Define luminous intensity and state its unit.

Define luminous intensity and state its unit.

• A. Luminous intensity is the energy emitted by a source measured in joules
• B. Luminous intensity is the total light emitted measured in lumens
• C. Luminous intensity is the brightness of a lamp and it's measured in watts
• D. Luminous intensity is the brightness of a lamp and it's measured in candela

Answer: (D)

Luminous intensity describes how bright a light source appears in a specific direction—it's about the amount of light emitted toward that direction per unit solid angle, not the total energy or total light output. The unit candela (cd) is the SI unit for this directional brightness, defined in relation to a reference light and human eye response. This distinguishes it from energy in joules, total light output in lumens, or power in watts. So the brightness in a given direction is measured in candela, making the described choice the correct one.

Luminous intensity describes how bright a light source appears in a specific direction—it's about the amount of light emitted toward that direction per unit solid angle, not the total energy or total light output. The unit candela (cd) is the SI unit for this directional brightness, defined in relation to a reference light and human eye response. This distinguishes it from energy in joules, total light output in lumens, or power in watts. So the brightness in a given direction is measured in candela, making the described choice the correct one.