Outdoor lighting considerations
Whether lighting the front office facade, employee parking lot, storage yard, or flagpole, outdoor lighting requires that plant engineers follow certain guidelines.
Outdoor lighting should be more than just decorative. Safety, security, functionality, and efficiency should be considered when designing and specifying lighting systems for a plant’s exterior.
For starters, drive by the plant after dark. Walk from parking lots to buildings. Audit storage yards, entranceways, material handling yards, and other potential work areas, making note of light levels and shadowy areas.
After identifying the weak areas, inventory the current outdoor lighting array, paying close attention to security or spill-light issues. Surveillance cameras and security personnel depend on adequate lighting. Quantify current lighting levels and determine where it is necessary to supplement or replace fixtures.
Use industrial floodlighting to illuminate storage yards, tanks, signs, substation and transformer yards, and vital structures.
Use wall lighting for entranceways, loading docks, signage on sides of buildings, and platforms.
Decorative pole-top lighting
Use decorative pole-top lighting for walkways leading to front offices, access roadways, and driveways.
Use decorative floodlighting for facades, displays, flagpoles, and corporate signage.
Horizontal area lighting
Use horizontal area lighting for sides of buildings, signage, walkways, entrance approaches, access roadways, and driveways.
Vertical area lighting
Use vertical area lighting for parking lots, sides of buildings, signage, storage tanks, and platforms.
Cutoff area lighting
Use cutoff area lighting to avoid spill light and glare on adjacent properties and roadways. Sharp cutoff lighting is used in medium and large areas such as parking lots, storage yards, and material handling areas that border roadways, walkways, or other plants or property.
Mounting pole selection
When lighting horizontal areas such as parking lots and material handling yards, engineers must specify luminaire mounting height on poles, pole height, number of poles for the area to be illuminated, and pole placement.
The distance between poles should not exceed four times the mounting height. This ratio applies to the distance across a lighted area as well as lateral distance between poles. This guideline applies regardless of the number of floodlights per pole, the level of illumination desired, or the type of light source (incandescent, fluorescent, or HID lamps).
Center pole systems can be used when lighting large areas at illumination levels up to 5 fc. These center poles should be within a distance of two times the luminaire mounting height from the sides of the area to be illuminated.
Side poles should be no more than two times the luminaire mounting height from the corners.
Definition : Footcandle (fc) is a unit of illuminance. One fc is one lumen (lm) per square foot, or: 1 lm/ft 2= 1 fc
Lighting poles must support the luminaires and their mounting hardware. Poles also must be sturdy enough to withstand the highest wind velocity expected for a given location. Each vendor of outdoor lighting provides selection recommendations based on luminaire type, pole loading, total loading, effective projected area (EPA), and geographic location.
General rules for lighting vertical surfaces differ from those for horizontal areas. Illumination uniformity is necessary for vertical surface lighting.
For normal area lighting, the aiming point should be 2/3 to
Lighting on vertical surfaces is often as important as horizontal lighting — especially for outdoor work area or security lighting. The vertical illumination in line with the floodlight is determined by this ratio:
horizontal mounting distance:mounting height
For example, if the horizontal distance is twice the mounting height, the vertical illumination is twice the horizontal distance.
Floodlights with NEMA 6 or 7 horizontal beams effectively light an area at least 45 deg to either side of the aiming line. Perimeter poles require at least two floodlights to cover an area in all directions (Table 1).
NEMA beam spreads
|NEMA type beam spread||Horizontal aiming line separation||Recommended max aiming line separation|
|2||18-29 deg||12 deg|
|3||29-46 deg||24 deg|
|4||46-70 deg||40 deg|
|5||70-100 deg||60 deg|
|6||100-130 deg||90 deg|
|7||>130 deg||120 deg|
High-intensity discharge lamps
According to IEEE, a high-intensity discharge (HID) lamp is an electric discharge lamp in which the light-producing arc is stabilized by wall temperature. Advantages of HID lamps include:
Long lamp life
Good lumen maintenance
Compact light source
Good light control by using reflectors and refractors.
HID lamps deionize when the power to them is interrupted or if the lamp socket voltage drops below the amount required to sustain the arc for more than a few cycles. The lamp will not restart immediately because it takes greater voltage to ionize the arc tube vapors while they are hot and under high pressure.
HID restrike and warmup characteristics
HID lamp type Time to reach 80% light output Time to restrike Mercury 5-7 min 3-6 min Metal halide 2-4 min 10-15 min High-pressure sodium 3-4 min 1 min
Recommended outdoor lighting levels for industrial plants are based on data published by the Illuminating Engineering Society. Lighting installations should be designed and luminaires selected based on minimum maintained light levels, rather than initial values. Some of the Society’s recommendations are listed in the table to the right.
PLANT ENGINEERING magazine extends its appreciation to Appleton Electric Co.; Crescent/Stonco; GE Lighting Systems, Inc.; Holophane; and Thomas & Betts Lighting for the use of their materials in the preparation of this article.
Recommended industrial illumination levels
Application/location Minimum average recommended illumination, fc Building exteriors Suburb City Rural Terra cotta, light marble, or plaster 10 15 5 Bedford or buff limestone, smooth buff face brick, concrete, or aluminum 15 20 10 Smooth or medium-gray brick, common tan, or dark field-gray brick 20 30 15 Brownstone, stained wooden shingles, or other dark surfaces 35 50 20 Application/location Minimum average recommended illumination, fc Building exteriors Suburb City Rural Main plant parking areas 2 2 2 Secondary parking areas 1 1 1 Active entrances (pedestrian and/or conveyance) 5 5 5 Inactive entrances (normally locked, infrequently used) 1 1 1 Vital locations or structures 5 5 5 Building surrounds 1 1 1 Loading and unloading platforms 20 20 20 Substation and transformer yards, horizontal general area 2 2 2 Substation and transformer yards, vertical tasks 5 5 5 Storage yards, active 20 20 20 Storage yards, inactive 1 1 1 Industrial yard, material handling 5 5 5 Application Minimum average recommended illumination, fc Signs, bulletin/poster boards, and flagpoles Suburb City Rural Bright surroundings Light surfaces 50 50 50 Dark surfaces 100 100 100 Dark surroundings Light surfaces 20 20 20 Dark surfaces 50 50 50 Coal yards (protective) 0.2 0.2 0.2