to the United States 
Lumens and candelas measure different aspects of light, making direct conversion between the two units complex and dependent on specific conditions.
- Lumens (lm) measure the total amount of light emitted by a source in all directions. It’s a measure of the total “flow” of light.
- Candelas (cd) measure the intensity of light in a specific direction. It’s defined as lumens per steradian (a unit of solid angle).
The relationship between lumens and candelas depends on the beam angle of the light source:
- For an isotropic light source (one that emits light equally in all directions).
1 candela = 4π lumens (approximately 12.57 lumens) - For a light source with a specific beam angle.
Candela = Lumens / (2π * (1 – cos(beam angle / 2)))
However, for most real-world light sources, especially those with complex beam patterns, a simple conversion is not possible without detailed information about the light distribution.
In practice:
- Lumens are typically used to describe the total light output of a source.
- Candelas are often used in applications where the directionality of light is important, such as in spotlights or headlights.
When working with lighting, it’s often necessary to consider both measurements to fully understand a light source’s characteristics. If you need to convert between the two, you’ll typically need additional information about the light distribution pattern of your specific source.
