Which unit is used to describe light intensity in this context?

• A. Lux
• B. Foot-candles
• C. Lumens
• D. Candela

Answer: (B)

Light intensity in this context refers to how bright a surface is illuminated by a light source. That brightness on the surface is called illuminance, which measures how much luminous flux reaches a defined area. Foot-candles express illuminance as lumens per square foot, so they directly describe how bright a workspace or animal-housing area will appear. This makes foot-candles the most appropriate unit for describing surface lighting levels in practical lab settings. By contrast, lumens measure the total light emitted by the source, candela describes the light’s intensity in a specific direction from the source, and lux (the SI equivalent) measures illuminance per square meter. Since the context uses a square-foot area to describe lighting, foot-candles fit best. A handy conversion is that 1 foot-candle equals about 10.764 lux.