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.
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.
... Phil
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.
It could be the plastic windows on those cheap things turning yellow?
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Says it all.
They could be RGB leds. These devices, now very cheap on ebay, are externally identical to an ordinary two pin led though they contain three emitting diodes in the same package plus a small circuit that flashes each of them independently.
And you point is what?
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