Re: Dial face colouration

When taking light meter readings for photography, it is common to use
an 18% grey card in place of the object which will actually be
photographed. This is generally considered to give a reading which
will accurately balance light and dark.

See: https://en.wikipedia.org/wiki/Gray_card [1]

Might be worth examining as an ideal tone for a sundial?

Patrick Vyvyan

Presidente

Corporación Cultural de Putaendo

On 26 February 2017 at 12:08, John Lynes <jly...@iee.org [2]>
 wrote:
There is no single optimum reflectance for a flat dial face. 
Obviously under dim sunlight the optimum reflectance would be 100 per
cent, i.e.perfect white.
Under intense sunlight, contrast sensitivity would be optimised for a
lower value of reflectance.  Thousands of papers have been written on
contrast sensitivity.  One classical study is "Brightness and
contrast in illuminating engineering" by RG Hopkinson, WR Stevens and
JM Waldram, Transactions of the Illuminating Engineering Society
(London), Vol 6, No 3, pp 37-48 (1941).  This indicates that when the
sky illuminance on a matt dial face is over about 50 lumens per square
foot (about 500 lux) the optimum reflectance would be about 60 per
cent (a light grey, about Munsell Value 8).  Below this illuminance
(which would correspond to a solar altitude close to sunrise or
sunset) the optimum reflectance would rise quite sharply.
Note however that the maximum sky illuminance considered by the
authors was 1000 lumens per square foot (corresponding to a solar
altitude of about 20 degrees).  Higher illuminances might further
reduce the optimum reflectance.
John Lynes

On 26 February 2017 at 02:25, Michael Ossipoff <email9648...@gmail.com
[3]>
 wrote:

It seems to me that Steve's question has been mostly disregarded
rather than answered.

Not having experience with translucent dial-faces, I didn't know about
their lack of accuracy, and I certainly can't disagree with what two
people have said about that. 

It means that the advantage of a translucent dial, for omnidirectional
reading, comes with a disadvantage of less precise accuracy.

But of course a high-mounted dial intended for relatively distant
reading might not be as concerned with fine accuracy as with
omnidirectional viewing. And so translucent dials for all-directions
viewing certainly aren't ruled-out.

Steve's main question was about the choice of dial-face hue,
saturation and brilliance, for easy and safe dial-reading. It seems to
me that Steve's question has been mostly disregarded and discounted
rather than answered.

I lied. 

I said that I can't speak from experience on that matter.

But my experience with a few paper-on-cardboard tablet-dials is
sufficient to say this:

From my experience, I can say that you definitely don't want a white
dial-face.

As I said, my first dial had a white dial-face. After that, I switched
to brown, which was a big improvement in usability. 

I suggest brown instead of white.

Someone implied that, the more contrast (between light and shadow),
the better. Not so, when the dial-face is too white to look at in
bright sunlight.

As for gray: Gray reflects the visible wavelengths in a relatively
equal mix, resulting in no perceived hue. If some hues are (at least
relatively) to be avoided, then obviously gray isn't what you want.

At each end of the visible spectrum, there is, of course, radiation
that isn't visible.

Infrared (IR) and ultraviolet (UV).

 One possible disadvantage of that is that, when you don't perceive
it or its intensity, then of course you could conceivably get a
dangerous amount (accutely or cumulatively) without any perception of
it.

For example, never look at the sun when, due to a haze, or due to the
sun being low in the sky, the sun doesn't look bright. You don't have
any perception of how ingtense the UV or IR is. It could burn your eye
without any feeling of discomfort. (I don't know which of those is
more dangerous, but there have been official warnings to never look at
the sun when it seems less bright due to haze or low altitude.)

Aside from that, there's been evidence that, when people spend a lot
of time outdoors, in bright sunny climate, then many years of exposure
to the bright blue light can cause some long-term cumulative damage.
So maybe blue isn't the most desirable hue.

Yellow, beings the complement of blue, looks yellow because it absorbs
blue, removes blue from the light that it reflects.

Also, yellow isn't particularly close to either end of the visible
spectrum.

Brown is defined as:

"Any of a group of colors between red and yellow in hue, of medi

Re: Dial face colouration

[Steve Lelievre]

Hi Kevin,

Yes, I plan to use laser engraving and cutting. There is a local 
community maker workshop that charges $2 per minute of cutting time for 
using their machine with exactly the setup you describe - I choose line 
colours in my PDF depending on whether I will want the areas or line 
rastered, etched or cut, and then I configure the laser to fire at 
different powers for each colour. I've taken to writing my programs in 
Javascript - there's are code libraries for Javascript that allow 
drawing directly into PDF files.


