Conducting a Lighting Audit

A lighting audit is an investigative process that measures conditions against standards to determine where cost-effective changes can be made. Below is a brief description of the steps to be followed when conducting an energy audit for lighting.

The first step is a walk-through of the plant to observe the quantity and quality of available light. Problems are noted such as an area where lighting levels are too high, where lights are left on unnecessarily, or where factors leading to visual discomfort may inhibit productivity or safety. The type, quantity, location and height of lamps and fixtures are recorded. Detailed measurements of illumination levels are taken with a lightmeter, both at task areas and for general overall lighting. Next, simple retrofit possibilities, such as switching from general lighting to task lighting are considered. For example, by simply lowering the fixture height, a lighting system can be changed from general to task-oriented with a desirable increase in contrast between the task area and the general workplace. Also, painting equipment slightly lighter than the surrounding area adds contrast and aids workers in discerning moving parts, thereby increasing safety. Possible areas for these improvements are noted during the audit.

After all the simple retrofit options are examined, a plan for the general modification of the plant lighting is devised. Such a plan integrates simple modifications and major improvements into a cohesive, energy efficient system.

Options to Consider for Reducing Lighting Costs

Regular Maintenance

Periodic cleaning of dusty bulbs and fixtures can save up to $1 in lost illumination per four-lamp fixture per month. A thorough lamp maintenance program can extend lamp life and improve lighting levels by up to 30%.

Lamp Replacement

Fluorescent lamps should be replaced at the end of their useful life (defined as 70% of the rated life), since lumens-per-watt rating starts to decline at this point, lowering overall light levels.

Lower Fixtures

Lowering ceiling fixtures to bring them closer to the workspace increases the amount of available light focused on the task. If the distance between fixture and work plane is 10 feet or more, further investigation may be required.

Repainting

Overall lighting efficiency is directly affected by the color of the ceilings, walls, equipment and other surfaces in the workplace. Selecting lighter, more reflective colors when repainting can enhance contrast and promote safety by increasing the amount of available light.

Daylighting

Installation of skylights in conjunction with automatic dimming devices can yield significant savings in some environments. However, the use of natural light from windows and skylights requires a thorough analysis, both from a lighting and heating/cooling standpoint. Consult the IES Lighting Handbook, 1984 Reference Volume, and 1987 Applications Volume for more information on this option.

Control Devices

The installation of various lighting control devices can reduce energy costs. Recent technological advances in industrial lighting system components and controls make it possible to reduce consumption significantly through scheduling and automatic control. Consult lighting vendors for more information.

Lamp Conversion

Converting to more efficient light sources offers excellent savings potential. For example, experience with industry indicates that the cost for replacing incandescent lamps with efficient fluorescent fixtures can pay for itself within two years through avoided energy expenses.

Convert to Energy Efficient Fluorescent Lamps

One attractive alternative for energy conservation is replacing existing fluorescent lamps with the new lower wattage energy efficient ones. Generally, the new lamps are of lower light output and the light level will be reduced by about 3 to 5% (usually not detected by the human eye). However, the wattage reduction will range from about 15 to 20%.

Most present day lighting standards derive from the IES and ANSI criteria. Using lighting levels set by these organizations as baseline information, many industries have successfully adopted lower illumination levels without sacrificing any of the benefits of good lighting. While the energy-savings possibilities may be attractive, other factors must be considered. In particular, employees involved in certain types of tasks find the light coloration from some of the more efficient sources (particularly high pressure sodium) objectionable, so that use of the most desirable economic option may not be possible. Consultation with manufacturers and lighting consultants will often prove helpful.

Lighting Terms

Brightness - the intensity of the sensation which results from viewing a surface or space which directs light into the eyes.

Color Rendition - the effect of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference or standard light source.

Contrast - the relationship between the brightness of an object and its immediate background.

Distribution - the dispensing or spreading of light over a surface.

Ellipsoidal Reflector Lamps - incandescent lamps designed to be placed in canister fixtures; they direct more light out of the fixture.

Footcandle - the basic measure used to indicate level of illumination. One footcandle (fc) is equal to one unit of light flux distributed evenly over a one-square foot surface area. (See lumens).

High-Pressure Sodium - the most efficient light source of the high intensity discharge family. It provides a light golden color and long life.

Low-Pressure Sodium - presently the most efficient light source available. Applications are limited because of its poor yellow color.

Lumens - the measurement of light flux produced by a lamp, as opposed to footcandles which represent the amount of all light - reflected or otherwise - within one square foot.

Lumens-per-watt - the relative measure of efficiency (referred to as efficacy) of a light source, calculated by dividing the light output (lumens) by the electrical power input to produce that light (watts) for a given lamp type.

Metal Halide - an efficient high intensity light source with crisp, white color.

Task Lighting - lighting that falls on a given viewing task or object, supplementary lighting as opposed to general overall lighting level.