Luminous efficacy describes the efficiency of converting electrical power into visible light. Which statement is true?

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Multiple Choice

Luminous efficacy describes the efficiency of converting electrical power into visible light. Which statement is true?

Luminous efficacy is about how much visible light you get for each watt of electrical power used. That means it compares light output (in lumens, which reflect perceived brightness) to power input (in watts). So the true description is lumens per watt, which directly expresses this efficiency. The other ideas don't fit: lumens per square meter is lux, a measure of light on a surface rather than efficiency; joules per second is watts, a measure of power itself; watts per lumen would be the inverse of efficiency and doesn’t describe how effectively power becomes light.

Luminous efficacy is about how much visible light you get for each watt of electrical power used. That means it compares light output (in lumens, which reflect perceived brightness) to power input (in watts). So the true description is lumens per watt, which directly expresses this efficiency.

The other ideas don't fit: lumens per square meter is lux, a measure of light on a surface rather than efficiency; joules per second is watts, a measure of power itself; watts per lumen would be the inverse of efficiency and doesn’t describe how effectively power becomes light.

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