I think I own some of your work - aren't you the KWK who produced Fred 
Sawyer's Universal Nomographic Sundial handed out at a recent NASS 
conference?  The details in that piece are much finer than I have been 
able to achieve on the machine at the workshop. They have a measuring 
device that hangs loosely from the head of the machine. The train us to 
raise or lower the bed until the measuring device only just touches the 
work piece. To my mind that should bring the cone of laser light to a 
perfect point and allow very fine lines - but in practice I've never got 
a line to come out narrower than, I guess, about .5mm even at the lowest 
power setting of the machine. I have the line widths set to .1 mm in my 
PDFs.


I'm starting to suspect that the people who run the facility I use 
aren't very good at calibrating the machine. The guy in charge seems to 
think that it's working a well as can be expected but your work is much, 
much finer. The machine is one of these: http://fslaser.com/Product/Pro3624


I'd welcome your thoughts and advice about this.

Cheers,
Steve







On 2017-02-26 5:39 AM, Kevin Karney wrote:

Dear Steve

I do not know how you are planning to cut and fabricate your plastic 
sheeting. But if you have not looked,  there are many many bi-colour 
double layered UV resistant acrylics used by the sign-writing 
industry. See, for example, 
https://www.engraving-supplies.co.uk/laser-materials/trolase.html. The 
advantage of these materials (or single colour acrylics) is that they 
can be either cut and engraved with great precision and minimal cost 
by laser-cutting. All you need is a good .pdf graphic made to 
appropriate specs for your laser-cutter. Typically, text - which is 
raster-engraved - will be one colour. While vector lines and curves 
will be lines of a certain thickness and of different colours (one 
colour for a cut, others for different depths of engraving).


One of the great advantages of the laser cut approach is that you can 
try endless designs cut/engraved on cardboard - costing virtually 
nothing, before committing to your more expensive final material.


Laser cutting is cheap these days and if you live anywhere near a big 
city, you may find that there is a 'FabLab', where you can go and do 
it yourself - see www.fablabs.io/labs/map 


Having started designing sundials by laser-cutting in Cardiff 
University's FabLab - I am now actually employed there part-time to 
teach others in laser-cutting. So I am happy to elucidate further if 
anyone is interested.


cheers
Kevin


---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Patrick Vyvyan]

When taking light meter readings for photography, it is common to use an
18% grey card in place of the object which will actually be photographed.
This is generally considered to give a reading which will accurately
balance light and dark.

See: https://en.wikipedia.org/wiki/Gray_card

Might be worth examining as an ideal tone for a sundial?




*Patrick Vyvyan*

*Presidente*


*Corporación Cultural de Putaendo*

On 26 February 2017 at 12:08, John Lynes  wrote:

> There is no single optimum reflectance for a flat dial face.  Obviously
> under dim sunlight the optimum reflectance would be 100 per cent,
> i.e.perfect white.
> Under intense sunlight, contrast sensitivity would be optimised for a
> lower value of reflectance.  Thousands of papers have been written on
> contrast sensitivity.  One classical study is "Brightness and contrast in
> illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram,
> Transactions of the Illuminating Engineering Society (London), Vol 6, No 3,
> pp 37-48 (1941).  This indicates that when the sky illuminance on a matt
> dial face is over about 50 lumens per square foot (about 500 lux) the
> optimum reflectance would be about 60 per cent (a light grey, about Munsell
> Value 8).  Below this illuminance (which would correspond to a solar
> altitude close to sunrise or sunset) the optimum reflectance would rise
> quite sharply.
> Note however that the maximum sky illuminance considered by the authors
> was 1000 lumens per square foot (corresponding to a solar altitude of about
> 20 degrees).  Higher illuminances might further reduce the optimum
> reflectance.
> John Lynes
>
> On 26 February 2017 at 02:25, Michael Ossipoff 
> wrote:
>
>> It seems to me that Steve's question has been mostly disregarded rather
>> than answered.
>>
>> Not having experience with translucent dial-faces, I didn't know about
>> their lack of accuracy, and I certainly can't disagree with what two people
>> have said about that.
>>
>> It means that the advantage of a translucent dial, for omnidirectional
>> reading, comes with a disadvantage of less precise accuracy.
>>
>> But of course a high-mounted dial intended for relatively distant reading
>> might not be as concerned with fine accuracy as with omnidirectional
>> viewing. And so translucent dials for all-directions viewing certainly
>> aren't ruled-out.
>>
>> Steve's main question was about the choice of dial-face hue, saturation
>> and brilliance, for easy and safe dial-reading. It seems to me that Steve's
>> question has been mostly disregarded and discounted rather than answered.
>>
>> I lied.
>>
>> I said that I can't speak from experience on that matter.
>>
>> But my experience with a few paper-on-cardboard tablet-dials is
>> sufficient to say this:
>>
>> From my experience, I can say that you definitely don't want a white
>> dial-face.
>>
>> As I said, my first dial had a white dial-face. After that, I switched to
>> brown, which was a big improvement in usability.
>>
>> I suggest brown instead of white.
>>
>> Someone implied that, the more contrast (between light and shadow), the
>> better. Not so, when the dial-face is too white to look at in bright
>> sunlight.
>>
>> As for gray: Gray reflects the visible wavelengths in a relatively equal
>> mix, resulting in no perceived hue. If some hues are (at least relatively)
>> to be avoided, then obviously gray isn't what you want.
>>
>> At each end of the visible spectrum, there is, of course, radiation that
>> isn't visible.
>> Infrared (IR) and ultraviolet (UV).
>>
>>  One possible disadvantage of that is that, when you don't perceive it or
>> its intensity, then of course you could conceivably get a dangerous amount
>> (accutely or cumulatively) without any perception of it.
>>
>> For example, never look at the sun when, due to a haze, or due to the sun
>> being low in the sky, the sun doesn't look bright. You don't have any
>> perception of how ingtense the UV or IR is. It could burn your eye without
>> any feeling of discomfort. (I don't know which of those is more dangerous,
>> but there have been official warnings to never look at the sun when it
>> seems less bright due to haze or low altitude.)
>>
>> Aside from that, there's been evidence that, when people spend a lot of
>> time outdoors, in bright sunny climate, then many years of exposure to the
>> bright blue light can cause some long-term cumulative damage. So maybe blue
>> isn't the most desirable hue.
>>
>> Yellow, beings the complement of blue, looks yellow because it absorbs
>> blue, removes blue from the light that it reflects.
>>
>> Also, yellow isn't particularly close to either end of the visible
>> spectrum.
>>
>> Brown is defined as:
>>
>> "Any of a group of colors between red and yellow in hue, of medium to low
>> brilliance, and of moderate to low saturation."
>>
>> Then, dark brown would be brown with particularly low brilliance--a
>> desirable attribute for a sundial-face. 

