What is the approximate luminous intensity of unfocused lights used as visibility aids?

• A. 25 candelas.
• B. 100 candelas.
• C. 1 candela.
• D. 0.5 candela.

Answer: (A)

Unfocused visibility lights spread light over a wide angle to be seen rather than to signal a precise point. Because they’re not concentrated into a beam, a moderate luminous intensity is used so they’re detectable at typical operating distances without being glaring. About 25 candelas provides enough brightness to be noticed while avoiding excessive glare or misinterpretation that a brighter beacon could cause. Lights around 0.5 to 1 candela would be too dim to see reliably in real conditions, and something as bright as 100 candelas would be unnecessarily intense for a general visibility aid.