Question

Brightness of light is measured in ____?

Answer 1

Hint: When answering questions like the ones given above, remember the various concepts surrounding light like intensity of light, brightness and darkness, what causes them, what affects them to increase and decrease, their SI units et cetera. Keep in mind the concepts regarding light waves and different frequencies surrounding light.

Complete answer:
The power of light, or how much light energy comes per unit time, is typically sensitive to light-sensitive equipment (like human eyes or film in a camera). However, the total power emitted by a light source is rarely a useful indicator of how bright something is; if the light source moves far enough, much of the light will not reach our target, and the light source will appear dim. Rather, we define intensity as the amount of light that passes through a certain area (in other words, intensity is the amount of energy that arrives per unit area, per unit time). The more concentrated the light that reaches us, the "brighter" it looks.
When we talk about light, we talk about the photons present in it. The brightness of intensity of light is dependent on the number of photons present in it. Photons are energy packets or quanta connected with electromagnetic radiation.
Wavelength, speed, and amplitude are the three qualities of light. The type of light determined by the wavelength (color, etc.). Whether light goes through a vacuum or a substance determines its speed. The intensity of light increases as the number of photons released per unit time increases.
Now coming to our question, brightness is measured now by Candela (\[cd\]) which has replaced a standard lamp or candle as a unit of luminous intensity. One candela is defined as the luminous intensity of a light source in a given direction emitting monochromatic radiation in the frequency of \[540 \times {10^{12}}Hz\] and has a radiation intensity of \[\dfrac{1}{{683}}\] Watt per steradian (\[sr\]) in that direction.
Hence, we can conclude by saying that brightness of light can be measured in Candela (\[cd\]).

Note: When we talk about Candela and photons, another term called Lumen (\[lm\]) comes to mind. It is the unit used to describe the amount of light or luminous flux. The amount of light that streams forth through one steradian from a uniform point source with an intensity of one candela defined as a lumen.