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 lumenper 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: