The SI unit of luminous intensity is the candela , which is a primary unit. The derived SI unit of luminous flux is the lumen (abbreviated lm). These are based on the sensitivity of the human eye to light. Light sources are often evaluated based on their luminous efficacy, which is defined as the luminous flux divided by the power consumed and is measured in lm W−1. In a physical or online store, find manufacturer’s specifications for representative incandescent, halogen, high-temperature-discharge, LED, and fluorescent lamps of similar luminous flux and compare their luminous efficacy.

The unit of luminous intensity is candela, amount of substance mole, thermodynamic temperature Kelvin, electric current ampere....

The Candela is the unit of Luminous intensity.

- Luminous intensity is a measurement of the amount of light emitted in a particular direction from a light source. It quantifies the brightness of the source as perceived by the human eye. The Candela (cd) is the SI unit for luminous intensity.

Explanation:

Luminous intensity is a fundamental quantity in the field of photometry, which is the science of measuring light in terms of its perceived brightness to the human eye. It is different from radiant intensity, which measures the total power emitted by a light source in all directions, regardless of human perception.

The Candela is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation with a frequency of 540 terahertz (THz) and has a radiant intensity in that direction of 1/683 watt per steradian.

The Candela is based on the sensitivity of the human eye to different wavelengths of light. The wavelength of 540 THz corresponds to the peak sensitivity of the human eye, which is in the green-yellow region of the visible spectrum.

The unit is named after the Latin word "candela," which means candle. The choice of the name is historical, as candles were often used as a reference for measuring luminous intensity in the past.

The Candela is used to measure the brightness of various light sources, such as light bulbs, LED lamps, and lasers. It is an important metric in lighting design, as it helps determine the appropriate level of illumination for different applications, such as indoor and outdoor lighting, automotive lighting, and stage lighting.

In summary, the Candela is the unit of luminous intensity, which quantifies the brightness of a light source as perceived by the human eye. It is an essential measurement in photometry and is used to evaluate and standardize the brightness of various light sources.