Which SI base unit measures luminous intensity?

Which SI base unit measures luminous intensity?

• A. Candela (cd)
• B. Meters (m)
• C. Mole (mol)
• D. Kelvin (K)

Answer: (A)

Luminous intensity is a photometric quantity that describes how bright a light is in a specific direction, taking human vision into account. The SI base unit for this directional brightness is the candela. Luminous intensity, I, is the luminous flux per unit solid angle, so in practical terms one candela equals one lumen per steradian. This ties into related concepts: luminous flux (measured in lumens) is the total perceived light emitted, and when that flux is distributed over a solid angle, the result is the intensity measured in candelas. The candela is one of the seven SI base units, while meters, moles, and kelvin measure length, amount of substance, and temperature, respectively—quantities unrelated to how bright a source appears in a given direction.

Luminous intensity is a photometric quantity that describes how bright a light is in a specific direction, taking human vision into account. The SI base unit for this directional brightness is the candela. Luminous intensity, I, is the luminous flux per unit solid angle, so in practical terms one candela equals one lumen per steradian. This ties into related concepts: luminous flux (measured in lumens) is the total perceived light emitted, and when that flux is distributed over a solid angle, the result is the intensity measured in candelas. The candela is one of the seven SI base units, while meters, moles, and kelvin measure length, amount of substance, and temperature, respectively—quantities unrelated to how bright a source appears in a given direction.