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Using red + green + blue Christmas LEDs to form white light

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Weltanscha

Jan 1, 1970
0
For a few years now I've been lighting our bedroom mainly with white
Christmas lights strung across the ceiling. They've gotten pretty dim
and burned out by now, and need replacing. But they seem to heat the
room up quite a bit in summer, plus I'm getting somewhat bored with
them, so I'd like to try something a little different.

Red, green, and blue light is supposed to stimulate the red, green, and
blue cones in the eye to give the sensation of white in combination, so
I thought it might be nice to use strings of those colors, rather than
white strings. I think it'd be interesting to see colored lights when
you look up at the ceiling, but essentially white down below, where the
light is better mixed. But it seems like a bad idea to use
conventional incandescent lighting for that, since each bulb produces a
full spectrum of light which is then selectively filtered by the bulb
color coating, resulting in dimmer light, warmer room, more
electricity, sadder polar bears, etc.

It's my understanding, however, that LED Christmas lights are very
efficient, more so since the colored ones only give out narrow-spectrum
light. So I think I'd like to use them. But I have no idea about the
relative intensities of the R, G, and B that LEDs give of, and thus how
well they'll "fool" the cones. (And I see people complaining that
"white" LEDs often seem more blue than white.) Yeah, I know, I could
just buy three strings and check it out for myself, but before doing
that I thought I'd ask whether anyone else has tried this before, or
has any ideas on the subject. In particular, is there any way to get
output specs for the strings, and use that somehow?

Also, does anyone know how many LED lights one can safely attach to an
outlet?

And on a semi-related concept, after reading about how LED computer
monitors work, the question occurs to me: would it be better for screen
longevity and power consumption to use a desktop background that's all
white, or all black? Or doesn't it make any difference?
 
Weltanscha said:
For a few years now I've been lighting our bedroom mainly with white
Christmas lights strung across the ceiling. They've gotten pretty dim
and burned out by now, and need replacing. But they seem to heat the
room up quite a bit in summer, plus I'm getting somewhat bored with
them, so I'd like to try something a little different.


Have you considered using a compact fluorescent bulb?

;-)
 
R

Rich Grise

Jan 1, 1970
0
Also, does anyone know how many LED lights one can safely attach to an
outlet?

If by "safely", you mean "won't burn the house down", then with a
standard (US) 120V, 15A outlet, you could burn 1,800 watts of power.

Say your LEDs have an average Vf of 3V and an average current of
20mA - that's 3 * .02 = .06 watts per LED, so 30,000, if you want
to sit there and solder them all up. ;-)

Nah, cancel that - you're going to lose anywhere from 10-50% of
your power in the current limiting resistors, albeit series strings
would help there.

Have Fun!
Rich
 
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Weltanscha

Jan 1, 1970
0
Have you considered using a compact fluorescent bulb?

;-)

I was keeping the story short, but I use both the Christmas lights and
track lights with the compact fluorescents, both on one switch. The
resulting atmosphere is homey/romantic meets nasty interrogation scene.
Don't like it that way, meant to change it to two switches, never got
around to it. Mostly I point the track lights so they're as
unobtrusive as possible. I'll change it, someday. On the other hand,
if I wait a little longer I'll be creeping up on a decade of
procrastination, which is surely something to be proud of.
 
R

Rich Grise

Jan 1, 1970
0
.
as possible. I'll change it, someday. On the other hand, if I wait a
little longer I'll be creeping up on a decade of procrastination, which is
surely something to be proud of.

A decade??? ONE decade???????

***AMATEUR!!!!!*** ;-)

I've been meaning to join the Procrastinators' Club for going on 40
years now! ;-)

Cheers!
Rich
 
I

Impmon

Jan 1, 1970
0
Also, does anyone know how many LED lights one can safely attach to an
outlet?

A 35 LED set wired in series with a current limiting resistor was
labeled as taking about 4.8 watts per set max so 35 LED off 120v would
be about 0.04A max which is a bit higher than typical LED forward
current. A 70 LED string would probably be the same but without the
current limiting resistor since the total max voltage would be 140v
DC.

