Candela is the SI unit of luminous intensity, which measures the brightness of light as perceived by the human eye. When we talk about light, it is not enough to measure how much energy it has. We must also measure how bright it appears to our eyes. For this reason, scientists use the unit candela (cd) to measure luminous intensity.Definition of CandelaAccording to the International System of Units (SI), one candela is the luminous intensity of a source that emits monochromatic light of frequency 540 × 1012 hertz with a radiant intensity of 1/683 watt per steradian.Key Features of CandelaSI Base Unit: Candela is one of the seven base units in the SI system.Represents Brightness: It measures perceived brightness, not just energy.Human Eye Sensitivity: It is defined according to the sensitivity of the human eye to green light.Examples of Candela in Real LifeA standard candle emits roughly 1 candela of luminous intensity.A flashlight might emit 50–200 candelas.A car headlight can be 15,000 candelas or more.Relation with Other UnitsCandela is related to lumen (lm), which measures luminous flux. One candela equals one lumen per steradian. While lumen measures total light output, candela focuses on intensity in a particular direction.

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What is candela?

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Detailed Solution

Candela is the SI unit of luminous intensity, which measures the brightness of light as perceived by the human eye. When we talk about light, it is not enough to measure how much energy it has. We must also measure how bright it appears to our eyes. For this reason, scientists use the unit candela (cd) to measure luminous intensity.

Definition of Candela

According to the International System of Units (SI), one candela is the luminous intensity of a source that emits monochromatic light of frequency 540 × 10¹² hertz with a radiant intensity of 1/683 watt per steradian.

Key Features of Candela

SI Base Unit: Candela is one of the seven base units in the SI system.
Represents Brightness: It measures perceived brightness, not just energy.
Human Eye Sensitivity: It is defined according to the sensitivity of the human eye to green light.

Examples of Candela in Real Life

A standard candle emits roughly 1 candela of luminous intensity.
A flashlight might emit 50–200 candelas.
A car headlight can be 15,000 candelas or more.

Relation with Other Units

Candela is related to lumen (lm), which measures luminous flux. One candela equals one lumen per steradian. While lumen measures total light output, candela focuses on intensity in a particular direction.

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