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Business: Transportation


High-Bay Lighting


Until recently, high-intensity discharge (HID) lighting systems were considered the only option for illuminating high-bay spaces. Recent advances in fluorescent lighting systems now make these lower-cost systems more attractive choices for lighting spaces that have high ceilings.

Recently developed fluorescent T5 HO (high output) systems offer a number of benefits. These include:

  • higher light output per unit of electric power
  • higher light output as lamps age
  • better colour rendering
  • energy-saving switching capability
  • continued reliability when there is lamp failure (high-bay fluorescent systems usually have between four and six lamps per luminaire versus one for HID systems; fluorescent systems continue to provide illumination if a single lamp fails)
  • less mercury for equivalent lighting service-years
  • superior performance at higher temperatures

six-lamp T5 HO fluorescent high-bay luminaire

Figure 1 - A six-lamp T5 HO fluorescent high-bay luminaire

The purchase-price premium for high-bay fluorescent systems has been dropping, and operating costs are low enough to make fluorescents worth considering when you must replace HID systems.

How Does Fluorescent High-Bay Lighting Save You Money?

Fluorescent high-bay lighting with T5 HO lamps saves money in a number of ways:

  • Lamp light output is increased – Compared with HID systems, at an operating temperature of 25°C, T5 HO fluorescent systems produce about 30 percent more light per unit of electrical energy. At 35°C, the light output of a T5 HO (linear) improves by about 10 percent.

  • Lamp light output is maintained – Because the light output of lamps declines over service life, the design of the lighting system must be based on the "maintained" or end-of-life light output. The bigger the decline (lumen depreciation), the more excess initial lighting must be provided. T5 HO fluorescent lamps are about 30 percent better than HID lamps in maintaining light output over their service life.

  • Longer lamp life – The rated lamp life of T5 HO (linear) fluorescent lamps is equal to that of 400 W metal halide lamps (20 000 hours) and about 30 percent longer than that of 250 W metal halide lamps. Labour is a significant cost in relamping. Extending the relamping interval saves money.

  • Multiple lamps per luminaire provide redundancy – T5 HO fluorescent high-bay luminaires typically use from four to six lamps each, compared with a single lamp for HID systems. If a single lamp fails, the T5 system continues to provide significant illumination, while the HID system does not. This can allow more flexibility in responding to burnouts.

  • Fluorescent systems switch more quickly – Fluorescent systems require only a couple of seconds to approach full light output; HID systems take from five to ten minutes. Rapid switching allows use of occupancy detectors in rack areas, so that some or all of the lamps may be switched off when a rack aisle is unoccupied.

  • No work time is lost due to momentary power interruptions – Because fluorescent high-bay lights turn on instantly after a momentary power outage, no work time is lost. Even a one-second power outage with HID lighting, however, can mean five to ten minutes of downtime as workers wait for the lights to come back on.

  • Fluorescents have a better colour-rendering index – In colour-critical operations (such as work with colour-coded components and products), errors are reduced and visual tasks are easier to perform.

Although T5 HO luminaires may still be generally more expensive than HID luminaires, the price difference is expected to decline as the technology matures. The compact size of T5 luminaires makes them a "drop-in" replacement for HID luminaires.

Safety and Environmental Considerations

Mercury vapour and the metal halides used in most high-bay lighting are toxic.

Fluorescent lamps use much less mercury than metal halide HID lamps for the equivalent lighting service-years. Facilities should recycle all mercury-containing products, including all HID lamps and T5s.

Next: How Much Will I Save?