Howdy Yall, First time poster, long time lurker. I am working on a project right now measuring the "useful" life of a battery...say a AA battery. To relate that to a real world application, I will be powering a light (LED) off the battery. I was initially planning on getting the battery, an LED (unknown specs yet) and a resistor....say 5 ohms. I will be timing how long it takes that LED to "go out". The problem is, what is "go out"? I need to be able to quantify that. Is there a good, CHEAP way to measure light output (intensity?) quantitatively? How about designing a circuit that would cut the LED off when the battery dropped below 0.75 V? That would also work. Any help would be appreciated!