Fluorescent High Bays
Be Careful of One Size Fits All Fluorescent High Bays
By John Temple
So you’ve decided to take advantage of the savings opportunities available from fluorescent high bays. Now you are faced with a decision; what fixture and lamp combination is the best for your application.
When it comes to fluorescent high bays, one size definitely does not fit all. There are a number of questions that should be answered before deciding which fixture and lamp combination will work best for you.
What is the space used for?
Are you lighting a warehouse, a manufacturing area, or food processing area? If it’s a warehouse, a linear fixture rather than a 2’x 4’ fixture may provide better vertical illumination, making product selection easier. If it’s a food processing plant, you may be required to use enclosed fixtures. If it’s a manufacturing area, does the equipment generate high heat levels?
Which lamp type is best?
Fluorescent lamps and ballast are more temperature sensitive than High Intensity Discharge (HID) lighting, such as metal halide or high pressure sodium. The two most popular fluorescent high bay lamps are the F32T8 and the F54T5HO. Both lamps are roughly equivalent in their lumens to watt ratios. However, they differ in that T8 fixtures are less expensive than the T5 alternative primarily because the lamps and ballasts are less expensive. There is another significant difference in their ability to cope with high temperatures.
Heat may be a problem
The T8 lamp achieves maximum performance at the temperature used to test and rate most fluorescent lamps, which is 25ºC or 77ºF. The T8 lamp was designed for the typical air-conditioned office environment. The T5HO lamp which was designed for higher heat environments is tested at 35ºC or 95ºF. The lumen output of both lamps will steadily decline as the temperature gets further away from their peak. Although in the case of the T5HO its peak light output is achieved at a temperature that is 23% higher than the T8 lamp.
So what does this mean? It means that if your application is air-conditioned or even refrigerated, either fluorescent lamp is an option. If there is a constant ambient temperature, a fixture can be designed to compensate and potentially even take advantage of the constant temperature. In a refrigerated space designers can use the heat generated by the lamp and ballast to maintain optimum lamp and ballast temperatures, thereby maximizing ballast life and lamp lumen output. In such cases T8’s with their lower lamp and ballast cost may be a
better choice than T5HO. However, if the space is not air-conditioned or refrigerated, the T5HO lamp will be a better choice due to high summer temperatures.
