Color changing LEDs

 

I keep seeing these little solar power sidewalk lights.  Last year
they were all white (blueish white).  Lately I see them where they
change color.  Yet, they only have one LED.  How can a LED change
color?  I thought the color was determined by dopeing it with a metal.
So how can they change?  This has me puzzled.

 

mister_friendly@the-newzgroups.com wrote:

How do you *know* it is "one LED"?  I suspect it is a "bicolor"
LED (almost a sure bet if it has more than two leads -- still
possible even with just *two*).

You might want to notice the ranges of colors and consider
what color *mixes* could make them (e.g., red + green LEDs in
the same package will yield yellow-ish -- plus variations from
red *to* green depending on the mixing rates)

 




** Bi-colour LEDS like this have been around for 30 years.

http://www.effled.com/images/products/bicolor-led/throughhole-led/3mm_Bin_Color_LED_RG.jpg




...  Phil

 

On Thu, 06 May 2010 01:20:36 -0500,
mister_friendly@the-newzgroups.comwrote:


Bi-color LED have two LED inside with a common cathode. Change the
polarity and you switch on the other LED.

 


this probably has nothing to do with bicolor LEDs. Who the hell would make
a red/green sidewalk light anyways?

Anyways, white LEDs are sort of like flourescent lights. They junction
makes bright blue light and there is a phosphor that then converts this
into "white". Quite a bit of the blue leaks out.

The quality of white can vary (and does so more with cheap LEDs) in
addition to the phosphor actually aging.

so a visible color change from a cheap white LED isn't all that
surprising.