low-cost LED-based "one sun" light source

Does anyone here know about making a low-cost LED-based "one sun" light source? Commercial sources are large and expensive. Yes, they have very accurate spectral characteristics, and are uniform, repeatable and calibrated, etc., etc. But hey, what about making a simple LED light source of about the right intensity, maybe crudely replicating the dominate 400 to 750nm region? Or maybe just forget that aspect, and concentrate on a few useful wavelengths?

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 Thanks, 
    - Win
Reply to
Winfield Hill
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You mean as in ~1kW/m^2 and about equivalent spectral characteristics to a 5700K black body (give or take absorbtion lines) ?

There are probably enough 50nm bandwidth LEDs coupled with nominally white ones that you could get something like - but the difficulty would be in mixing them together well enough to get a uniform white.

I suspect these reference sources are expensive for good reason. You might be able to use some standard units with RGBW high power LEDs intended for stage lighting for some applications at close range.

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Regards, 
Martin Brown
Reply to
Martin Brown

Yes.

Yes.

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 Thanks, 
    - Win
Reply to
Winfield Hill

If you would say what you want it for, then we could decide whether different things are good enough to be worth suggesting for that application.

Is it for testing solar cells?

Reply to
Chris Jones

The question is much too vague. Most lighting technologies can approximate sunlight - which set of compromises do you want?

NT

Reply to
tabbypurr

What's the purpose/ application? How about a 5500K incandescent bulb? (I'm not sure they make such things.)

George H.

Reply to
George Herold

They're impossible, unless you go for microwave excited plasma - I don't remember what temps sulphur lamps run at.

NT

Reply to
tabbypurr

Right.. my bad. (Tungsten melts at ~3600K) Arc lamp? I was at a university where they had a mirror (or something) on the roof and could reflect an image of the sun down a long tube into the laboratory.

George h.

Reply to
George Herold

Simple answer, yes. More complex answer - we're also playing with various chemical and electro-chemical solar-conversion schemes. We have access to a proper "one sun", across town, but it'd be useful to have something to play with on the bench. Could be pulsed mode.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

I think if you look at the solar spectra as a function of frequency (energy) you'll find that there is a lot of energy below the visible wavelengths. Here's one,

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George H.

Reply to
George Herold

produce at best 1000 lm, thus a single LED would be capable of

In practice, you will need much more to have a good spectral accuracy.

Of course lm and lx are units depending of human sensory response, which is different compared to silicon solar panels or other biological processes (such as photosynthesis).

Reply to
upsidedown

Here's one that seems to be made from 150w halogen lamps bulbs:

Here's a home made sun simulator that's looks small and fairly cheap:

What I did was search Google Images for photos of "sun simulator" and look through the pictures for anything that looks reasonable. However, I couldn't find anything small and/or cheap.

The one's I've seen use halogen or xenon lamps. LED's tend to have big spectral peaks at a few points, and very little in between, such as in the common "white" LED. You can't adjust that with a few filters.

How about making life easy and just get a few grow lights? Just ask the local indoor marijuana growers for their favorite brands. Most likely, they'll recommend a full spectrum 380 to 840nm LED, which is allegedly used for indoor hydroponics flowers. You could probably fund this project with the proceeds from the sale of agricultural products, but I suspect the administration might ask for a percentage.

Drivel: My copy of AoI has finally made it to the left coast and is now "in transit". If I disappear for a few days, you can guess what I'll be reading.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Skylight and a light meter? Seriously - fiber optic bringing light in light meter to calibrate the results. Not great but maybe useful if the alternative is a trip across town.

Reply to
David Eather

gy)

olor-of-the-sun/

As those spectra show, the atmosphere removes a lot of the XUV bit not al l of the near UV. That's harder to simulate (especially with a single OTS L ED) and will affect materials selection.

I'm slightly surprised that Sun-equivalent LEDs (UV LEDs with phosphors t o generate the Earth-surface daylight spectrum) aren't marketed for people with SAD or for general natural-equivalent indoor lighting. Maybe after the Feds finally take marijuana off Schedule 1?

Mark L. Fergerson

Reply to
Alien8752

On Tuesday, November 1, 2016 at 11:22:15 AM UTC-7, snipped-for-privacy@downunder.com w rote:

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As far as brightness per die is concerned, the wife and I went to a Kitch en Connection store to get something, and they had a bunch of "disposable" LED flashlights in the impulse-buy racks. They were extremely bright. On in spection they proved to use a LED with a relatively huge die without the us ual cast plastic magnifying lens. The die was nearly a quarter-inch across!

They took three AAA cells. They were labeled claiming the LEDs were good for thousands of hours, but I'd be surprised if the batteries lasted an hou r.

Mark L. Fergerson

Reply to
Alien8752

I thought that grow lamps were deliberately depleted of green, since the plant reflects rather than absorbs that?

Reply to
Clifford Heath

Here in Seattle, the light meter tells me 'one sun' is 5W/square meter.

Reply to
whit3rd

yep

Reply to
David Eather

You need to use it in a location without clouds ;D

Cheers

Reply to
Martin Riddle

Yep. The absorption spectrum of chlorophyll has a big hole in the green 500-600 nm area: "Why do some plants appear green"?

I don't know why it's called 380 to 840 nm "full spectrum" LED's. It's not that "full" as there are gaps in various places: "... full spectrum is not a scientific term but it is used to help buyers understand that the lights they are buying

of light right through the visible spectrum."

The McCree Curve is the spectra that plants prefer. I would have expected a big hole in the green area. Instead, there's only a slight dip: The "full spectrum" grow light looks something like the McCree curve, but with a much bigger dip in the green area. Good enough for growing controlled substances, but probably not very useful for testing solar cells especially if repeatability and calibration are important. A sodium light is probably better:

I'll do some more reading, but this is the best I can do with my limited knowledge of plants.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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