• Lumen (i.e. lm) is the unit of luminous flux. Luminous Flux normally refers to the luminance of projector.
• Luminous Flux is a measure of the total quantity of visible light emitted by a source per unit of time. Also known as the light energy absorbed by an illuminated object per unit of time.
• Lux (i.e. lx) is the unit of illuminance.
• Illuminance refers to a measure of how much luminous flux is spread over a given area.
Luminous Flux measures the total "amount" of visible light present, while the illuminance measures the intensity of illumination on a surface.
One lux is one lumen per square meter. Mathematically, 1 lux= 1 lm/m2
For example: A flux of 1000 lumens, concentrated into an area of one square meter, lights up that square illuminance of 1000 lux. However, the same 1000 lumens, spread out over ten square meters, produces a dimmer illuminance of 100 lux.
Luminance (lumen) = illuminance (lux) * screen area
For the same projector with fixed Luminance (lumens), the larger the projected area, the less illumination it produces; Vice versa, the smaller projected area, the more illumination it assembles.