Luminous Flux Calculator

Luminous flux is the total amount of light a source emits — a key spec for comparing bulbs, LEDs, and lighting fixtures. Enter a light source's luminous intensity (in candela) and beam angle into the Luminous Flux Calculator, then select your calculation type — intensity to flux or flux to intensity — to get the luminous flux in lumens. Secondary outputs include the calculated luminous intensity in candela and the solid angle in steradians.

cd

Light intensity in candela (cd) - usually found in LED datasheets

°

Full beam angle in degrees

lm

Input flux when calculating intensity from flux

Results

Luminous Flux

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Luminous Intensity

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Solid Angle

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Frequently Asked Questions

What is the difference between luminous flux and luminous intensity?

Luminous flux (lumens) measures the total light output from a source, while luminous intensity (candela) measures how bright the beam appears in a specific direction. Flux considers the entire light emission, intensity focuses on directional brightness.

How do I find the luminous intensity of an LED?

LED luminous intensity is typically listed in the product datasheet or specifications, usually measured in millicandela (mcd) or candela (cd). Look for values like 'luminous intensity at peak wavelength' or 'axial luminous intensity'.

Why does beam angle affect luminous flux calculation?

Beam angle determines how the light is distributed. A narrow beam concentrates light in a smaller solid angle, while a wide beam spreads it over a larger area. The solid angle (calculated from beam angle) is essential for converting between intensity and total flux.

What beam angle should I use for different applications?

Narrow beams (15-30°) are ideal for spotlights and accent lighting. Medium beams (30-60°) work well for task lighting. Wide beams (60-120°) are perfect for general ambient lighting and area illumination.

How accurate is this luminous flux calculation?

This calculator assumes a uniform light distribution within the beam angle, which is accurate for most LEDs and standard light sources. For complex beam patterns or non-uniform distributions, professional photometric testing may be needed.

Can I use this calculator for any type of light source?

Yes, this calculator works for any light source where you know the luminous intensity and beam angle - including LEDs, halogen bulbs, fluorescent lights, and other fixtures with defined beam characteristics.