VISUALLY EFFECTIVE LIGHT

The S/P ratio determines the apparent visual brightness of a light source and determines how much light a lamp produces which is useful to the human eye (i.e. Visually Effective Lumens/Lux).

The S/P ratio of a light source is determined by measuring the output in Lumens or Lux using a light meter or spectrometer calibrated first to the Photopic vision sensitivity curve, and then measuring the same light with instruments calibrated to the Scotopic vision sensitivity curve. The resulting numbers form a ratio that is expressed as a single number.
                                            S/P RATIO
Sun + Sky:                                  2.47
6500k RealTime Induction Lamp:      2.25
5000k RealTime Induction Lamp:      1.96
4100k RealTime Induction Lamp:      1.62
Metal Halide (Na/Sc):                     1.49
High Pressure Sodium(50w):            1.14
Incandescent (2850k):                   1.41                         
Warm White Fluorescent:                1.00
                        (Credit:  Francis Rubenstein of Berkley Labs)
 
S/P Ratio In Action:
50% energy reduction:

    400W Metal Halide lamp [M 400] X 54.6 Lumens/W8 = 21,840 Lumens X 1.497
        = 32,541 useful  lumens

    200W RealTime Induction lamp X 81 Lumens/W = 16,200 Lumens X 1.96 
       = 31,752 useful lumens (50% less energy & the difference is imperceptible to the human eye)

CONCLUSIONS:

1.  RealTime Induction lamps always appear much brighter to the eye than most other light sources, even when those light sources have higher wattages, because the induction lamps produce more light that is useful to the human eye.

2.  You can Replace traditional lighting (i.e. Metal Halide, HPS, Fluorescent, Mercury Vapor etc) w/induction lamp that is half the wattage of a traditional lamp.  That represents 50% reduction in power consumption.