International Dark-Sky Association (IDA)

3545 N. Stewart Ave., Tucson AZ 85716 U.S.A.

E-mail: crawford@darksky.org

WWW: http://www.darksky.org

Operating Data and the Economics of Different Lamps

Information Sheet 4, January 1990

Assume:

4100 hours of use per year (average nighttime hours, dusk to dawn)
8¢ as the cost per KWH (Kilowatt hour, the power rate)

Low Pressure Sodium

                             180W    135W     90W     55W     35W     18W
                          -----------------------------------------------
Initial Lumens              33000   22500   13500    8000    4800    1800 
Mean Lumens                 33000   22500   13500    8000    4800    1800
Lamp Wattage                  180     135      90      55      35      18
Circuit Wattage               220     180     125      80      60      30
Intial Lum/watt               150     125     108     100      80      60
Mean Lum/watt                 150     125     108     100      80      60
Annual KWH Use                902     738     513     328     246     123
Annual Oper Cost           $72.16  $59.04  $41.00  $26.24  $19.68   $9.84

High Pressure Sodium

                     400W    250W    200W    150W    100W     70W     50W
                   ------------------------------------------------------
Initial Lumens      50000   27500   22000   16000    9500    6000    4000
Mean Lumens         45000   24750   19800   14400    8550    5500    3600
Lamp Wattage          400     250     200     150     100      70      50
Circuit Wattage       465     294     246     193     130     100      66
Intial Lum/watt       108      94      89      83      73      60      61
Mean Lum/watt          97      84      80      75      66      55      55
Annual KWH Use       1907    1205    1009     791     533     410     271
Annual Oper Cost  $152.52  $96.43  $80.69  $63.30  $42.64  $32.80  $21.65

Mercury Vapor

                    1000W    700W    400W    250W    175W    100W
                   ----------------------------------------------
Initial Lumens      55000   36400   20500   11850    7850    4100 
Mean Lumens         46200   29850   18570   10540    7140    3230
Lamp Wattage         1000     700     400     250     175     100
Circuit Wattage      1090     765     455     285     205     135
Intial Lum/watt        50      48      45      42      38      30
Mean Lum/watt          42      39      41      37      35      24
Annual KWH Use       4469    3137    1866    1169     841     554
Annual Oper Cost  $357.52 $250.92 $149.24  $93.48  $67.24  $44.28

Metal Halide

                                                         Incandescent
                    1000W    400W    250W    175W |  300W    200W    150W
                   -------------------------------|----------------------
Initial Lumens     110000   34000   19500   14000 |  6360    4000    2880
Mean Lumens         88000   25600   17000   10800 |  6360    4000    2880
Lamp Wattage         1000     400     250     175 |   300     200     150
Circuit Wattage      1140     465     295     220 |   300     200     150
Intial Lum/watt        96      73      66      64 |    21      20      19
Mean Lum/watt          77      55      58      49 |    21      20      19
Annual KWH Use       4674    1907    1210     902 |  1230     820     615
Annual Oper Cost  $373.92 $152.52  $96.76  $72.16 |$98.40  $65.60  $49.20

Most columns are lined up at nearly equal lumen output, to show the relative energy & cost savings.

This material is copyrighted (©) by the IDA, or others as noted. It may be reproduced for non-commercial usage provided that credit is given to IDA. Provided here by NELPAG via permission by IDA, to aid in the availability of this important information.

A key source for information on outdoor night lighting is the International Dark-Sky Association (IDA).