If you reduce the voltage to a light bulb what are the expected results ?

Question

If you reduce the voltage by 8 volts going into a 120 volt light bulb what does it do to the energy consumption and the life of the bulb ?

Answer 1

The power consumed with be reduced by 13%. (112/120 squared = 87%).

The light output will go down more than 13%. About 25-30%.

The bulb life will go up a lot. Two or three times. This is a common trick for hard to reach bulbs - use 130-volt rated bulbs (they're out there) run at 120 volts.

The "color temperature" will be cooler, more yellow and red, less blue. More like sunset, less like mid-day.

You will NOT save energy (for a given light output). If you need 25% less light, use a 75 watt bulb instead of a 100 watt. Or 55w instead of 75w, etc.

Making a $0.50 bulb last longer doesn't help anyone if you use the $12 of electricity (over the 100 hour life of a 100 watt bulb) less efficient at a lower bulb temperature. (Except for those hard-to-reach, labor-intensive locations).

Answer 2

So "normal" bulbs basically run using a resistive filament..
I say "normal" because many bulbs nowadays use the incandescent type design.

Anyway, by reducing the voltage to the bulb, you would simply get a dimmer glow. If you reduced it enough, the bulb wouldn't light at all, but 8 volts is well within that treshold.

Power used = VI Where I = V/R or Power = V^2/R

So by reducing your voltage by 8 out of 120, and assuming same R, you get:

Pnew/Pold = 112*112/(120*120) or Power = 87% of original power used.

Theoretically it also lengthens the life of the bulb since it's burning less hot.


For the new fangled incandescent type bulbs, there's a higher chance that the voltage drop won't allow the bulbs to light up at all, because they require a minimum voltage to strip the electrons from the ions to form a plasma.

Answer 3

The colour of the light also changes with the current through bulb.
At a lower applied voltage, and hence current, the colour will become a little more yellow. Reduce the current still further and the light goes more towards red.

Answer 4

This scheme is barely used in applications the position length requirement can no longer discover the money for using a transformer. however the present requirement is sacrificed subsequently output contemporary ability is barely interior the order of a few mA. So jointly with your required contemporary and voltage, you already may have an theory of ways a lot voltage you should drop from 240. Then remedy for the minimum ability score of the resistor to face up to the heating results of the present flowing by ability of plus a particular safe practices margin perchance.this continues to be Ohms regulation.

Answer 5

Forget about this and use fluorescent bulbs. There's the energy saving, not lowering the voltage.

Answer 6

For an incandescent lamp, you will reduce the energy consumption slightly, the light output considerably, and increase the lifetime of the bulb by roughly a factor of 2. Do not do this with fluorescent lamps -- you may get premature lamp failure or other problems.