Which of the following terms refers to the intensity of light emitted from a source?

Which of the following terms refers to the intensity of light emitted from a source?

• A. Foot-candle
• B. Footlambert
• C. Candela
• D. Lumen

Answer: (C)

The term that refers to the intensity of light emitted from a source is "candela." The candela is a fundamental unit of measurement in the International System of Units (SI) and specifically quantifies the amount of light produced by a source in a particular direction. It is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 terahertz and that has a radiant intensity in that direction of 1/683 watt per steradian. Understanding the other terms helps clarify why candela is the correct answer. For instance, foot-candle measures illuminance, which is the amount of light that falls on a surface—expressed as lumens per square foot—rather than the intensity of the light source itself. Footlambert also pertains to the brightness of a surface reflecting light and not directly to the source's intensity. Lumen, on the other hand, refers to the total quantity of visible light emitted by a source, without specifying the directionality or intensity in a specified direction like the candela does. Therefore, candela is the direct indicator of light intensity from a source, making it the correct choice for this question.

The term that refers to the intensity of light emitted from a source is "candela." The candela is a fundamental unit of measurement in the International System of Units (SI) and specifically quantifies the amount of light produced by a source in a particular direction. It is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 terahertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Understanding the other terms helps clarify why candela is the correct answer. For instance, foot-candle measures illuminance, which is the amount of light that falls on a surface—expressed as lumens per square foot—rather than the intensity of the light source itself. Footlambert also pertains to the brightness of a surface reflecting light and not directly to the source's intensity. Lumen, on the other hand, refers to the total quantity of visible light emitted by a source, without specifying the directionality or intensity in a specified direction like the candela does. Therefore, candela is the direct indicator of light intensity from a source, making it the correct choice for this question.