Definition
Candela (symbol: cd) is the SI base unit of luminous intensity — the amount of light emitted by a source in a particular direction per unit solid angle. One candela is approximately the light output of a single candle (hence the name). Unlike lumens (total light output in all directions) and lux (light falling on a surface), candela measures directional intensity — critical for spotlights, track lights, floodlights, and any application where beam direction and peak intensity matter. In lighting design, candela values from IES photometric files drive all illuminance (lux) calculations in software like DIALux and AGi32. The relationship: 1 cd = 1 lm/sr (lumen per steradian of solid angle).
Key Data
| Parameter | Value / Explanation |
|---|---|
| Typical candle flame | ~1 cd (the historical reference point for the unit) |
| LED MR16 spotlight (25°) | 1,000-3,000 cd center beam |
| LED track spot (15° narrow) | 5,000-15,000 cd — tight beam, high center intensity |
| LED floodlight (wide 60°) | 2,000-8,000 cd — spread intensity over wider area |
| Airport runway light | 20,000-50,000 cd — extreme directional intensity for visibility at distance |
| Center Beam Candlepower (CBCP) | Industry term — candela measured at the center (maximum intensity point) of the beam |
Application Guide
Jewelry display spotlight
5,000-8,000 cd, 10-15° beam, CRI 95+
High center intensity makes diamonds sparkle; tight beam focuses attention
Cathedral / high ceiling
15,000-25,000 cd, 8-12° beam, high-power LED
Extreme mounting height requires high candela to deliver adequate lux at floor level
Outdoor area flood
3,000-8,000 cd, 60-120° beam, wide distribution
Spread light across large area; candela traded for coverage
Conclusion & Procurement Recommendation
For B2B procurement of directional luminaires: always request the IES photometric file showing the complete candela distribution table (Type C photometry: 0-180° vertical, 0-360° horizontal). The candela table enables accurate illuminance calculations in lighting design software. Key specifications: (1) Center Beam Candlepower (CBCP) — peak intensity at beam center, (2) Beam angle — angle where intensity drops to 50% of CBCP, (3) Field angle — angle where intensity drops to 10% of CBCP. For accent/display lighting, specify CBCP and beam angle rather than lumens — two 1,000-lumen spotlights can have vastly different visual impact depending on beam concentration.