Question 1

What is the difference between candela and lumens?

Accepted Answer

Candela measures luminous intensity (brightness in one direction), while lumens measure total light output in all directions. A focused flashlight has high candela but may have lower lumens than an omnidirectional bulb.

Question 2

How do I convert candela to lumens?

Accepted Answer

Lumens = Candela × Solid Angle (steradians). For a point source: Lumens = Candela × 4π. For a spotlight with beam angle θ: Lumens = Candela × 2π × (1 - cos(θ/2)).

Question 3

What's the difference between lumens and lux?

Accepted Answer

Lumens measure total light output from a source. Lux measures light arriving at a surface. Same lumens in a smaller area = higher lux.

Question 4

How do I convert old wattage to lumens?

Accepted Answer

Roughly: 40W incandescent ≈ 450 lumens, 60W ≈ 800 lumens, 100W ≈ 1600 lumens. LED equivalents use 80-90% less power for same lumens.

cd to lm Converter

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