Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.

On Feb 14, 10:21 am, "HK" wrote:
I'm trying to help my daughter with a school project and while I know my way
around house wiring, I'm a relative newbie when it comes to low voltage.

Let's say I have a 6 volt DC power supply (4 "C" batteries). If I want to
drive a small motor and some lights, I just find 6 volt motors and lights
and wire them in parallel or series.

Why is it that I can't light up a 12v light with a 6 volt power supply? I
always test my batteries using a multi-meter and as the battery ages, the
voltage drops. With low voltage, the device (flashlight, etc.) still works
but the light is weak. So, wouldn't a 12v light just be weak if I use a 6v
power supply?