Warehouses using rack storage systems present unique lighting design challenges particularly for retrofits intended to improve the lighting scheme.
The layout of most product storage warehouses comprises a shipping and receiving area (may be the same or separate areas), a low, open storage area for bulky items and a high rack storage area, usually occupying most of the warehouse space.
Rack storage systems are often built to take advantage of high ceilings. Forklifts (or robotic automated systems) may be required for stocking and retrieval of product located high in the rack system.
Here are some design concepts to consider when upgrading existing warehouse rack storage lighting.
The lighting design for warehouses is unique in that it is not based on the overall size of the warehouse, but on the configuration and dimensions of the rack area. The width of the aisle, the length of the aisle and the height of the rack will primarily, but not exclusively, determine the lighting requirements.
Light Distribution & Illuminance
Most of the visual tasks involve reading box labels, sorting, inspecting, picking products, stocking products. These visual tasks occur primarily on a vertical plane. Therefore the lighting design should focus on providing sufficient light vertically, from top to bottom, in the rack system.
High bay fixture spacing, no matter what the light source, is critical. If the spacing is too great, illumination "drop-off" will result. If it is too tight, glare may be a problem near the top of the racks. The use of asymmetric distribution fixtures will also help improve the uniformity of light vertically and should allow for increased fixture spacing.
The Illuminating Engineering Society of North America's (IESNA) target illuminance recommendation in the rack area of the warehouse is 20 to 50 average maintained vertical footcandles. Within this range, the specific illumination requirements will depend on several factors.
Interior Ceiling & Floor Reflectance
Warehouse ceiling and floor reflectance factors influence the lighting requirement. Light colored ceilings and floors can dramatically increase the overall illumination, allow lower light output fixtures (to save energy) and also provide a more pleasant work environment. If the warehouse has skylights, higher ceiling reflectance will reduce the contrast between the skylights, fixtures and ceiling.
For warehouses, the IESNA recommends a ceiling reflectance factor of 60% and a floor reflectance factor of 40%.
Size of Inventory and Readability of Labels
Generally, the physical size of items in the racks affects the illumination requirement. Large, bulky items usually require less light than small, hand size items like equipment parts. However, if the warehouse crew needs to read the labels on the stored inventory, the print size and contrast on the labels affects the lighting requirement more than the physical size of the inventory. To assure accurate reading of labels from top to bottom in the racks, sufficient light must be available to easily read the smallest font size typically found on the inventory.
Color Temperature of the Light Source
There are preliminary research results showing that higher color temperature light, in the 5000K range, may provide better visual acuity. Higher color temperatures also provide a perception of increased brightness.
Use 4100K to 5000K light sources to improve accuracy and make the task of reading labels easier.
Fluorescent: Use T5HO or high performance T8 with electronic ballasts. Only consider standard T8 or energy saving T8 lamps for ceiling heights of 10 feet or less such as over packing and shipping tables. T5HO lamps are preferred when choosing fluorescent in high ceiling warehouses. They produce up to twice the lumen output of T8 lamps and the smaller diameter tube optimizes the distribution of light from the fixture reflector to the floor in high mount applications. If fluorescent high bay fixtures are being used, consult the photometric report to determine if the light will reach the lower shelves of the stack. In addition, use tandem 8 ft. fixtures rather than 4 ft. fixtures to get a more even distribution of light up and down the aisle. Fluorescent lamps are temperature sensitive, so it's important to know the fixture manufacturer recommendations for use in cold or hot warehouses.
Metal Halide: With high wattage metal halide lamps it is important to guard against glare. Operators working in the racks could experience severe glare when looking up to the tops of stacks. In some situations, HID fixtures that provide direct / indirect lighting with a strong uplight component can enhance the visual environment dramatically. This type of fixture should be tested in place to assure enough illumination reaches the lower levels of the rack.
LED: The increasing availability of LED high bay fixtures offers another option for warehouse lighting. LED provides the benefits of saving on energy costs and lower maintenance costs compared to fluorescent and metal halide. At the same time, the use of LED should not compromise the quality of lighting design for satisfying the work task requirements of the warehouse workers when compared to other light sources.
Safety & Security
While illuminating rack storage areas may be the highest priority in a warehouse lighting upgrade, other issues that should be part of the lighting design include worker safety and security. In warehouses with many workers and numerous pieces of equipment such as forklifts moving in and out of aisles, care should be taken to ensure sufficient light levels exist particularly at high traffic intersections. In warehouses where security issues such as restricted access and monitoring are important, the lighting levels may need to be specifically determined for designated areas.
For a more detailed discussion of lighting design and energy savings for warehouses, see the IESNA book "Advance Energy Design Guide for Warehouses and Self-Storage Buildings."