Design Lumens vs. Pupil Lumens & Usable Light

In lighting design there are two distinct kinds of lumen output produced by lamps. The first is called photopic or design lumens, which represent the relative sensitivity of the eye under intense lighting such as full outdoor sun. Photopic lumen output is the amount of light registered by the cones in the human eye and is measured by standard lumen and footcandle meters.

The second type of lumens are called scotopic, which represent the sensitivity of the eye under typical interior lighting conditions and cannot be measured directly with a standard light meter. Scotopic lumen output is the amount of light registered by the rods of the human eye and also controls pupil size directly effecting visual acuity for tasks.

For lighting interior spaces a correction factor may be applied to photopic lumen readings to find the usable light produced by a given light source, also called pupil lumens. As shown below, two different light sources having similar design lumen readings taken by a standard light meter can have drastically different usable light outputs and apparent brightness.


4000k MVR Metal Halide
85 Design Lumens/Watt
107 Pupil Lumens/Watt

UltraLux™ High Bay w/BlueMax™
98 Design Lumens/Watt
196 Pupil Lumens/Watt
Design Lumens vs. Pupil Lumens/Usable Light Source:
Platts Research & Consulting
Light Source
Design Lumens/Watt
Correction Factor
Pupil Lumens/Watt
BlueMax™ T5 Fluorescent
98
2.0
196
4100k T5 Fluorescent
90
1.62
145
Clear Metal Halide
85
1.49
126
5000k Triphosphor Fluorescent
70
1.58
111
4000k Multi-Vapor Metal Halide
85
1.26
107
6500k Daylight Fluorescent
55
1.72
95
3500k Triphosphor Fluorescent
69
1.24
85
Vitalite Fluorescent
46
1.71
79
5000k 90 CRI Fluorescent
46
1.70
78
2900k Warm White Fluorescent
65
0.98
64
Low-Pressure Sodium
165
0.38
63
50watt High-Pressure Sodium
65
0.76
49
Deluxe Mercury Vapor
40
0.86
34
35watt High-Pressure Sodium
55
0.57
31
Tungsten Halogen
22
1.32
29
Standard Incandescent
15
1.26
19