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?

Is there some kind of voltage threshold at which a device won't work?

Like I said, basic question.

I haven't read the rest of the responses yet, so I'll just say some
dumb stuff until somebody explains to me I'm an idiot.

First: heat is related to wattage through bulb. wattage is
proportional to voltage squared, so at half voltage you get one
quarter the wattage therefore one quarter the heat produced, all else
being equal (which it never is).
Temp vs. heat.... umm, i think that's more or less linear, so half the
voltage means one quarter the wattage means one quarter the heat means
one quarter the rise in temp over room temp.
Now the fun.... the radiated energy vs temp follows the black body
equation, which relates the energy at each wavelength to the
temperature and is best explained by your looking here http://
hyperphysics.phy-astr.gsu.edu/hbase/bbrc.html#c1 rather than me
trying to reproduce it in words. You see that the intensity,
particularly at visual light, falls off real quick as the temp falls
off.