Color changing LEDs
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From: mister_friendly on 6 May 2010 02:20 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.
From: D Yuniskis on 6 May 2010 02:51 mister_friendly(a)the-newzgroups.com wrote: > 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)
From: Phil Allison on 6 May 2010 03:44 <mister_friendly(a)the-newzgroups.com> >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? ** 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
From: Cydrome Leader on 6 May 2010 11:21 Meat Plow <mhywatt(a)yahoo.com> wrote: > On Thu, 06 May 2010 01:20:36 -0500, > mister_friendly(a)the-newzgroups.comwrote: > >>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. > > 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.
From: D Yuniskis on 6 May 2010 14:10
Cydrome Leader wrote: > Meat Plow <mhywatt(a)yahoo.com> wrote: >> On Thu, 06 May 2010 01:20:36 -0500, >> mister_friendly(a)the-newzgroups.comwrote: >> >>> 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. >> 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? http://www.pentairpool.com/pdfs/IntelliBriteLEDLandscapeOM.pdf > 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. |