What is Candela (cd)

The candela (symbol: cd) is the SI base unit of luminous intensity. It represents the power emitted by a light source in a specific direction, taking into account the luminosity function. For example, a typical candle emits light with a luminous intensity of approximately 1 cd.

Candela refers to the amount of light emitted by a fixture in a specific direction, while lux measures the level of light that illuminates a surface.

1 candela is equivalent to 12.57 lumens. However, it is not advisable to directly compare the values of lumens and candela when it comes to lighting devices.

The calculation can be done using the formula 1lm = 1cd * 1. This means that 1 lumen is equal to 1 candela. In other words, a light source with an intensity of 1 candela will produce 1 lumen of luminous flux in a sphere with a surface area of 1 square meter.

The luminous intensity of a 100 watt unidirectional bulb is equivalent to 100 candela.

In 1979, the General Conference on Weights and Measures (CGPM) established a new definition for the candela (cd). It is now defined as the luminous intensity, in a specific direction, of a source that emits monochromatic radiation with a frequency of 540 × 10^12 hertz. Additionally, the radiant intensity of this source in that direction is equivalent to 1/683 watt per steradian.

For a more up-to-date comparison, a standard incandescent lightbulb typically produces around one candela per watt.

A higher candela rating indicates that the light emitted is more intense, allowing it to travel a longer distance. Torches with high candela ratings are ideal for situations where visibility is reduced, such as in smoke or fog, and when a concentrated beam is desired.