How is luminous intensity measured?

• A. In Joules
• B. In Newtons
• C. In Candela
• D. In Watts

Answer: (C)

Luminous intensity is measured in candelas, which is the standard unit of measure for this quantity in the International System of Units (SI). The candela quantifies the perceived power of light emitted by a source in a particular direction, thereby reflecting how bright that light appears to the human eye.

The importance of the candela stems from its emphasis on human perception of light rather than just the physical properties of light itself. It is directly related to the intensity of light as it is perceived, which is vital in fields such as lighting design and photography, where understanding the visual impact of light is crucial.

Other units, such as Joules, measure energy; Newtons measure force; and Watts measure power (which is related to the rate of energy transfer). Therefore, these units do not apply to luminous intensity, highlighting why the appropriate choice is indeed candelas.