Question

Symbol of luminous intensity is cd
A) True
B) False

Answer 1

Hint: The SI unit for luminous intensity is candela. Candela is one of the SI units of luminous intensity which measures the luminous power emitted per solid angle.

Complete answer:
Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a given direction per unit solid angle, based on the luminosity function which is a standardized model of the sensitivity of the human eye. The intensity is measured using a unit called candela.
The SI unit of luminous intensity is Candela (cd) hence the statement in the question is true. So, option (A) is correct.

Additional information:
The branch of photometry deals with the measurement of visible light as perceived by human eyes. The human eye can only see light in the visible spectrum that includes all the colors we see around us and has different sensitivities to light of different wavelengths within the visible wavelength spectrum. The eye is most sensitive to greenish-yellow light at 555 nanometres wavelength. Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The plot which measures the response of the human eye to light is a defined standard, known as the luminosity function that we discussed in the solution as the standardized model.

Note: Luminous intensity should not be confused with luminous flux, which is the total perceived power emitted in all directions. Luminous intensity is the perceived power per unit solid angle. So, the luminous flux will always be higher than the luminous intensity for any object. Candela is one of the SI base units so we must be aware of it in general.