Re: Dial face colouration

[John Lynes]

There is no single optimum reflectance for a flat dial face.  Obviously
under dim sunlight the optimum reflectance would be 100 per cent,
i.e.perfect white.
Under intense sunlight, contrast sensitivity would be optimised for a lower
value of reflectance.  Thousands of papers have been written on contrast
sensitivity.  One classical study is "Brightness and contrast in
illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram,
Transactions of the Illuminating Engineering Society (London), Vol 6, No 3,
pp 37-48 (1941).  This indicates that when the sky illuminance on a matt
dial face is over about 50 lumens per square foot (about 500 lux) the
optimum reflectance would be about 60 per cent (a light grey, about Munsell
Value 8).  Below this illuminance (which would correspond to a solar
altitude close to sunrise or sunset) the optimum reflectance would rise
quite sharply.
Note however that the maximum sky illuminance considered by the authors was
1000 lumens per square foot (corresponding to a solar altitude of about 20
degrees).  Higher illuminances might further reduce the optimum reflectance.
John Lynes

On 26 February 2017 at 02:25, Michael Ossipoff 
wrote:

> It seems to me that Steve's question has been mostly disregarded rather
> than answered.
>
> Not having experience with translucent dial-faces, I didn't know about
> their lack of accuracy, and I certainly can't disagree with what two people
> have said about that.
>
> It means that the advantage of a translucent dial, for omnidirectional
> reading, comes with a disadvantage of less precise accuracy.
>
> But of course a high-mounted dial intended for relatively distant reading
> might not be as concerned with fine accuracy as with omnidirectional
> viewing. And so translucent dials for all-directions viewing certainly
> aren't ruled-out.
>
> Steve's main question was about the choice of dial-face hue, saturation
> and brilliance, for easy and safe dial-reading. It seems to me that Steve's
> question has been mostly disregarded and discounted rather than answered.
>
> I lied.
>
> I said that I can't speak from experience on that matter.
>
> But my experience with a few paper-on-cardboard tablet-dials is sufficient
> to say this:
>
> From my experience, I can say that you definitely don't want a white
> dial-face.
>
> As I said, my first dial had a white dial-face. After that, I switched to
> brown, which was a big improvement in usability.
>
> I suggest brown instead of white.
>
> Someone implied that, the more contrast (between light and shadow), the
> better. Not so, when the dial-face is too white to look at in bright
> sunlight.
>
> As for gray: Gray reflects the visible wavelengths in a relatively equal
> mix, resulting in no perceived hue. If some hues are (at least relatively)
> to be avoided, then obviously gray isn't what you want.
>
> At each end of the visible spectrum, there is, of course, radiation that
> isn't visible.
> Infrared (IR) and ultraviolet (UV).
>
>  One possible disadvantage of that is that, when you don't perceive it or
> its intensity, then of course you could conceivably get a dangerous amount
> (accutely or cumulatively) without any perception of it.
>
> For example, never look at the sun when, due to a haze, or due to the sun
> being low in the sky, the sun doesn't look bright. You don't have any
> perception of how ingtense the UV or IR is. It could burn your eye without
> any feeling of discomfort. (I don't know which of those is more dangerous,
> but there have been official warnings to never look at the sun when it
> seems less bright due to haze or low altitude.)
>
> Aside from that, there's been evidence that, when people spend a lot of
> time outdoors, in bright sunny climate, then many years of exposure to the
> bright blue light can cause some long-term cumulative damage. So maybe blue
> isn't the most desirable hue.
>
> Yellow, beings the complement of blue, looks yellow because it absorbs
> blue, removes blue from the light that it reflects.
>
> Also, yellow isn't particularly close to either end of the visible
> spectrum.
>
> Brown is defined as:
>
> "Any of a group of colors between red and yellow in hue, of medium to low
> brilliance, and of moderate to low saturation."
>
> Then, dark brown would be brown with particularly low brilliance--a
> desirable attribute for a sundial-face. Might that be the best color for a
> dial-face?
>
> Tan is defined as:
>
> "Light yellowish brown."
>
> ...suggesting more brilliance than brown (but surely a lot less than
> white), and enough saturation to be perceived as yellow, which seems a good
> thing.
>
> Brown, especially dark brown, or maybe tan, sound like acceptable colors
> for a dial-face.
>
> By the way, beige is defined as:
>
> "A variable color averaging light grayish yellowish brown."
>
> Sounds like tan, but with distinct grayness, lower saturation, making it
> probably less desirable.
>
> In my previous post I said that I 

