Calculate luminous flux (lm) from luminous intensity (cd) and conical apex angle (°)

This calculator allows calculation of luminous flux (lm) from luminous intensity (cd) and conical apex angle (°).

LEDs are often described as having some luminous intensity and a viewing angle. This calculator will extimate the total luminous flux.

The calculator estimates two quantities:

luminous flux within the half power cone (lmH); and

total luminous flux (lmT).

The calculator assumes that the LED has a single beam symmetric around its axis, that flux density (lm/sr) decreases linearly though the apex cone. This should suit most focussed or unfocussed single LED elements, and some symmetric or nearly symmetric arrays, but not rectangular arrays that are significantly asymetric.

The quantity lmT/lmH is the ratio of total luminuous flux to the luminous flux in the half power cone. It defaults to 1.85 which is not a bad guess for lens or mirror focussed LEDs, 1.5 might be a better guess for flat 5630 LEDs.

If power is provided, it also calculates luminous efficiency.

If radius is given, it also calculates luminous flux.

The results can serve as a saneness test on published product claims.

Inputs:



Conical apex angle (°):
Power (W):
Radius (m)
lmT/lmH

Results:
Conical solid angle (sr)
Luminous intensity (cd)
Luminous flux H (lm)
Luminous flux T (lm)
Power (W)
Luminous efficiency (lm/W)
Luminous flux density (lx)

The calculator does not do a lot of error checking, if you enter nonsense, it will probably produce nonsense.

Changes

Version	Date	Description
1.01	14/04/2016	Initial.
1.02	11/10/2023	Added lmT/lmH.
1.03
1.04
1.05

Calculate luminous flux (lm) from luminous intensity (cd) and conical apex angle (°)

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Changes