At 04:36 AM 8/20/2005 +1000, you wrote:
>PICers - just curious about "White LEDs" that you see in the catalogues. Are
>they truly broad spectrum white-light, as in daylight or from a fluoro 
>tube? Or
>is it some trick they do by combining narrow band R,G,B emissions?
>Thanks - Debbie :)

Typically, they use a phosphor and a blue LED die to get white-ish light.

The spectrum is more like that of a fluorescent tube-- multiple peaks, and
nothing at all like that of incandescent light or sunlight.  Many mfrs.
don't publish information on the spectrum. Some are much more blueish
than others, and the color often varies depending on the angle off the
axis.

Here's a Toyoda-Gosei datasheet showing the spectrum of their white LEDs:

http://www.toyoda-gosei.com/led/products/pdf/E1L35_xWxxx_JEA.pdf

You can see a strong narrow peak at around 470nm (blue) and another softer
peak at around 575nm (yellow), with a tail extending up into red
wavelengths.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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