How to Calculate Luminous Intensity

What is Luminous Intensity?

Luminous flux (lumens) is the total perceived light output. Luminous efficacy (lm/W) measures how efficiently electricity is converted to visible light. LED: 80–120+ lm/W vs incandescent: ~15 lm/W.

Formula

Luminous flux (lumens) = Luminous intensity (candelas) × Solid angle (steradians) | 1 lumen ≈ 1 candela × 1 steradian

Step-by-Step Guide

1Lumens = Watts × Efficacy (lm/W)
2Higher lumens = brighter light
3Higher lm/W = more efficient; lower running cost
4800 lumens ≈ old 60W incandescent brightness

Worked Examples

Input

10W LED, 100 lm/W efficacy

Result

1,000 lumens — equivalent to ~75W incandescent

Frequently Asked Questions

What is Luminous Flux?

Luminous flux (lumens) is the total perceived light output. Luminous efficacy (lm/W) measures how efficiently electricity is converted to visible light

How accurate is the Luminous Flux calculator?

The calculator uses the standard published formula for luminous flux. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Luminous Flux calculator use?

This calculator works with inches, watts. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Luminous Flux calculator use?

The core formula is: Lumens = Watts × Efficacy (lm/W). Each step in the calculation is shown so you can verify the result manually.

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