Do you have a button type cell powered light?

[Teofilo]

[Benner]

Nope. 

[edap617]

That's sweet liitle light gene!

I only have two very simple button cell lights.

[jock1]

I have exactly the same one great ain't they

[Energie]

Homemade button cell light (10 years old)
and a super modern lighthound fauxton 

[Teofilo]

A home made button cell light! That's great energie! Actually I don't know the runtime of these button cell lights. Any idea, guys?

[Energie]

Actually I don't know the runtimes of these button cell lights. Any idea, guys?

Depends on the cell.
For example:
Current to the (white) led 20 mA, Vf 3,4 V
Direct drive with resistor (no driver)
used cell:  2 * lithium CR2025  (= 6V, 140 mA)
runtime approx. 3-4 h (dimming)

Better results with a small driver: PR4401 
(German site:http://www.ak-modul-bus.de/stat/led_treiber_pr4401.html)