A light bulb emits 60 lumens and consumes 60 watts. What is its luminous efficacy?

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Multiple Choice

A light bulb emits 60 lumens and consumes 60 watts. What is its luminous efficacy?

Luminous efficacy is how bright a light is per unit of power, measured in lumens per watt. So you divide the light output by the power used. For this bulb, 60 lumens are produced while consuming 60 watts, giving 60 ÷ 60 = 1 lumens per watt. That’s exactly what the option stating 1 lm/W describes. The other options mix up the ratio or use the reciprocal concept (watts per lumen), which doesn’t match this bulb’s performance.

Luminous efficacy is how bright a light is per unit of power, measured in lumens per watt. So you divide the light output by the power used. For this bulb, 60 lumens are produced while consuming 60 watts, giving 60 ÷ 60 = 1 lumens per watt. That’s exactly what the option stating 1 lm/W describes. The other options mix up the ratio or use the reciprocal concept (watts per lumen), which doesn’t match this bulb’s performance.

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