More colors from normal leds???

[gregted]

Hi,
I was working on a model train light circuit using leds and a curious thing happened. At one point, there was a short of some sort in the circuit and the green led was showing a distinct yellow indication.

I have not been able to duplicate the fault and was wondering if you can tell me how this might have happened.

I am also wondering what other colors might be extracted from so called normal colored leds, using a similar method.

Any help appreciated.

Greg.

 

[pc88]

I'm guessing you were running too much current though the LED. I don't think much variation in color is possible using this method, and also, your LEDs won't last very long.

 

[Krumlink]

Green Leds usually run on voltage of about 1.7V. you might of accidently shorted out the resistor and the full voltage got through to it. Be careful and make sure you cover up your leads and wires on the reverse side. I put electrical tape on the back of my circuit boards to prevent just that. Whenever I dont put tape on it, It awlays shorts out somewhere, so be careful!

 

[audioguru]

If you want 3 colors then use an ordinary red-green LED.
If you want millions of colors then use an RGB LED or make your own with red, blue and green LEDs.

 

[Krumlink]

I prefer milky or hazed LEDs. If you get waterclear RGB LEDs you can see the Dies clearly and it kind of ruins the mixing color effect.

 

[Oznog]

Could be a "bicolor" LED. Green when current goes in one direction, red in the other, AC make red and green which blends into yellow in the human eye.

 

[Sceadwian]

That yellow colour was the diode junction starting to act like a regular lightbulb. You can only do that a few times before you end up with a piece of useless plastic. LED's are capable of producing only a single colour of light.

 

[j.p.bill]

LED's do have tha ability to give a little spectral variation. The more energy through the LED, the higher frequency of light they give off. I don't know what the range is, but you can push more current through the junction and shorten the wavelength by more than 20 nM. Obviously, too much current and the LED dies.

The color change is exploited by chemists as a sensitive probe into some absorbance phenomina.

 

[Gayan Soyza]

At one point, there was a short of some sort in the circuit and the green led was showing a distinct yellow indication.

Its normal.When you give 2V it might light up with the colour it has green.But see after increasing the voltage to the green LED,it will change its colour to yellow.If you still continue giving more voltage than rated voltage you will see nothing from few minutes but you will feel a bad smell.

Super Green Mat LED is best for me.

 

[Krumlink]

I fed 36V at about 500ma (model train power supply, now dead ) into a LED real fast and it exploded into flames, sending flaming chunks of plastic everywhere. Ouch. It was pretty awesome though.

 

[Hero999]

LED's do have tha ability to give a little spectral variation. The more energy through the LED, the higher frequency of light they give off. I don't know what the range is, but you can push more current through the junction and shorten the wavelength by more than 20 nM. Obviously, too much current and the LED dies.

The color change is exploited by chemists as a sensitive probe into some absorbance phenomina.

What you're saying is true but that wasn't the case here as yellow is a longer wavelength than green.

I read somewhere that it's possible to get some blue LEDs to emit UV by pulsing them at very high currents but I've never tried it, I think you need a specific kind of blue LED.