History of High Bay Fixtures and Recent Technology Changes

High-intensity discharge (HID) light sources, such as metal halide and high-pressure sodium fixtures, have long dominated the market for lighting indoor spaces with high ceilings. These "high-bay" spaces are typically found in warehouses, factories, large retail stores, and athletic facilities.

In recent years, technology changes, general improvements in fluorescent lamps and the emergence of high-intensity fluorescent high bay fixtures have made fluorescent lighting the most cost-effective choice for lighting high ceiling indoor spaces. These high-intensity fluorescent high bay systems are more energy-efficient than HID solutions and feature lower lumen depreciation rates, better dimming options, virtually instant start-up and re-strike, better color rendition, reduced glare, better “pupil lumens” (fluorescents produce a much greater amount of light within the visible spectrum of the human eye than the HID) and lower energy consumption.

HID fixtures produce intense light in such a small area that they are considered "point sources." The T8 high bay fixtures use highly reflective aluminum specular reflectors (specular reflection is the mirror-like reflection of light from a surface, in which light from a single incoming direction (a ray) is reflected into a single outgoing direction), to direct the light emitted from the lamps in a much wider array than an HID fixture. The result is an overlapping of light emitted by neighboring fluorescent high bay fixtures that produces a very uniform light in a work area. HID fixtures, which are point source lights, produce very bright light in spots but have very poor light uniformity between the fixtures.

The T8 fluorescent high bay fixture can generate large amounts of light and is excellent for lower to mid hanging heights. This fluorescent high bay fixture type is available in many configurations including 2-lamp, 4-lamp, 6-lamp, 8-lamp, 10-lamp, 12-lamp and 16-lamp fixtures. The advantage the T8 high bay has over the T5 model is the T8 fixture consumes less energy than the T5 fluorescent high bay fixture. A typical 6-lamp, T8 high bay consumes approximately 218 input watts (using two 3-lamp High Ballast Factor electronic ballasts per fixture at 277 volts) and the 6-lamp T5 high output fixture consumes approximately 351 input watts (using one 4-lamp and one 2-lamp electronic ballast per fixture at 277 volts). This equates to energy savings of almost 38 percent using the T8 model. Of course, the 6-lamp T8 high bay fixture will only produce approximately 18,000 lumens (6 X 3,000 lumens) as compared to a 6-lamp, T5 high bay fixture which will produce approximately 30,000 lumens (6 X 5,000 lumens).