Low current white LED

[wigman27]

Hey all :-)

I am working in a project for a mate, he wants to install a white LED inside a 3mm diameter tube to shine through some little bead type things. Apparently they have really small images inside them.

The size isn't the issue, the problem is he has to use a 3mm diameter battery, which there aren't many of.. One he has found is a lithium cell used in floats, it's a 20mah battery at 2.5 - 3v. The recommended current draw is 500 micro amps.

Does anyone know of an LED that will work well enough at that lower current with a Vf of around 2.5v?

I have found a few but not sure how well they will work that low down.

Thanks :-)

[mikeselectricstuff]

The most efficient LEDs will be white, with high colour temperature.
You will probably need to boost the voltage - you may get a little output at 2.5V, but not much

[wigman27]

Yeah I thought that may be the case, I don't thing I will be able to fit a boost circuit on board so I may need to try and get some shorter batteries and put 2 in series. He is pretty keen to put the shortest amount of tubing possible.

[IanB]

From time to time I have obtained various novelties about the size of a small tie clip or badge with a flashing red LED in them. They use a miniature button cell and a very tiny boost/flash circuit. Red LEDs of course have a low enough Vf to run from a 3 V lithium cell and the flashing circuit dramatically reduces the current consumption.

So something like that might be a possibility? Does it have to be white?