Intensity is the brightness of light. The unit of measurement of light intensity
in the English system is the foot-candle (fc), which is one lumen per square
foot (lm/ft2
). In the SI system the unit is the lux (lx) which is one lumen per
square meter (lm/m2
). The phot (ph) is also used and is defined as one lumen
per square centimeter (lm/cm2
). The lumen replaces the candela (cd) in the SI
system. The dB is also used for the comparison of light intensity as follows: