WHITE LED Question

[chicago_mike]

I have a bunch of white LED's.

Clear 5mm and if you look straight at them, theres a white backing to it....you can't see that otherwise.

are these UV?? They almost...almost look purple, but they are white. White is close to purple in the spectrum right?

Thanks!

[darron]

white isn't in the spectrum, it's a combination of all the colours. here... let pink floyd explain:








but why not plug it in and see what colour it is?

UV isn't in the visible spectrum. it's that light we can't see that gives us cancer on an overcast day.

the "ultraviolet" LEDs they sell that we can see should be called "very violet" ... or.. something...

[Gurner]

A white LED is actually a blue LED coated with yellow phoshor to absorb the blue and sort of 'blag' a white result  - so perhaps you're seeing a blue/yellow mix, which when unlit probably won't appear mixed in the right proportion....

[CynicalMan]

White light is usually composed of the entire colour spectrum, as Pink Floyd shows. Sunlight is like that. Incandescent lights are somewhat like that, but if you look at their spectrum they're slanted towards the red side, which gives them their yellowish look. White LEDs are different, they have a narrow blue peak, and a wider yellow-green peak. The combination of these colours gives the illusion of white light, but it might be why yours don't quite look white.

[chicago_mike]

cool 

[Earthscum]

LED's for different purposes have different ratings, just like your incandescent lighbulbs. A "warm" colored LED will probably emit less UV than an LED that is made for flashlights. The UV enhances our vision. Not too long ago it was getting to be common practice to UV enhance TV's so the picture looked crisper and clearer. Notice dark scenes in movies aren't shot in real black? The black shifts towards blue so your eyes can make out contrast easier. Now they are playing with additional colors instead of the UV enhancement.

Birds and deer and many other types of animals have higher sensitivity to UV, and a full moon is just as bright as the sun to them. And ironically, as humans Green is our most sensitive color. Some silly stuff for your brain. 

[Jdansti]

The LEDs we use emit multiple wavelengths (laser LEDs emit one wavelength), and some LEDs emit UV in addition to visible light. I recently bought some hot pink LEDs and there was a warning in the package that said they emitted UV and to not look directly into them.

The UV spectrum (10 nm to 400 nm) is between the visible (400 to 750 nm) and x-ray (0.01 to 10 nm) spectrums.





The best way to know is to look at the data sheet.  Here's an example spectrum from a white LED I found at Mouser:



As you can see, not much happening below 400nm which means little to no UV energy.