Fundamentals of Paint Spray Booth Lighting
Posted Friday, April 30, 1999
Written by Mike Singer, as seen in Metal Finishing, May 1999
Selecting the proper lighting For spray booth applications is critical to help optimize quality of workmanship and productivity. The type and size of the booth also has a direct bearing on the number, type, and size of the light fixtures needed to achieve proper lighting conditions. In general, the larger the size of the booth, the increased number of fixtures needed.
The most common type of lighting used in paint spray booths are panel mounted fluorescent lighting fixtures. The fixtures are actually mounted and recessed in the booth panels. These fixtures are commonly Class I, Division 2 or Class I, Division 1 rated fixtures and are third party listed for hazardous locations. Class I, Division 2 locations are those where volatile flammable liquids or gases are handled, processed, or used. Normally, they will be confined within closed systems from which they can escape only in the case of rupture or deterioration of the systems.
Panel mounted design provides a simple and efficient means of installation. These fixtures are typically constructed of either 18 or 20 gauge steel construction. Coupled with a white baked enamel finish, a durable and highly reflective fixture finish is created. A clear, tempered safety glass lens is sealed and gasketed to ensure a durable, long lasting seal against vapor, dust, and moisture. Commonly used fixtures of this type used in paint spray booths are 4 lamp, 4-foot fixtures with 32, 40, or 60-watt HO lamps, with 40-watt lamps being the most commonly used. The fixtures will normally have an inside, rear, or dual inside/rear access hinged door panel for the purpose of servicing the lamps and ballasts.
In fixtures with an inside access, an interlock switch is provided and is to be wired in such a way as to disable paint spray equipment when the inside access panel is opened. This enables the fixture to be mounted in spray booth panels without the previously required second lens. In instances where a non-hazardous rated fixture is used, these must be mounted behind a sealed stationary mounted lens. These fixtures can only be serviced from the outside of the booth.
Hazardous rated fixtures must, by code, be used in areas that extend from the edges of any opening of the booth in accordance with the following:
- If the exhaust ventilation system is interlocked with the spray application equipment, then the Division 2 location shall extend 5 feet horizontally and 3 feet vertically from the open face or open front of the booth.
- If the exhaust ventilation system is not interlocked with the spray application equipment, then the Division 2 location shall extend 10 feet horizontally and 3 feet vertically from the open face or open front of the booth. The term interlocked means that the spray application equipment cannot be operated unless the exhaust ventilation system is operating and functioning properly and spray application is automatically stopped if the exhaust ventilation system fails.
If fluorescent light fixtures are actually mounted inside a paint spray booth and are not recessed panel mounted, then Class I, Division 1 explosion proof fixtures must be used. These fixtures are typically available with 2, 3, or 4 lamps in 2 foot or 4 foot length fixtures. A Class I, Division 1 location is defined as where hazardous atmosphere may be present during normal operations. It may be present continuously, intermittently, periodically, or during normal repair or maintenance operations, or those areas where a breakdown in processing equipment releases hazardous vapors with the simultaneous failure of electrical equipment.
When actually selecting light fixtures for a paint spray booth, it is important to think about what you want to achieve and to get an even distribution of lighting in the booth. There are many factors that can influence lighting levels in a spray booth application. In order to help select the right fixtures, the following information is important to know:
- Is the application retrofit or new?
- What are the inside dimensions of the booth? (To include width, length, and depth.)
- What is the specific booth design?
- If a retrofit situation, what are the type and number of existing lights in the booth?
- For servicing, do you want the lights to be inside access, outside access, or both?
- Does the existing booth have a hipped ceiling? If yes, what is the hip size and degree? Are there lights in the hip, and is it possible to add lights to the hip?
- Does an existing booth have corner chambers, and what are the sizes?
- What construction is the booth floor?
- What materials are used for booth construction in the floor, walls, and ceiling, and what are the specific colors?
- Are there man-doors in the booth walls? If so, where?
- Are there any windows or translucent panels? If so, where?
- Are the filters located in the floor, ceiling, or booth walls?
- What types of products are normally painted?
- What are the shapes of the products (square, round, rectangular, etc.)?
- What is the largest object in terms of width, height, and depth?
- What is the smallest object in terms of width, height, and depth?
- What colors are primarily painted?
With this information, light fixture manufacturers can use computer programs to help determine the recommended number and placement of the fixtures.; As a rule of thumb, 100 foot-candles at a 3-foot height has been a general industry standard. If a different foot-candle level is desired to be maintained at a different height, this should be communicated to your lighting supplier. Light intensity measured on a plane, at a specific location, is referred to as illuminance. Illuminance is measured in foot-candles, which essentially are lumens per square foot. Other factors such as reflectance of surrounding surfaces, fixture efficiency, and lamp lumen output can influence the type and quantity of needed light fixtures. As mentioned earlier, the size of a paint booth also can influence the size of the fixtures. In larger booths, such as truck paint spray booths, 4 lamp, 8-foot length fixtures featuring 95 or 110-watt HO lamps are sometimes desired. The type of a booth can also influence the choice of fixtures. Slim light fixtures that feature a compact design, which are just 2 1/4-in. fixture depth, allow for mounting in an insulated panel.
The ability to see colors properly is another aspect of lighting quality. Light sources vary widely in their ability to accurately reflect true colors of objects. The color rendering index (CRI) scale is used to compare the effect of a light source on the color appearance of its surroundings. A scale of 0 to 100 defines CRI. The higher the color rendering index, the less color shift or distortion that occurs. As an example, a standard cool white T12 (1.5' diameter) fluorescent lamp with a Kelvin temperature of approximately 4100oK has a CRI of 62, which is considered low. Where quality or color matching is important, a higher CRI rated lamp will normally be needed. As a general rule of thumb, the higher the CRI, the lower the efficiency of the lamp. It is important that a balanced approach be used when considering CRI, lamp lumen output, and efficiency of the lamp.
For many years, the lighting standard has been F40T12 fluorescent lamps. These are 40 watt, 1.5' diameter lamps. Through technological advances, lamps have been developed that consume less energy, produce better quality and higher levels of light, such as T8 (1' diameter) lamps. The T5 (5/8' diameter) lamps, which are starting to be introduced to the U.S. market, show even more promising results concerning maintained lumen output over the life of the lamp, energy savings, and they operate more efficiently at higher ambient temperatures than T8 or T12 lamps.
Once the light fixtures have been installed in the spray booth, care must be taken to prevent dirt accumulation and paint over-spray buildup on the fixture lenses. If not removed on a continual basis, this will degrade the overall lighting quality in a booth. A simple, effective light fixture lens covering is cling-on plastic film. This is a 3 mil plastic with a custom acrylic adhesive in 12" and 18" widths. It is easy and quick to install and remove. A total re-lamping program should also be considered as lamps reach the end of their life.
In conclusion, lighting selection in a paint spray booth should not be taken for granted. Different applications can require different light properties. To correctly match the proper lamp, ballast, and fixture combination, you should consult and work closely with your lighting supplier before making your lighting selection. One such manufacturer of fluorescent lighting for paint spray booths and hazardous industrial locations is LDPI Lighting, 4404 Anderson Drive, Eau Claire, Wisconsin 54703. They specialize in this area and are an acknowledged industry leader in providing lighting solutions for paint booths and hazardous industrial locations. Their toll free telephone number is 800-854-0021, and their fax number is 715-839-8145. Their website is www.ldpi-inc.com and email address is firstname.lastname@example.org.