Re: Dial face colouration

[Kevin Karney]

Dear Steve

I do not know how you are planning to cut and fabricate your plastic sheeting. 
But if you have not looked,  there are many many bi-colour double layered UV 
resistant acrylics used by the sign-writing industry. See, for example, 
https://www.engraving-supplies.co.uk/laser-materials/trolase.html 
. The 
advantage of these materials (or single colour acrylics) is that they can be 
either cut and engraved with great precision and minimal cost by laser-cutting. 
All you need is a good .pdf graphic made to appropriate specs for your 
laser-cutter. Typically, text - which is raster-engraved - will be one colour. 
While vector lines and curves will be lines of a certain thickness and of 
different colours (one colour for a cut, others for different depths of 
engraving).

One of the great advantages of the laser cut approach is that you can try 
endless designs cut/engraved on cardboard - costing virtually nothing, before 
committing to your more expensive final material.

Laser cutting is cheap these days and if you live anywhere near a big city, you 
may find that there is a 'FabLab', where you can go and do it yourself - see 
www.fablabs.io/labs/map 

Having started designing sundials by laser-cutting in Cardiff University's 
FabLab - I am now actually employed there part-time to teach others in 
laser-cutting. So I am happy to elucidate further if anyone is interested.

cheers
Kevin

> On 24 Feb 2017, at 18:04, Steve Lelievre  
> wrote:
> 
> Fellow sundiallers,
> 
> I’m planning to make my next sundial from outdoor grade UV resistant plastic 
> sheeting. These come in a range of colours and I want to choose one that 
> works well for a sundial. Assuming I get the material grit-blasted or somehow 
> treated so that it not shiny, and leaving aesthetic considerations aside, 
> what light-related attributes should I be looking for?
> 
> As anyone who has played with paper sundials knows, a white surface is hard 
> to look at in full sun, even if non-shiny; black would not show any shadow. I 
> need something in between: light enough to catch a shadow, but dark enough to 
> avoid glare in full sun. I assume that latitude has a bearing on this, as the 
> midday sun illuminates more strongly as we approach the equator. In my case, 
> the design latitude is around 45 N. My dial will be about 25cm in diameter.
> 
> Are there any conventions or empirical guidelines, or even practical 
> experience, to help me choose?
> 
> Which properties matter? I quick read of Wikipedia suggests colours seem to 
> involve hue, saturation or luminosity (or parallel concepts in other 
> classifications).
> 
> Cheers,
> Steve
> 
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
> 

---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Thibaud Taudin Chabot]

My experience is use a mat finish sand color. It 
also matches with nearly every colorscheme.


At 03:25 26-2-2017, Michael Ossipoff wrote:
It seems to me that Steve's question has been 
mostly disregarded rather than answered.


Not having experience with translucent 
dial-faces, I didn't know about their lack of 
accuracy, and I certainly can't disagree with 
what two people have said about that.


It means that the advantage of a translucent 
dial, for omnidirectional reading, comes with a 
disadvantage of less precise accuracy.


But of course a high-mounted dial intended for 
relatively distant reading might not be as 
concerned with fine accuracy as with 
omnidirectional viewing. And so translucent 
dials for all-directions viewing certainly aren't ruled-out.


Steve's main question was about the choice of 
dial-face hue, saturation and brilliance, for 
easy and safe dial-reading. It seems to me that 
Steve's question has been mostly disregarded and 
discounted rather than answered.