So theorically you could have more than 300 LED light strings off a
single typical 15A household outlet and not even get close to warm.
Time to stock up on assorted multi-outlet adapters.
And on a semi-related concept, after reading about how LED computer
monitors work, the question occurs to me: would it be better for screen
longevity and power consumption to use a desktop background that's all
white, or all black? Or doesn't it make any difference?

Power consuption wise: all black = all LED off. As for the advertised
life cycle, the companies tended to be on the conservative side. When
I bought an LCD monitor, it was claimed to about 10,000 hours for the
backlight. My monitor has been on for almost 3 years 24/7 now and that
is over 30,000 hours.

LED can last a lot longer than CCFL so you could probably get 7-8
years of 24/7 without a problem. By then, somehting better would come
around to replace the LED monitor.
 
I

Impmon

Jan 1, 1970
0
I've been meaning to join the Procrastinators' Club for going on 40
years now! ;-)

You have a club? No one bothered to form any locally because no one
could be bothered to show up and organize a club charter.
 
P

Puckdropper

Jan 1, 1970
0
You have a club? No one bothered to form any locally because no one
could be bothered to show up and organize a club charter.

Was it formed Jan 2? You know, the day you try to keep your resolutions.

Puckdropper
 
D

Don Klipstein

Jan 1, 1970
0
But I have no idea about the
relative intensities of the R, G, and B that LEDs give of, and thus how
well they'll "fool" the cones.

I have a bit of past experience indicating that to get white light, you
need:

1) Really good color mixing

2) Number of green LEDs roughly twice the number of blue ones, and number
of red LEDs roughly 3 times the number of blue ones. This will vary with
efficiency of your particular LEDs.

If you want a warmer shade of white, use fewer blue ones, replacing them
with red more than green.

So far in my experience, equal number of red, green and blue LEDs gives
a roughly sky blue color.

- Don Klipstein ([email protected])
 
M

Michael A. Terrell

Jan 1, 1970
0
Puckdropper said:
Was it formed Jan 2? You know, the day you try to keep your resolutions.


I have only made one "New Year's Resolution" in my life, and that was
that I'd never make another. I've kept it for over 40 years.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
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Rich Grise

Jan 1, 1970
0
I have only made one "New Year's Resolution" in my life, and that was
that I'd never make another. I've kept it for over 40 years.

Hey! Stop stealing my lines! ;-)

Cheers!
Rich
 
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Weltanscha

Jan 1, 1970
0
Impmon said:
Power consuption wise: all black = all LED off.

Oops! I meant to write "LCD," but was stuck in the "LED" groove.

The reason I'm asking is that, according to what I read, in LCD
displays there's a white backlight that's always on, passing white
light through a vertically-polarizing filter, then through the LC, then
through a horizontally-polarizing filter in front. If there's a
voltage applied across the LC, the vertically-polarized light passes
through it with polarization unchanged, thus it's blocked by the filter
in front. So it seems to me at the very least, there's no power cost
to having a white-wallpapered screen versus a black one. So I'm
wondering about burn-in (or rather the equivalent).

- Tom
 
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Weltanscha

Jan 1, 1970
0
Don said:
I have a bit of past experience indicating that to get white light, you
need:

1) Really good color mixing

2) Number of green LEDs roughly twice the number of blue ones, and number
of red LEDs roughly 3 times the number of blue ones. This will vary with
efficiency of your particular LEDs.

If you want a warmer shade of white, use fewer blue ones, replacing them
with red more than green.

So far in my experience, equal number of red, green and blue LEDs gives
a roughly sky blue color.

Hey, thanks, Don, that's the kind of info I'm looking for.

Just for the hell of it, I set up the background on my three-monitor
computer display to show a grid of R, G, and B squares, just to see how
tiny I had to make the squares to get a good blend. Not too small at
all, as it turns out. On the other hand, maybe it wasn't such a good
test, because it wasn't very bright at all, and not LED of course.

