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# Brightness of light bulb

I was working through some questions on DC Circuits. I am confused as to on what factors does brightness of a light bulb depends.

For a bulb with given voltage and power, on what factors would its brightness depend? Suppose we increase the voltage more than labeled on it; would the brightness decrease, increase or remain the same? Likewise, what would happen if we decrease the voltage?

I am totally confused regarding the factors on which brightness of bulb depends. Further why do we use different bulbs if brighness of a bulb can be controlled. I would be grateful if someone could explain this or provide an online source relevant to the understanding of this topic.

Bulb 1 is labelled as 60W, 120V and bulb 2 is labelled as 120W, 120V. Which one would be more bright when connected in series and parallel?

This is what I think about the problem:

The resistance of both bulbs are respectively, 240 ohm and 120 ohm. Since the current is same in series. The power dissipated would be more in bulb 1. Bulb 1 would be more bright in this case. When the bulbs are connected in parallel, the power dissipated would be more in bulb 2. Bulb 2 will more bright in this case.

Note by Lokesh Sharma
3 years, 9 months ago

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Its correct · 3 years, 3 months ago

I think voltage doesn't necessarily correlate with the brightness of a bulb. This can be proved as follows: We get some bulbs of different ratings such that their resistances are different.On connecting them parallel to a battery,they take up the same voltage but their brightness differs. · 3 years, 9 months ago

Okay... Thanks · 3 years, 9 months ago