I lied.

I said that I can't speak from experience on that matter.

But my experience with a few paper-on-cardboard 
tablet-dials is sufficient to say this:


From my experience, I can say that you 
definitely don't want a white dial-face.


As I said, my first dial had a white dial-face. 
After that, I switched to brown, which was a big improvement in usability.


I suggest brown instead of white.

Someone implied that, the more contrast (between 
light and shadow), the better. Not so, when the 
dial-face is too white to look at in bright sunlight.


As for gray: Gray reflects the visible 
wavelengths in a relatively equal mix, resulting 
in no perceived hue. If some hues are (at least 
relatively) to be avoided, then obviously gray isn't what you want.


At each end of the visible spectrum, there is, 
of course, radiation that isn't visible.

Infrared (IR) and ultraviolet (UV).

 One possible disadvantage of that is that, 
when you don't perceive it or its intensity, 
then of course you could conceivably get a 
dangerous amount (accutely or cumulatively) without any perception of it.


For example, never look at the sun when, due to 
a haze, or due to the sun being low in the sky, 
the sun doesn't look bright. You don't have any 
perception of how ingtense the UV or IR is. It 
could burn your eye without any feeling of 
discomfort. (I don't know which of those is more 
dangerous, but there have been official warnings 
to never look at the sun when it seems less 
bright due to haze or low altitude.)


Aside from that, there's been evidence that, 
when people spend a lot of time outdoors, in 
bright sunny climate, then many years of 
exposure to the bright blue light can cause some 
long-term cumulative damage. So maybe blue isn't the most desirable hue.


Yellow, beings the complement of blue, looks 
yellow because it absorbs blue, removes blue from the light that it reflects.


Also, yellow isn't particularly close to either end of the visible spectrum.

Brown is defined as:

"Any of a group of colors between red and yellow 
in hue, of medium to low brilliance, and of moderate to low saturation."


Then, dark brown would be brown with 
particularly low brilliance--a desirable 
attribute for a sundial-face. Might that be the best color for a dial-face?


Tan is defined as:

"Light yellowish brown."

...suggesting more brilliance than brown (but 
surely a lot less than white), and enough 
saturation to be perceived as yellow, which seems a good thing.


Brown, especially dark brown, or maybe tan, 
sound like acceptable colors for a dial-face.


By the way, beige is defined as:

"A variable color averaging light grayish yellowish brown."Â

Sounds like tan, but with distinct grayness, 
lower saturation, making it probably less desirable.


In my previous post I said that I bought brown 
construction-paper, but didn't use it, and, 
instead, just marked the hour-lines on the 
corrugated cardboard instead of using paper. 
Actually, I probably did use the brown 
construction-paper. It looks better of course, 
and it allowed me to conveniently use a 
carbon-paper template that I'd prepared for drawing the hour-lines.


Maybe the plain cardboard dial-face would have 
easier construction in one way, and less easy 
construction in another way. Maybe I tried one 
all-cardboard dial. It was a long time ago.


Michael Ossipoff





Â









On Fri, Feb 24, 2017 at 1:04 PM, Steve Lelievre 
<steve.lelievre.can...@gmail.com> 
wrote:

Fellow sundiallers,

I’m planning to make my next sundial from 
outdoor grade UV resistant plastic sheeting. 
These come in a range of colours and I want to 
choose one that works well for a sundial. 
Assuming I get the material grit-blasted or 
somehow treated so that it not shiny, and 
leaving aesthetic considerations aside, what 
light-related attributes should I be looking for?


As anyone who has played with paper sundials 
knows, a white surface is hard 

Re: Dial face colouration

[Steve Lelievre]

Hi again,

Thank you to everyone who has replied to my inquiry so far.

The comments have been useful and interesting but Michael is right, what 
I am mostly asking about is the limit for how bright my dial face can 
be. Here's what I've discovered since I posted the question - it has 
been cloudy here nearly all day so I got some time with my friend Google.


I learned that the everyday term glare is is also used in a technical 
sense with the same meaning - a source of light (either an area or a 
point) that is so bright it is unpleasant to look at. Apparently it 
comes in two varieties: discomfort glare (unpleasant but not dangerous) 
and disability glare (injury causing, such as the glare experienced if 
one were to look directly at the midday sun or a powerful laser). It's 
fairly easy to find material on the internet relating to disability 
glare, but it doesn't seem relevant to my question. It is also fairly 
easy to find material relating to discomfort glare. Unfortunately what I 
found is generally related to the correct lighting levels for indoor 
workplaces, and the consequences for workplace health and safety. I 
haven't found anything about glare caused by a bright outdoors surface.


