Luminous intensity measures the power of light emitted in a particular direction, weighted by human eye sensitivity. The candela is the SI base unit.
What Is Luminous Intensity?
The candela (cd) is one of the seven SI base units. It measures light power per solid angle, weighted by the human eye's sensitivity (peaking at 555 nm green light). 1 cd ≈ the light from one candle.
Units and Conversions
- 1 cd = 1,000 mcd
- 1 mcd = 1,000 µcd
A standard LED: 50–500 mcd. A candle: ~1 cd. A 100 W incandescent bulb: ~120 cd (in all directions).
Related Photometric Units
Lumen (lm) = total light output. 1 lm = 1 cd × 1 steradian. Lux (lx) = light falling on a surface. 1 lx = 1 lm/m². These three units together describe the complete picture of light: source intensity, total output, and surface illumination.
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