LED tester/current thingy...

[tramcar trev]

For $2.65 this is a ripper, lets you see how a led performs under various conditions before you go through the routine of wiring it in as a headlight or whatever....

http://www.ebay.com.au/itm/K1BO-Min...cal_Test_Equipment&hash=item3f291a520e&_uhb=1