BTW, Richard Dawkins asks what I thoght was an interesting question in
one of his books: Pure green light stimulates all three kinds of color
receptors, to a greater or lesser degree. What do you suppose you'd
see if you could somehow stimulate the green, and *only* the green,
receptors?

- Tom
 
Weltanscha said:
Hey, thanks, Don, that's the kind of info I'm looking for.

Just for the hell of it, I set up the background on my three-monitor
computer display to show a grid of R, G, and B squares, just to see how
tiny I had to make the squares to get a good blend. Not too small at
all, as it turns out. On the other hand, maybe it wasn't such a good
test, because it wasn't very bright at all, and not LED of course.

BTW, Richard Dawkins asks what I thoght was an interesting question in
one of his books: Pure green light stimulates all three kinds of color
receptors, to a greater or lesser degree. What do you suppose you'd
see if you could somehow stimulate the green, and *only* the green,
receptors?

- Tom



Dunno, but you might like reading this:

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html
 
B

Bob Myers

Jan 1, 1970
0
Weltanscha said:
Oops! I meant to write "LCD," but was stuck in the "LED" groove.

In an LCD monitor, the bulk of the power is in the backlight; the
state of the LCD itself (pixels on or pixels off) makes little difference.
Plus, there are both flavors of pixel technology - "white" when on,
and "black" when on - in common use, so it's hard to make a general
statement about whether all-white screens or all-black will be the
most power hungry.

For LEDs, of course - organic LEDs, or OLEDs, being the only
LED technology likely to make it to the desktop - you're right:
"white" means "everything on," and is the highest power
consumption.

Burn-in is not (today, at least) a significant concern with LCDs.
There has been in the past some problems with what was called
"image sticking" in various LCD types, but modern drive methods
have in most cases eliminated this (or you may still see some sticking,
but it is not caused by permanent damage to the panel - i.e., it
can be reversed by applying the proper drive signals).

Bob M.
 
D

Don Klipstein

Jan 1, 1970
0
Don Klipstein wrote: (I edit for space)

Hey, thanks, Don, that's the kind of info I'm looking for.

Just for the hell of it, I set up the background on my three-monitor
computer display to show a grid of R, G, and B squares, just to see how
tiny I had to make the squares to get a good blend. Not too small at
all, as it turns out. On the other hand, maybe it wasn't such a good
test, because it wasn't very bright at all, and not LED of course.

The problems I had with LED color mixing include the different color
ones having different light distribution patterns, causing a smeary
"pattern" of varying color. Some spots are a little more red, some less
red, some more green, some less green, some more blue, and some less blue.
Unless you solve that, the illuminated area could look messy.
BTW, Richard Dawkins asks what I thoght was an interesting question in
one of his books: Pure green light stimulates all three kinds of color
receptors, to a greater or lesser degree. What do you suppose you'd
see if you could somehow stimulate the green, and *only* the green,
receptors?

A deeper shade of green. Try being in a magenta-illuminated room or
cover your eyes with magenta glasses or a diffuser illuminated with
magenta light to get your red and blue receptors less sensitive and your
green ones more sensitive, then see what a pure green light looks like.
(Such as a spot on a wall illuminated by a 532 nm laser or a green LED
behind a few layers of green "plexiglas").

- Don Klipstein ([email protected])
 
D

Don Klipstein

Jan 1, 1970
0
BTW, Richard Dawkins asks what I thoght was an interesting question in
one of his books: Pure green light stimulates all three kinds of color
receptors, to a greater or lesser degree. What do you suppose you'd
see if you could somehow stimulate the green, and *only* the green,
receptors?

Dunno, but you might like reading this:

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html[/QUOTE]

The curves in the page linked from there look "off" to me. For one
thing, the blue one (often called "S" for shortest wavelength one) is
shown at almost half its peak at 400 nm - depending on whose determination
(see below), it's more like 4-10% of peak at 400 nm.
Also, they all look a little broader and more symmetric than they should
be.

For what I consider better "cone fundamental" functions, go to:

http://cvrl.ioo.ucl.ac.uk/cones.htm

Sorry, no curves - these are text files.

There are several versions and determinations.

- Don Klipstein ([email protected])
 
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