III. Declared Useful Luminous Flux (φ)
The declared luminous flux is more complex to find, and relates directly to the construction of the light source and how its flux is directed. This value states a range in the quantity of emitted light intensity according to a given volume, and an appropriate laboratory measurement is necessary to determine it.
IV. Efficacy Factor (F)
The efficacy factor of a light source is a simple coefficient that is assigned based on the directionality of the light source:
- F = 1.00 for non-directional light sources (NDLS, using total luminous flux)
- F = 0.85 for directional light sources (DLS, using the flux in a cone whose vertex is located at the light source)
V. Color Rendering Index (CRI)
The color rendering index represents the ability of a light source to realistically render the colors of the visible spectrum when it reflects on an object. Some precise calculations are necessary to have the exact figure, although an approximation according to the type of light is also possible: