At many facilities, when a lamp burns out, all the following steps are taken as part of spot relamping. A technician determines the lamp type, possibly by a visit to the site, gets a lamp, carries a ladder to the site, opens the fixture, replaces the lamps and then arranges for disposal.
The entire process may well distract employees near the lamp. And without close oversight, the last step is often truncated by simply dropping the lamps into the nearest dumpster where they are quickly covered — and probably smashed — by other trash, releasing their mercury. The labor involved in this process may be a significant hidden cost, especially when compared to alternatives.
Most lamp manufacturers and lighting maintenance firms recommend changing lamps before they burn out, with good reason. While perhaps a bit counterintuitive, doing so greatly reduces labor wasted on spot relamping, reduces workplace disruption and better controls lamp disposal. Lamps are replaced en masse (usually during off hours) as they approach about 60 to 70 percent of their rated lives, which is when roughly 10 percent may have burned out and before failure rates begin to climb.
For some types of high intensity discharge (HID) lamps, significant color change may occur prior to burnout. If color or color rendering are important, early replacement may also help maintain lighting quality.
Such group relamping is often done by crews whose main focus and experience is time-efficient fixture maintenance because they are paid on a piece rate basis. Trained in proper lamp disposal, they take responsibility for off-siting and documenting removed lamps.
Group relamping that follows a written work specification will also ensure the following worthwhile tasks are performed:
While lamp lives vary, group relamping cycles for linear fluorescent lamps are often spaced about four to five years apart. That calculation is based on a typical 20,000-hour-lamp lifetime which is when (by definition) 50 percent of lamps will have burned out. At 70 percent of that time, for example, and 3,000 annual burn hours, a cycle of 4.7 years can be derived. Group relamping may be sequenced floor-by-floor, or done for an entire building, as desired to accommodate operations, crew size, etc. Lamps are gathered and disposed of in large groups, simplifying compliance with environmental regulations — which, for mercury, are becoming tighter. Since lifetimes for HID and compact fluorescent lamps (CFLs) differ from linear fluorescents, adjustments in that calculation are necessary.
In the past, replacing lamps prior to burnout was also recommended to avoid the normal drop in light levels due to lumen depreciation as lamp output diminished and dirt depreciation as fixture and lamp surfaces degraded. While that’s still valid, several changes have occurred in the last decade that may affect group relamping cycles and costs:
Studies by the International Association of Lighting Maintenance Companies (NALMCo) during the last decade found that, in non-industrial spaces, a lower dirt depreciation factor could be used in designing or upgrading lighting systems. In carefully controlled tests performed over many months, NALMCo determined light losses due to dirt. As seen in the box on this page, prior dirt depreciation curves for lensed and louvered fluorescent fixtures involved light losses of about 22 percent and 30 percent by the time a group relamping would be performed. (See bottom two curves in box.)
Ensuring acceptable light levels between fixture cleanings then meant installing additional fixtures, raising installation costs and boosting energy costs. New findings (see the top curve in box) for both types of fixtures indicate loss levels of about 12 percent, thus opening the door to less frequent cleaning or switching to low-power lamps or ballasts in existing fixtures.
While the fact that fixtures are staying cleaner is not a good reason to avoid cleaning them, it may indicate that fixture washing — often a task included in group relamping — may not be needed as often. Some maintenance firms instead perform a simple wipe down of fixture reflectors using an anti-static cloth when changing lamps.
In the past, one of the major reasons for early relamping was that fluorescent lamp lumen output dropped significantly over time — more than 20 percent by 70 percent of rated life for T12s. Because such a drop in output could affect productivity, sales and safety (each of which is worth a lot more than lamps), it always makes sense to maintain light levels.
Some new lamp types (e.g., T5s, some T8s, better CFLs), however, now hold their output much higher (losing about 10 percent or less of their output at 70 percent rated life). Some premium versions boast even better lumen maintenance and exceptionally long life (e.g., 30,000 instead of 20,000 hours). Some of these factors may also reduce the demand for occasional spot relamping in critical areas (e.g., executive offices, medical spaces). As a result, facility executives may wish to weigh the option of improving their lamp purchasing specs as part of their lighting maintenance efforts.
When considering a group relamping contract or internal project, a facility’s mix of lamp types and their characteristics are important parameters for calculating the right relamping cycle period. Many lighting maintenance contractors will, in their proposals, provide an economic analysis to compare existing spot relamping efforts with group relamping in order to show dollar savings on labor and disposal. When making such comparisons, it pays to look closely at the numbers. Here are a few tips that may yield more realistic results.
To find a qualified lighting maintenance contractor, look for firms that are members of NALMCo. Such firms seek to maintain a higher level of service and typically have personnel holding NALMCo’s Certified Lighting Maintenance Contractor (CLMC) standing.
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Changing View of Luminaire Dirt Depreciation (LDD)
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Lindsay Audin is president of EnergyWiz, an energy consulting firm based in Croton, N.Y. He is a contributing editor for Building Operating Management.
Cleaner fixtures in non-industrial spaces have significantly reduced luminaire dirt depreciation — light losses due to dirt on fixtures. As a result, it may be possible to clean existing fixtures less often or to switch to low-power lamps or ballasts. (Reprinted from IESNA RP-36-03 with permission from the Illuminating Engineering Society of North America.)
