The unit of lamp efficiency is a measure of how effectively a lamp converts electrical power into light. The correct unit for lamp efficiency is lumens/watt. Let's understand this and discuss why the other options are incorrect.
- Lumens/watt:
- This is the unit of luminous efficacy, which is a measure of how effectively a light source produces visible light from electrical power.
- \(\text{Luminous\ Efficacy} = \frac{\text{Lumens}}{\text{Watts}}\)
- The higher the lumens per watt, the more efficient the lamp is in converting electrical energy into light.
- Lux:
- Lux is a unit of illuminance, not lamp efficiency. It measures the amount of light (luminous flux) hitting a surface per unit area.
- 1 lux equals 1 lumen per square meter.
- Foot candle:
- This is also a unit of illuminance used mainly in the United States, equivalent to one lumen per square foot.
- It does not represent lamp efficiency.
- Lumen:
- Lumen is a measure of total visible light emitted by a source (luminous flux), not efficiency.
- While it indicates the light output, it does not directly describe efficiency as it lacks reference to power input.
Therefore, the unit of lamp efficiency, specifically luminous efficacy, is correctly expressed as lumens per watt. This considers both the luminous output (lumens) and the electrical power input (watts).
Important Questions from Illumination
Silicon solar cell has an open circuit voltage NOT equivalent to-
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Light is produced in electric discharge lamps by
________ lamps consist of an inner discharge tube and an outer evacuated tube.
A mercury vapor lamp gives ______ light.
