What is the Difference Between Light Source and Illuminant?

The main difference between a light source and an illuminant lies in their definitions and applications. Here are the key distinctions:

• Light Source: A light source is any object that emits visible light, such as the sun, stars, light bulbs, and semiconductor diodes. The quality and energy of the light are not described or defined in any way, and it can vary depending on the source. Light sources are often used in photography and other fields where light is essential.
• Illuminant: An illuminant is a representation of a light's spectral power distribution curve in graph or numerical form. It is not a physical object but rather an artificial construct used to describe the spectral quality of a specific type of white light source. Illuminants are typically used in color measurement and other applications where the spectral quality of light is crucial.

Some common illuminants are standardized by the Commission Internationale de L’Eclairage (CIE) and include incandescent or tungsten light sources (A, 2856° Kelvin), cool white fluorescent light sources (F2, 4000° Kelvin), and others. These illuminants are used to evaluate color appearance and accuracy in various industries, such as photography, textiles, and automotive.

In summary, a light source is a physical emitter of radiation, while an illuminant is a representation of the spectral quality of a specific type of white light source. Both concepts are essential in fields related to light and color measurement.

Comparative Table: Light Source vs Illuminant

The difference between a light source and an illuminant lies in their definitions and applications. Here's a table summarizing the differences:

A light source is a physical emitter of radiation that can be characterized by a spectral power distribution curve, showing the power at each wavelength in the visible spectrum. On the other hand, an illuminant is a set of numbers representing the spectral quality of a type of white light source, providing a standardized reference for color evaluation and comparison. The CIE (Commission Internationale de L'Eclairage) has defined various illuminants based on their spectral information, such as incandescent/tungsten lamps (Illuminant A) and fluorescent lamps (Illuminant F).