If I was making a PC case, and I wanted to put my own LED in for the hard disk drive indicator, would that LED need to be a specific voltage LED? At rat shack I can buy LEDs in 2.1v, 5v, and 12v.

<emily litella> Never Mind. </emily litella>

(2.1v works fine)

For reference...

The forward voltage of an LED is an attribute of the semiconductor used to create it, as is the color of the LED. So most LEDs of the same color will have the same forward voltage, as they will mostly be using the same (cheapest to manufacture) semiconductor material.

This voltage is typically 1.7V for red, 2.1V for yellow and 2.2V for green. (All 'standard' LEDs not 'high efficiency' or 'super-bright'). These 'traditional' LEDs have forward voltages so close together that in the vast majority of applications where the output brightness is not required to be calibrated, engineers would simply use 2V as the forward voltage when calculating the series resistance. ( R=(Vsupply-Vforward)/ Iforward ). For a typical Iforward of 10mA this worked perfectly fine.

Newer developments have created LEDs with a wider range of Vforward. Blue and white LEDs are typically 4V or more, so that rule of thumb can't be used for all LEDs anymore.

There are no 12V LEDs. When you see something labelled as such, it is really a standard voltage LED with a built in series resistor calculated for a supply voltage of 12V. Such items are convenient for indicators in automotive and marine environments, which is exactly why they are made.

A PC motherboard has the series resistance built in. I'm not sure whether the ATX specs defined the colors used for the power and HDD LEDs or not. But I'd bet that most of the engineers used the 2V value anyway.

Very interesting. Thanks for that information, I didn't know any of that.

I'm using a green LED now, I wonder if a blue one would work?

Good thread.

I'm thinking of having a monitor and keyboard/mouse in the garage of my next home. The case would be on the other side of the wall (and away from the humidy and extreme temperatures of Midwest winters). In addition to the monitor and input devices, I want to have a remote power switch and power LEDs (hopefully as easy as running longer wires and remounting the parts on something). But if I have to wire my own LEDs, this info will come in handy. I just love the idea of being able to research a project while in progress. (What was the torque spec for a 2002 Impreza again?)

Most likely. I replaced the green leds in my case with blue ones and they work without any problems...

Stig