The lumen ratings of Low Pressure Sodium lamps are based on the average performance of large groups of lamps operated at rated watts in the specified operating position on a standard reference reactor. Low Pressure Sodium lamps have the highest luminous efficacy of any available light source. In this table, the range of Low Pressure Sodium lamp efficacies is compared to the efficacies of other light sources.
| Lamp Type | Wattage Range |
Initial Efficiency
(Lumens per Watt) |
| Low Pressure Sodium
| 18-180
| up to 200
|
| Fluorescent
| 15-215
| 55-100
|
| Incandescent
| 6-1500
| 4-20
|
| Tungsten Halogen
| 50-1500
| 18-22
|
| High Pressure Sodium
| 35-1000
| 40-140
|
| Metal Halide
| 70-1500
| 80-125
|
| Mercury Vapor
| 40-1000
| 32-63
|
Lumen-per-watt (efficacy) ratings reflect only the watts consumed by the lamp itself and not the total system watts, which include the power consumption of the ballast. The approximate system wattage for each Low Pressure Sodium lamp type appears in this table.
| Nominal Lamp Wattage |
Ballast Loss (%) of Lamp Wattage |
| 35
| 60
|
| 55
| 80
|
| 90
| 125
|
| 135
| 178
|
| 180
| 220
|