The stuff on indoor workplace glare suggests that glare becomes a 
problem when there is a very bright area in one part of our visual 
field, with much dimmer areas around it - for example a window on a 
bright sky bringing light into an inadequately illuminated office. The 
solution is to add more lighting to the office so that the internal 
surfaces are as bright as the window. So, I have found lots  of stuff on 
minimum levels of background luminance (or brightness), but not much on 
maximum levels for objects being observed.


I did a bit of experimentation in the few cloudless minutes that we had 
in Vancouver today. I played around with paint sample cards for various 
reds, blues, greens, browns and greys, ranging from very dark to very 
pale, almost white.


Michael was right: much to my surprise, even a near-black matte surface 
will catch a shadow! On the other hand, it needs direct sunlight. The 
shadow on my darkest cards becomes very difficult to make out if the sun 
is covered by thin cloud or haze - a situation when the pale cards will 
still easily show a shadow (albeit slightly blurred).


My brief testing so far suggests that hue (what we ordinarily call 
colour) and saturation (colour versus grayness) are unimportant to how 
well a shadow forms, whereas luminance (the amount of incoming light 
that is radiated back towards the observer) and specularity (matte 
versus mirrored) seem more important. The issue is that luminous or 
specular surfaces cause glare.


In practice I judged that for each of my sets of cards, only the darkest 
ones would not work as a dial face in practice. I also judged that the 
lightest ones would be too bright. Each colour set is 8 cards, so that 
leaves 3 or 4 cards in the middle that all looked as if they work work 
out fine.


I was doing my testing at about 9:30 in the morning in the late winter, 
so the sun was relatively low in the sky. Perhaps those middle cards 
would be too bright in the midday summer sun - I got no feeling for 
that. As well, the cards are only 4 cm square. My dial would be a 
hundred times the area. I don't know if that would affect it.



That's all for now. I'll keep you posted as I discover more.

Steve





















On 2017-02-25 6:25 PM, Michael Ossipoff wrote:
It seems to me that Steve's question has been mostly disregarded 
rather than answered.


Not having experience with translucent dial-faces, I didn't know about 
their lack of accuracy, and I certainly can't disagree with what two 
people have said about that.


It means that the advantage of a translucent dial, for omnidirectional 
reading, comes with a disadvantage of less precise accuracy.


But of course a high-mounted dial intended for relatively distant 
reading might not be as concerned with fine accuracy as with 
omnidirectional viewing. And so translucent dials for all-directions 
viewing certainly aren't ruled-out.


Steve's main question was about the choice of dial-face hue, 
saturation and brilliance, for easy and safe dial-reading. It seems to 
me that Steve's question has been mostly disregarded and discounted 
rather than answered.


I lied.

I said that I can't speak from experience on that matter.

But my experience with a few paper-on-cardboard tablet-dials is 
sufficient to say this:


From my experience, I can say that you definitely don't want a white 
dial-face.


As I said, my first dial had a white dial-face. After that, I switched 
to brown, which was a big improvement in usability.


I suggest brown instead of white.

Someone implied that, the more contrast (between light and shadow), 
the better. Not so, when the dial-face is too white to look at in 
bright sunlight.


As for gray: Gray reflects the visible wavelengths in a relatively 
equal 

Re: Dial face colouration

[Michael Ossipoff]

It seems to me that Steve's question has been mostly disregarded rather
than answered.

Not having experience with translucent dial-faces, I didn't know about
their lack of accuracy, and I certainly can't disagree with what two people
have said about that.

It means that the advantage of a translucent dial, for omnidirectional
reading, comes with a disadvantage of less precise accuracy.

But of course a high-mounted dial intended for relatively distant reading
might not be as concerned with fine accuracy as with omnidirectional
viewing. And so translucent dials for all-directions viewing certainly
aren't ruled-out.

Steve's main question was about the choice of dial-face hue, saturation and
brilliance, for easy and safe dial-reading. It seems to me that Steve's
question has been mostly disregarded and discounted rather than answered.

I lied.

I said that I can't speak from experience on that matter.

But my experience with a few paper-on-cardboard tablet-dials is sufficient
to say this:

>From my experience, I can say that you definitely don't want a white
dial-face.

As I said, my first dial had a white dial-face. After that, I switched to
brown, which was a big improvement in usability.

I suggest brown instead of white.

Someone implied that, the more contrast (between light and shadow), the
better. Not so, when the dial-face is too white to look at in bright
sunlight.

As for gray: Gray reflects the visible wavelengths in a relatively equal
mix, resulting in no perceived hue. If some hues are (at least relatively)
to be avoided, then obviously gray isn't what you want.

At each end of the visible spectrum, there is, of course, radiation that
isn't visible.
Infrared (IR) and ultraviolet (UV).

 One possible disadvantage of that is that, when you don't perceive it or
its intensity, then of course you could conceivably get a dangerous amount
(accutely or cumulatively) without any perception of it.

