Formulas for determining Group Relamping and Spot Relamping Costs

There are a variety of reasons to practice group relamping, in which a set of lamps is replaced at a scheduled time, rather than spot relamping, in which lamps are only replaced when they burn out. Most of these reasons apply to fluorescent and high-intensity discharge (HID) lamps rather than incandescents, which have much shorter lifetimes.
• Group relamping requires much less labor per lamp than spot relamping. A worker might take as long as a half hour to retrieve and install a single lamp. If all the materials were on hand for a large number of lamps, a worker could move systematically from fixture to fixture and cut the required time to about 3 minutes per lamp. The process would also be less disruptive, because group relamping is usually done outside working hours.
• Group relamping is easy to schedule and delegate to outside contractors, who have special equipment and training.
• Group relamping provides brighter and more uniform lighting because lamps are replaced before their output has fully depreciated. Direct energy benefits result if the designer, anticipating group relamping, uses a smaller safety factor.
• Group relamping offers increased control over the replacement lamps, reducing the chances of mixing incompatible lamps—such as those with different color temperatures.

Group Relamping Cost
Annualized Cost ($) = A x (B + C)
A = Operating Hours/Year ÷ Operating Hours Between Relampings

B = (Percentage of Lamps Failing Before Group Relamping x Number of Lamps) x (Lamp Cost + Labor Cost to Spot Replace 1 Lamp)
C = (Lamp Cost, Group Relamping + Labor Cost to Group Relamp 1 Lamp) x Number of Lamps



Spot Relamping Cost

Average Annual Cost ($) = (Operating Hours/Year ÷ Rated Lamp Life) x (Lamp Cost + Labor Cost to Replace 1 Lamp) x Total Number of Lamps

GROUP vs. SPOT ANALYSIS

T8 lensed troffers
Group relamping has higher lamp costs but much lower labor costs, in this case providing a 31 percent overall savings. Group relamping also provides additional benefits in lighting quality and easier facility management.
Relamp cycle (hours) Average relamps per year Average material cost per year Average labor cost per year Total average cost per year
Spot relamping on burnouta 20,000 525 $1,391 $3,150 $4,541
Group relamping at 70% of rated life)b 14,000 750 $1,988 $1,125 $3,133
——————— —————— ——————— —————
Difference 225 $597 -$2,025 -$1,428
(31% savings)

Notes:
a. Assumes labor costs of $6.00/lamp for relamping and cleaning, material cost of $2.65/lamp, and 3,500 hours/y operation.
b. Assumes labor costs of $1.50/lamp for relamping and cleaning, same material costs and operating hours as for spot relamping.
Source: U.S. Environmental Protection Agency