What Voltage for Led's?

[jimhaleyscomet]

I ordered in the following LED kit from
http://www.mpja.com/productview.asp?product=16313+OP

Does anyone know if there is a "standard" voltage for LED's?

110 Pcs. LED ASSORTMENT KIT

110 Piece, LED assortment packed in a plastic divider box, contains: 5pcs. 5mm Hi intensity White;10ea. of the following: 5mm red, green, yellow, infrared; 3mm red, yellow and green; 30ea. black mounting clips for 5mm LEDs. Stock No.: 16313 OP

Jim H

[FJ and G]

I would personally start out at the lowest voltage and work my way up until the light comes on. They make cool crackling sounds when the volts are too high. I think they usually come on around 2 volts but they vary and the voltage isn't marked on them

[trigtrax]

LEDS are diodes and rated in foward current and reverse blocking voltage. Use a battery or low voltage DC suppy with at least a 470 ohm resistor in series to test them.
Usual numbers are 20 mA current and 5 volts or less. MPJA is a surplus supplier, they buy overstock in bulk and I've usually gotten decent stuff from them.

[jefelectric]

Here are a couple of web sites that have basic LED info.

http://www.theledlight.com/technical.html

http://www.redcircuits.com/Hobby.htm

[lionelsoni]

The forward voltage increases across the spectrum from about 1.5 volts for red to about 3.5 volts for blue. (White LEDs are really blue LEDs with some phosphers to convert some of the blue to the other spectral components of white light.) Use a ballast resistor and a DC supply at about twice the forward voltage. Do not put any significant reverse voltage across the LED.

[wrmcclellan]

White LEDs have a very low reverse voltage characteristic (as low as 5 volts). To improve reverse voltage protection, white LED manufacturers recommend use of a regular diode (e.g. a 1N4001) in series with the whilte LED. The additional diode provides the necessary reverse voltage protection and then you can power the white LED/diode/ballast resistor combination with AC voltage.

I have been running several using a cheap 1N4148 diode and a 560 or 620 ohm resistor for over a year continuously at 16 volts AC.

[lionelsoni]

A little trick for AC operation is to put two LEDs in parallel, cathode to anode, so that each one protects the other from reverse voltage. And you get twice the light for the same power, pretty much.

[darianj]

QUOTE: Originally posted by lionelsoni

A little trick for AC operation is to put two LEDs in parallel, cathode to anode, so that each one protects the other from reverse voltage. And you get twice the light for the same power, pretty much.

HMMM...I'll have to try that.