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.

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.

Use horizontal area lighting for sides of buildings, signage, walkways, entrance approaches, access roadways, and driveways.

Use vertical area lighting for parking lots, sides of buildings, signage, storage tanks, and platforms.

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.

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.

Vertical aiming

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 ¾ the distance across the area to be illuminated, or twice the luminaire mounting height, whichever is the lowest value. Higher aiming angles do not improve utilization or uniformity.

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.

Horizontal aiming

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).

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:

• High efficiency
• 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.

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.