Luminous intensity is an important value for comparing different lamps. Lamps with the same luminous flux can have completely different luminous intensities due to their beam angle. The beam angle indicates the angle at which the light is emitted by the lamp.
The luminous intensity or its candela value indicates how intensively the light is emitted. The more focused the light is emitted, the more intense it is. The diagram shows two lamps with the same luminous flux (lumen) but different beam angles. The luminous intensity of the lamp with the smaller beam angle is higher than that of the lamp with the wider beam angle.
How to measure light intensity?
To determine the luminous intensity of a lamp, you need the luminous flux and the beam angle or solid angle. The value of the luminous- or light intensity is given in candela. The units of luminous flux are lumens, for the solid angle it is steradians.
Luminous intensity [cd] = luminous flux [lm] / solid angle [sr].
If the solid angle is not known, but only the beam angle, this can be determined with a conversion formula:
If the calculation according to the above formulae is not possible for the lamp, a light measurement can be carried out with an integrating sphere and a spectrometer. This creates a luminous intensity distribution curve. From this, conclusions can be drawn about the luminous intensity.
A standard candle, for example, emits a luminous intensity of 1 cd, i.e., it emits about 12 lumens (lm) in all directions.
Post time: Aug-10-2022