deskthority

Are there any particular electrical specs to be aware of when choosing replacement LEDs for common lock lights?

Make sure you get ones for the correct voltage. Outside of that, most keyboards aren't too picky.

There are always exceptions though and I'm sure you'll get a giant list of them in here soon.

Thanks - so I guess as long as it's less than 5v, it should be fine? Does the "forward current" parameter matter?

I was thinking purple or blue for color!

The forward current parameter does matter, but I doubt it will be an issue. The forward voltage they are rated at is (oversimplification) the voltage they will use when begin to flow current. In a keyboard there will most likely be an resistor to limit the current (you can think of it as using up the extra voltage). A good rule of dumb that I use to set the current for LEDs is (supply voltage (in a keyboard likely 5 V) - the LED's voltage) / inline resistance should be less than the max forward current.

If you want an even simpler rule of dumb (and an even bigger oversimplification) voltage of Voltage of IR LED < Red LED < Amber LED < Yellow LEDs < Green < Blue < White.
*** This is in general not to be taken as gospel ***

So, in general if you replace a lower voltage LED with a higher voltage LED you won't break anything because the current will be lower (worst case the LED will be a little dim). If you replace a higher voltage LED with a lower one you should check what the resulting current will be.

It is also a good idea to keep in mind how much current will be used overall by the board. If you're just changing the lock lights you can probably ignore the total current because the difference will be small, but if you're doing something like all the backlights on a board then it would be a good idea to think about the total current draw of all of the LEDs combined. It's pretty safe to assume that a USB port can supply 500 mA. If you're going anywhere near that then you should be careful.

Ideally, you would always simulate/calculate what the current would be and then choose an LED accordingly, but who has time for that . If you want an easy circuit simulator that works in browser I'd recommend Falstad.

tl;dr:
If you swap a warmer color LED for a cooler color you will probably be fine but it might be a bit dim. If you do the other way around you're still probably fine, but you might have to increase the current limiting resistor.

****Edit:
Just about every generic LED that I've ever seen has been good up to 20 mA and that should be enough to drop in for just about any other since companys rarely configure their circuits to push the max current. Even if you go over that, the LED will be fine for quite a while but will have reduced life. The reduction in life is proportional to how far over the maximum forward current.

Thanks for the brilliant post!

So blue LEDs and white LEDs take up more power? Makes sense, given how excessively damn bright they are. I thought it was just an efficiency thing.

The longer wavelength colours—red, amber, yellow—are so much easier on the eyes. I suppose a simple swap from a modern blue to a modern red LED would drive the red real bright. Hmm.