Question:easy

The candela is one of the seven base units in the SI system. Which physical quantity does the candela measure?

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Candela is one of the seven fundamental SI base units, and it is specifically tied to how bright a light source appears in a chosen direction.
Updated On: Jul 16, 2026
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Solution and Explanation

Another way to fix this idea in mind is to compare candela with the other light related units so the difference stands out clearly.
  • Luminous flux, measured in lumens, tells us the total quantity of visible light energy given out by a source per second, in every direction.
  • Luminous intensity, measured in candela, narrows this down to how much of that light is sent out in one specific direction, per unit solid angle. It answers how strong the beam looks if you stand in a chosen direction from the source.
  • Illuminance, measured in lux, tells us how much light actually falls on a surface, which depends on both the luminous intensity of the source and its distance from the surface.
  • Among these three, only the candela is a fundamental SI base unit. Lumen and lux are both derived from the candela together with the geometric units steradian and square metre.
This confirms that candela is the base unit for luminous intensity specifically.
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