Question 1

What is light intensity and how is it measured?

Accepted Answer

Light intensity can mean luminous intensity (candela), illuminance (lux/foot-candles on a surface), or irradiance (W/m² power). Context determines which measurement applies.

Question 2

How does distance affect light intensity?

Accepted Answer

Light follows the inverse square law: intensity decreases with distance squared. Double the distance = 1/4 the light. This is why flash photography has limited range.

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.

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