Assume that 40% of the light emitted by a 1000 W metal halide lamp (110 000 lumens) illuminates a surface with the area of a 32 ft diameter.
a. Determine the average illuminance of the surface in foot-candles.
b. Determine the average illuminance of the surface in lux.
c. What would the average illuminance be if only half of the light illuminated the surface?