But the light output goes down with at least as strong a function, I
believe. So although you can greatly extend the life of a bulb by
reducing the voltage, you also greatly reduce the light output. And
without nearly as much of a reduction of the input power. So you end up
with a dim, very inefficient bulb. That might be ok for some
applications (say, if it's at the top of a tower where it's a really
major pain to change) but not others (like all the bulbs in your house,
unless you love to pay that electric bill).

Roy Lewallen, W7EL

Robert Casey wrote:

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs
myself....