Here’s an explanation of how the standard dictates we specify peak beam intensity and beam distance. This is industry standard and set out in ANSI/NEMA FL-1 Standard
Peak Beam Intensity (Candela)
Peak beam intensity is a measurement of luminous intensity at the most intense portion of the beam. Peak beam intensity is measured using a lux meter, taking the highest lux reading at the most focused section of the beam. The lux reading is then multiplied by the squared value of test distance in meter to convert lux to candela. Example: 2,000 lux measured from 2 meters away would yield a result of (2,000 Lux) * (2 meters)2 = 4,000 Candela
Beam Distance (Meter)
Beam distance is the theoretical distance from the light source at which the illuminance is equal to a full moon on a clear night (0.25 lux). This is a calculated distance and is calculated using the peak beam intensity value. As peak beam intensity rises, beam distance rises. As peak beam intensity falls, beam distance falls. The relationship is not linear, as the equation is