Industrial-strength lighting

Although power, grounding, and controls take center stage in electrical design for the industrial environment, the challenges involved with lighting industrial spaces often are overlooked. These challenges include:

• Making room and locations for the larger fixtures that typically are required for explosion-proof environments

• Maintaining adequate lighting levels in wet or hose-down environments

• Maintaining adequate lighting levels in high-vibration environments

• Maintaining light fixtures in high-bay environments

• Having instant illumination in high-bay environments while maintaining adequate lighting levels

• Ensuring that light fixtures don’t disrupt the integrity of cleanroom environments

• Identifying multiple suppliers who are able to supply design-compliant light fixtures when the owner’s contracting procedures require more than one manufacturer for materials

• Providing energy-efficient lighting control schemes within industrial environments.

A case study for an aerospace company illustrates how one team of lighting designers overcame a number of these challenges. The project entailed replacement of lighting inside a seven-story, Class 10,000 cleanroom, acoustical and vibration chamber, where aerospace equipment is tested, with a maintenance catwalk on each level. To add to the mix, the ground floor area inside the chamber was a Class 1, Division 2 hazardous environment.

The existing lighting inside the chamber, designed in 1984, consisted of 15 400 W metal-halide floodlights centered on each of the three permanent walls and located 14 ft above the floor and 10 ft above each of the maintenance catwalks. The lighting was not uniform due to the shadows created by the catwalks and catwalk supports. In addition, the lighting levels did not meet cleanroom lighting standards of a 100 ft candles average. Instead, the lighting varied between 10 ft and 15 ft candles when measured in the middle of the chamber and less then 10 ft candles at the perimeter walls.

In discussions with the user and the facility department, a number of lighting criteria were established:

• Cleanroom-rated fixtures must be specified

• Cleanroom lighting levels must meet an average of 100 ft candles on the ground and at each maintenance catwalk

• Lamp failures caused by acoustical and vibration tests should be eliminated

• No out-gassing materials, including silicone, should be used in the lighting fixtures

• Explosion-proof lighting must be used from the ground floor up to 14 ft above the floor

• Ballasts for all fixtures should be remotely mounted

• Maintenance of the lighting system should be as simple as possible.

The challenge

The industrial setting posed three challenges: the cleanroom environment, the hazardous environment on the ground floor and the high sound/vibration environment. Lighting manufacturers do not perform acoustic or vibration tests on their equipment. In addition, no standard judges how well lighting equipment will withstand a certain sound level. Select fixtures, however, are manufactured for use in environments that have higher levels of vibration and shock. To determine an appropriate solution, the team examined two different lighting systems manufactured for use in similar environments.

The first system is a cleanroom-rated light fixture containing an induction fluorescent lamp rated at 150 W and 12,000 lumens. This fixture was chosen as an option because of its ability to withstand high vibrations, including installation under train platforms for the Chicago rail system. The light fixture contains a small amount of silicone in the induction lamp housing, but will not out-gas and the ballasts can be remotely mounted at a distance of up to 66 ft. See Table 1.

Given that the ballasts for the lowest row of fixtures are above the top of the chamber at a vertical distance of 57 ft from those fixtures, it was likely that the ballasts for the lower rows of fixtures are in an adjacent space. The additional horizontal distance to that adjacent space would be greater than 66 ft.

The second option is a metal-halide floodlight rated at 400 W and 34,000 lumens. Made for the mining industry, the light fixture contains a vibration-dampening lamp socket supported by a multi-plane diaphragm to absorb shock and vibration, and is rated for both clean rooms and hazardous environments. The ballasts also may be remotely located 75 ft or closer without any issues, and the lights located near the catwalks to allow for ease of maintenance. The lamp socket and lens gasket contain high-temperature silicone and EPDM rubber, but do not out-gas. See Table 2.

Design conclusion

The team recommended floodlights because this light fixture is manufactured for high-vibration, hazardous and clean-room environments without modification. In addition, the lower quantity of light fixtures would be less expensive to install, and the fixture count and locations would more closely match existing conditions, allowing the contractor to reuse much of the existing conduit and wire. Also, costs associated with the decreased lamp life would be offset by the lower maintenance costs.

The end user agreed, but also thought that light output consistency should be given greater weight. The end user requested a hybrid design using the Class 1, Division 2 floodlights at the ground floor where the hazardous environment exists and the incandescent fluorescent light fixtures at levels 2 through 5. Within a year the chamber had undergone five full-cycle vibration and acoustic test cycles, and most of the incandescent fluorescent light fixtures showed some signs of failure. As a result, the fixtures were removed and examined. The examination led the team to conclude the incandescent fluorescent light fixtures could not handle the acoustic environment. Fortunately, the fixture failures were noticed before the fixtures completely failed and did not result in any damage to expensive, time-sensitive aerospace equipment.

Because the flood lights at the ground floor showed no signs of failure or fatigue, the lighting designers suggested installing them throughout the chamber. Discussions with the end user revealed that the sound level is 2 dB higher at the fifth floor compared to the ground floor, and a 3 dB level increase is equivalent to doubling the sound level. Because of the dB level increase, the recommendation was to install a few floodlights at each level and subject the fixtures to at least five full cycle tests.

Lessons learned

Based on this project, the team offers a number of general suggestions:

• A light fixture or similar device should not be specified unless the light fixture or electrical device is proven to work in the environment

• If necessary, subject the fixture or device to the environment for testing prior to installation

• Try to identify all design concerns and environment conditions at the start of the design process to avoid specifying a light fixture or similar device not rated for the environment.

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