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
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
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
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
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
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
eln.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
wil
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
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
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
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,
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
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
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
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 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.
16 matches
Mail list logo