For example, never look at the sun when, due to a haze, or due to the sun
being low in the sky, the sun doesn't look bright. You don't have any
perception of how ingtense the UV or IR is. It could burn your eye without
any feeling of discomfort. (I don't know which of those is more dangerous,
but there have been official warnings to never look at the sun when it
seems less bright due to haze or low altitude.)

Aside from that, there's been evidence that, when people spend a lot of
time outdoors, in bright sunny climate, then many years of exposure to the
bright blue light can cause some long-term cumulative damage. So maybe blue
isn't the most desirable hue.

Yellow, beings the complement of blue, looks yellow because it absorbs
blue, removes blue from the light that it reflects.

Also, yellow isn't particularly close to either end of the visible spectrum.

Brown is defined as:

"Any of a group of colors between red and yellow in hue, of medium to low
brilliance, and of moderate to low saturation."

Then, dark brown would be brown with particularly low brilliance--a
desirable attribute for a sundial-face. Might that be the best color for a
dial-face?

Tan is defined as:

"Light yellowish brown."

...suggesting more brilliance than brown (but surely a lot less than
white), and enough saturation to be perceived as yellow, which seems a good
thing.

Brown, especially dark brown, or maybe tan, sound like acceptable colors
for a dial-face.

By the way, beige is defined as:

"A variable color averaging light grayish yellowish brown."

Sounds like tan, but with distinct grayness, lower saturation, making it
probably less desirable.

In my previous post I said that I bought brown construction-paper, but
didn't use it, and, instead, just marked the hour-lines on the corrugated
cardboard instead of using paper. Actually, I probably did use the brown
construction-paper. It looks better of course, and it allowed me to
conveniently use a carbon-paper template that I'd prepared for drawing the
hour-lines.

Maybe the plain cardboard dial-face would have easier construction in one
way, and less easy construction in another way. Maybe I tried one
all-cardboard dial. It was a long time ago.

Michael Ossipoff















On Fri, Feb 24, 2017 at 1:04 PM, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> Fellow sundiallers,
>
> I’m planning to make my next sundial from outdoor grade UV resistant
> plastic sheeting. These come in a range of colours and I want to choose one
> that works well for a sundial. Assuming I get the material grit-blasted or
> somehow treated so that it not shiny, and leaving aesthetic considerations
> aside, what light-related attributes should I be looking for?
>
> As anyone who has played with paper sundials knows, a white surface is
> hard to look at in full sun, even if non-shiny; black would not show any
> shadow. I need something in between: light enough to catch a shadow, but
> dark enough to avoid glare in full sun. I assume that latitude has a
> bearing on this, as the midday sun 

RE: Dial face colouration

[Jackie Jones]

Hi Steve,

I agree with Roger; opaque is far better than translucent.  Also, as he says, 
it is the shade or tone that really matters; try cards in different shades to 
see what works best in your light.  I would suggest that colour is important 
from a design perspective; what other colours does it have to blend with?  Such 
as the colour of your house, for example.  But check with the plastic sheeting 
manufacturer, UV resistant means that the plastic will not decay; but will the 
colour last?  When I painted the dial on the front of my house I checked the 
paint manufactures details as to the permanency of the colours and used the 
ones with a longer colour life.

With best wishes,
Jackie

Jackie Jones
50° 50’ 09” N0° 07’ 40” W

  

-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Roger Bailey
Sent: Saturday, February 25, 2017 3:38 AM
To: sundial@uni-koeln.de; Steve Lelievre
Subject: Re: Dial face colouration

Hello Steve,

Consider translucence, the diffusion of light on the substrate. This 
semi-transparency diffuses the contrast between light and shadow. Plastic, 
glass even rock can be translucent  and compromise the shadow on a surface. 
I have noticed this problem with high quality Carrara marble, smoky glass, 
porcelain and plastic slabs. An opaque, non-reflective surface like grey 
oolitic limestone is best.

Colour is just a distraction. The contrasts of shades of grey from bright 
sunlight to dark shadows are our medium.

Roger Bailey
Walking Shadow Designs

--
From: "Steve Lelievre" <steve.lelievre.can...@gmail.com>
Sent: Friday, February 24, 2017 10:04 AM
To: <sundial@uni-koeln.de>
Subject: Dial face colouration

> Fellow sundiallers,
>
> I’m planning to make my next sundial from outdoor grade UV resistant 
> plastic sheeting. These come in a range of colours and I want to 
> choose one that works well for a sundial. Assuming I get the material 
> grit-blasted or somehow treated so that it not shiny, and leaving 
> aesthetic considerations aside, what light-related attributes should I 
> be looking for?
>
> As anyone who has played with paper sundials knows, a white surface is 
> hard to look at in full sun, even if non-shiny; black would not show 
> any shadow. I need something in between: light enough to catch a 
> shadow, but dark enough to avoid glare in full sun. I assume that 
> latitude has a bearing on this, as the midday sun illuminates more 
> strongly as we approach the equator. In my case, the design latitude 
> is around 45 N. My dial will be about 25cm in diameter.
>
> Are there any conventions or empirical guidelines, or even practical 
> experience, to help me choose?
>
> Which properties matter? I quick read of Wikipedia suggests colours 
> seem to involve hue, saturation or luminosity (or parallel concepts in 
> other classifications).
>
> Cheers,
> Steve
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
>
> -
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2016.0.7998 / Virus Database: 4756/14015 - Release Date: 
> 02/24/17
> 
---
https://lists.uni-koeln.de/mailman/listinfo/sundial


