# Brightness of Lightbulb

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#### fuzzywuz

##### Full Member
10+ Year Member
5+ Year Member

Hey all,

I could use some advice on this topic.

What determines the brightness of a lightbulb? (Resistance, current, power?)

I remember when I took physics, for the circuits lab, we had to predict what would happen to the brightness of the bulb depending on how we manipulated resistors in the circuit (e.g. if we removed one resistor that was in parallel or in series) and other scenarios as well.

Can anyone point me in the right direction regarding this topic since there isn't much in the review books or textbooks.

Thanks!

#### engineeredout

##### Full Member
10+ Year Member
The light from a standard halogen lightblub is caused by resistance in the tungsten filament causing it to not only glow (light) but to give off an enormous amount of heat, which is the reason for the high inefficiency of halogen bulbs.

And yeah power is related through the same reason. Power = I^2 * R. Greater R = Greater power needed.

Thats cool that you got to play with circuits in physics lab. The most we did having to do with electricity was using an oscilloscope.

#### HawkeyePostOp

##### the fort at sidewalk
10+ Year Member
5+ Year Member
For the MCAT, only power determines the intensity of a lightbulb. You probably know it all. Just analyze the circuit and see if power output of the lightbulb changes with the new conditions.

If you put the resistor in series, the overall resistance of the circuit increases, decreasing the current, thus decreasing the power output and intensity of the bulb. If you put a resistor in parallel, output can vary or stay the same depending on the resistor.

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