Consider ambient temperature in lighting decisions
Select the correct fixture for the appropriate environment
While facilities will differ in their lighting requirements, designers should consider several elements when planning a lighting retrofit. One such conideration is ambient temperature.
Heat is a tremendous challenge in many manufacturing facilities and not only degrades the light but can negatively impact the fixtures’ electronic components. Designers should always specify luminaires with a third party listing agency designation, such as Underwriters Laboratory, to insure that it is suitable for the ambient temperature that it will be subjected to.
UL classifications for light fixtures are typically 25ºC (77ºF), 40ºC (104ºF), 55ºC (131ºF) and 65ºC (149ºF). Light fixtures should always have a higher rating than the ambient temperatures at the location that the lighting fixture is mounted. Ambient temperatures at mounting heights often substantially exceed those at floor level.
If for example, the ambient temperature is 35ºC in the area where fixtures will be installed, the luminaires should have 40ºC rating. An installation with a 59ºC ambient temperature should install 65ºC rated fixtures.
A 65ºC ambient rating is the highest fixture rating available. If the ambient temperature exceeds 65ºC, fixture ballasts should be remotely mounted in an area with a lower ambient temperature.
Foundries are an excellent example of an application that will require 55ºC or 65ºC UL rated luminaires. A quality high intensity discharge (HID) system with core and coil ballasts can operate efficiently at these higher temperatures when designed with adequate measures to dissipate heat. Most electronic HID ballasts are also able to tackle 55ºC environments provided the fixtures include adequate heat sinks and conductivity to ensure the fixture keeps the internal temperatures (“case temperatures”) of the ballast below their maximum operating limit as indicated by the ballast manufacturer.
The electronic ballasts in fluorescent systems have similar construction but T5 and T8 lamps are not designed to operate in extremely hot or cold environments. Lumen output is usually substantially diminished within industrial environments where elevated heat is of concern.
For example, a heavy equipment manufacturer wanted to boost light levels to 60 footcandles in an area of the plant that was previously lit with a combination of aged high pressure sodium fixtures, T12 fluorescent luminaries and mercury vapor units. The manufacturer considered a fluorescent system but opted for a high bay HID system with electronic ballast because fluorescent luminaires are highly sensitive to heat.
The HID system installed, which uses 315-watt ceramic metal halide lamps, has a UL/CUL 55ºC ambient listing and can withstand the facility’s excessive heat, which is even worse during the summer. The manufacturing facility also benefitted from the luminaires’ extended 5-year warranty.
Lighting fixtures are available that are marine and IP66 rated to protect against the harsh elements found in hazardous environments and facilities such as food processing plants where hose downs occur daily.
Tamar Williamson's full article, ‘Illuminatig the Path To Savings' is one of the topics in Plant Engineering’s Forecast issue, which will be published in mid-February. To receive the digital edition of Plant Engineering in time for the Forecast issue, which also will feature the 2011 Plant Engineering Salary Survey, click here: