Illumination refers to the amount of visible light that falls on a surface per unit area. It is often measured in units called "lux" or "lumens per square meter." Illumination is an important concept in lighting design and engineering, as it affects how well we can see and perceive objects in a given environment.
Lumen, on the other hand, is a unit of luminous flux, which measures the total amount of visible light emitted by a light source per unit of time. In simpler terms, lumen quantifies the brightness of a light source. The more lumens a light source emits, the brighter it appears to the human eye.
The relationship between illumination (lux) and luminous flux (lumen) is influenced by the distance between the light source and the surface being illuminated. As light travels outward from a source, it spreads out, resulting in a decrease in the illumination on a surface the farther it is from the source.
In summary:
Illumination (lux) is the amount of light falling on a surface per unit area.
Luminous flux (lumen) is the total amount of visible light emitted by a light source.
The brightness perceived by the human eye is determined by the number of lumens emitted by a light source.
To achieve a desired level of illumination in a given area, factors such as the light source's luminous flux, the distance between the source and the surface, and the reflective properties of the surroundings all need to be considered in lighting design.