Lumen, Lux, Candela, Kelvin

Posted by JIT Support

Lumen, Lux, Candela, Kelvin

Basic Lighting Units

Lumen (lm) – Luminous Flux

The Lumen (lm) is the SI unit (International System of Units) of luminous flux. It expresses the total amount of visible light emitted by a light source, as perceived by the human eye.

Luminous flux differs from radiant flux, which measures the total emitted radiation energy regardless of human vision.

The Lumen is defined in relation to the Candela:

1 lm = 1 cd × 1 sr

(sr = steradian / solid angle)

Candela (cd) – Luminous Intensity

The Candela (cd) is the SI unit of luminous intensity. It expresses the intensity of light emitted by a light source in a specific direction.

For example, a common candle emits approximately 1 candela.

1 cd = 1 lm / 1 sr

(sr = steradian / solid angle)

Lux (lx) – Illuminance

The Lux (lx) is the SI unit of illuminance. It is used in photometry to measure the amount of light falling on a surface per square meter.

1 lx = 1 lm / m²

Kelvin (K) – Color Temperature

The Kelvin (K) is used to measure the color temperature of a light source.

Color temperature describes whether light appears warm (yellowish) or cool (white or bluish).

The lower the Kelvin value, the more warm (yellowish) the light appears.
The higher the Kelvin value, the more cool (white or bluish) the light appears.

Due to the different materials used in their construction, light sources emit light with different color temperatures.