* the predefined luminous efficacy values are typical / average values.
The illuminance Ev in lux (lx) is equal to 10.76391 times the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W) divided by the surface area A in square feet (ft2):
Ev(lx) = 10.76391 × P(W) × η(lm/W) / A(ft2)
The illuminance Ev in lux (lx) is equal to the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W) divided by the surface area A in square meters (m2):
Ev(lx) = P(W) × η(lm/W) / A(m2)