---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Dial face colouration

[Michael Ossipoff]

On Fri, Feb 24, 2017 at 1:04 PM, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> Fellow sundiallers,
>
> I’m planning to make my next sundial from outdoor grade UV resistant
> plastic sheeting. These come in a range of colours and I want to choose one
> that works well for a sundial. Assuming I get the material grit-blasted or
> somehow treated so that it not shiny, and leaving aesthetic considerations
> aside, what light-related attributes should I be looking for?
>
> As anyone who has played with paper sundials knows, a white surface is
> hard to look at in full sun, even if non-shiny; black would not show any
> shadow.


Well, one would have to try it to be sure. Maybe black would work, because
nothing is *completely* absorbent. So why not start with the least
reflective color, black.  ...and then try something else if the shadow
isn't visible.

I've never made a durable waterproof, windproof fixed-mounted outdoor
sundial, and so I'm just guessing, not speaking from experience. I made a
few pocket tablet-dials. My first one was typewriter-paper (computer-paper
now) on corrugated cardboard. Too bright to look at, of course. So, for the
rest of them, I got some brown construction-paper, but, instead of using
it, I just drew the hour-lines on the brown corrugated cardboard, instead
of pasting paper to it.

I, too, would be interested in hearing about the conventions, empirical
guidelines, or practical experience. I probably would have asked that
question sooner or later.

Yes, I've heard the color-attributes referred to as hue, saturation, and
brilliance. I'm sure that luminosity means the same as brilliance. Maybe
"brilliance" is better, because it doesn't carry any implication of the
object being a *source*.

I'm sure that brilliance is important, and probably is the most important
attribute.

It seems to me that I once read that brown is a low-brilliance
orange-yellow mix.

Hue could matter if some hues, wavelengths, are more damaging, irritating
or annoying than others. Of course the lower the saturation, the more
grayish, the more nearly the reflected light is an equal mixture of the
visible-light wavelengths. So, if some hues are more desirable than others,
then low saturation, grayish-ness, wouldn't serve any purpose.

We hear that, among the visible colors, blue is less desirable to look at a
lot of. Maybe partly because of its own effect, and partly because it's
nearer to the uv end of the spectrum. Yellow is the complement of blue. And
red and orange are at the opposite end of the visible spectrum from blue.

So, low brilliance, probably preferably high saturation (less grayish),
yellow orange or red?

I think that means brown, but it was a long time ago when I read about it.

If trying brown, might as well start with dark brown.

If brown isn't available, then maybe dark tan. If that isn't available,
then maybe dark red or dark orange (or maybe "dark orange" is the same as
brown or tan)?

I don't claim to have the answer to that question--just a few guesses. No
doubt someone will be able to genuinely answer the question.

Will this be a horizontal sundial, or a higher-mounted sundial intended to
be visible from farther away, for visibility to neighbors or passers-by who
aren't near enough to look down at it?

The translucency of the materials you speak of could be helpful if it's to
be viewed at a distance, because a translucent flat dial can be read from
all directions; and, if it has a gnomon on each side, then it has a shadow
regardless of which side of it the sun is on.

An equatorial flat dial has the advantage that its construction-principle
is the most immediately-obvious to all neighbors and passers-by. Unless
translucent, of course it's only readable from one side during either
particular half of the year.

Next easiest to explain the construction of, is the horizontal-dial. Has
shadow all day, all year, and readable from all directions if you're
standing near enough to it. But maybe not everyone is that near to it.

And, after that, the easiest to explain the construction of are the the
flat dials whose dial-plate-normal (perpendicular line) is in the plane of
the meridian: That's a south-facing vertical dial, or a south-facing
reclining dial. (But if the necessary visibility-direction called for it, I
suppose it could be a fairly-nearly-horizontal north-facing reclining dial
too, though it of course wouldn't have as much coverage of hours and
seasons.)

If you want the construction to be easily-explained to people, then you
wouldn't use a declining, or reclining-declining dial. But of course
sometimes visibility-direction requirements could make one necessary,
especially with non-translucent, non-transparent dial-face material.

All this from someone who has never built a durable, waterproof, windproof,
fixed-mounted outdoor sundial :^)

There are a lot of questions that I'd ask about that. I'll save those for
another post, sometime.

Well, one question now:

Were