In your school or facility, how often does one burned out light bulb that cost a few dollars require maintenance personnel to grab a ladder and spend 20 to 30 minutes to get the job done and return to other work?
The lighting engineer types call this approach to replacing a bulb “spot relamping.”
The alternative approach works like this. Replace all the light bulbs in a given area at a scheduled time. Do the work off-peak hours and use the time to fix faulty sockets, replace old ballasts and even clean fixture lenses. This is called “group relamping.”
The primary advantage to group relamping is that it saves money. Facilities who have implemented it say the costs are up to five times lower compared to spot relamping. Efficient utilization of labor overwhelms the added cost of replacing bulbs that still have some life left.
Why Group Relamping Instead of Spot?
The logic of group relamping is reinforced by inevitable bulb lumen depreciation, the decrease in light output of a bulb until it goes dark. For example, take a T8 fluorescent bulb with an initial lumen rating of 3,000 lumens and a rated bulb life of 24,000 hours. At 40% of rated life (9600 hours) the lumen output has fallen to 2,800 lumens, roughly 7% depreciation. Mean lumens are often calculated at 40% of rated bulb life. From this point on in the life of the bulb, light output continues to decline.
Advocates of group relamping often target 70% of rated life for replacing all the bulbs. At this point, the bulb still operates but the light levels have dropped enough so that if a new bulb was installed next to the 70% bulb, the human eye could see the difference in brightness. The key is to look at the average rated life and expected lumen depreciation of bulbs in various areas of the building. Then, formulate group relamping schedules specific to the bulb type.
Benefits of Group Relamping
Group relamping benefits apply equally to metal halide installations in big box retail and warehouses. These light bulbs are usually installed in high bay ceiling fixtures that require special lifts to reach. The labor time to replace one bulb can be significant.
Light output for most metal halide bulbs decreases to around 60% of initial at roughly half of rated life. Noticeable lamp color shift also happens by this time. Venture Lighting, a manufacturer of HID lamps, uses a chart to demonstrate the lumen maintenance benefits of group relamping. The chart shows an almost 20% increase in average lumen output with a well planned group relamping schedule compared to spot relamping.
Of course, even with any group relamping program in place, a small percentage of light bulbs will break or fail early in life and must be replaced. Calculations comparing group and spot relamping costs (labor plus the cost of bulbs) should take into account the fact that some outlier bulb change costs should be added to the group relamping total.
If you want to get the optimum light output for your energy dollar, and, likely reduce your annual lighting budget, it is worth considering group relamping.
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