[VAC] Re: LED Ambience and lighting.

[Dr. Gerald N. Johnson, electrical engineer]

There was a large assortment of all kinds of bases of LED lamp
assemblies at www.ledtronics.com. I didn't find prices. There are
bayonet based lamps in Allied Electronics, but no specifications as to
performance, for about $21.35 each.

There is a LOT of specmanship in the LED industry. Most of the time it
appears the intensity is based on the peak intensity of a focused beam,
while the output of an incandescent lamp is the average over a whole
sphere. And makers of LEDs with output of only 10 or 20 millicandela
claim super brightness. 25 years ago 1 millicandela was on the bright
side for the average LED so 10, 20, or 250 comparatively is super
bright. To look at. To use as illumination for working and reading, its
almost enough to know its turned on, but not enough for practical work.
Similarly some makers call 1000 millicandela ultra bright, but that's
one candela or one candle power, and the apparent state of the art is at
least 7 candela for white, 35 candela for orange. Far too many catalog
pages I have of LEDs and LED assemblies use only the adjectives, not
real numbers for peak intensity and beam spread. The 1141 incandescent
lamps in my Caravel each are rated to put out 21 mean spherical candela,
e.g. average 21 candle power in all directions. The fixtures using them
get only a fraction of that out to useful places and then poorly because
of the central location of the fixture compared to tasks.

At the moment (and still from thinking under the covers overnight last
night) I'm thinking that if a task area the size of the stove top can be
lit with one or two LEDs (or maybe a few) right above on the bottom of
the cabinet, then a couple more can do the sink and a couple more the
counter top next to the sink. Very much task lighting. That would suit
me. I have an industrial light meter so will be able to make
measurements with a bit of accuracy, to be more effective than eyeball
impressions. I think that by dedicating a LED or two to a task area the
size of the stove or sink, that the process has the best chance of
working. The light will be put where its needed, not bounced around the
trailer for ambience. Light on the task is far more useful that light on
the back of my head (where I can't see it and it annoys visitors from
the glare off the bare skin). It won't be as simple as plugging in
factory made assemblies, but when those factory assemblies light up a
couple square foot of wall, not the floor or counter top, I question
their benefit. One group of them mounts several LEDs headed out the top
of the lamp assembly. Ledtronics makes bayonet base lamps that shine to
the sides, but in two directions at once. So if turned to put one side
on the counter top or dinette table, the other is most wasted trying to
reflect off a dull metal surface. Even with a mirror mounted for
reflecting most of the light would end up back in the LEDs not on the
table top. Ledtronics also makes more or less spherical arrays of LEDs
in larger envelopes. Still in every fixture I have in this house, half
the LEDs wouldn't be putting light in a useful direction. There may be a
need to acquire a metalized mylar "blanket" to cut up for reflectors in
fixtures when LEDs are plugged in.

The typical Ledtronics assembly tends to take 1 to 2 watts from its
power source which can be 12/14 volts, 24 volts, and other voltages up
through 120 volts and 240 volts.

I saw a circuit this evening from Maxim of a switching regulator set to
regulate the current through LEDs, running at least half a dozen in
series from a 3 volt supply. It was also a voltage step up circuit.
Might run several more LEDs from a 12 volt supply. There does appear to
be far more circuit solutions than problem. And what is right this week
may be not as great next week. Similarly what is the best LED this week
will be outdated by announcements of better products next week, though
it may take a year for those better products to arrive in the flesh, and
by then further better products will have been announced.

Gerald J.



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