When all of the lamps in a system are replaced at one time
after a fixed interval, it is referred to as group relamping.
The fixed interval is called the economic group relamping interval.
Benefits of group relamping are reducing the cost in the operations
of the lighting system and improving illluminance. In considering
the redesign of a lighting system, if group relamping is deemed
to be economical, less over design will need to be considered.
This will lead toward a savings in the initial cost of the design
and the operating and maintenance costs associated with the
new system.
Group relamping savings are the result of labor cost savings.
The cost to replace one lamp one at a time as they fail is usually
less. However, it makes more sense to replace all the lamps
if the labor savings exceed the value of the used lamps even
though there is still life left in some of the lamps.
Group relamping should be considered if:
The labor cost of spot-replacing one lamp less
the cost of group replacing one lamp exceeds the cost
of one new lamp.
There are analysis techniques available to aid in determining
the economic group relamping interval. These include the mortality
rates of the lamp, labor rates, and cost and depreciation rate
of the lamp. At 70% to 80% of the rated life it has been found
to be the most economical time to group relamp. This also is
at the time when the cost per lumen becomes uneconomical to
continue operating the lamps. The cost of replacing spot failures
should also be taken into account in making the final calculation
so that optimum appearance and quality of light are kept.
Thus scheduled intervals of maintenance of the lighting system
can be expanded to include installing other component parts
for optimizing the system and providing energy efficient replacements.
Additional information may be found in
the IESNA Lighting Handbook.
