Environmental Health & Safety

Office Lighting

Illuminance
A good starting point for proper lighting is to ensure that there is an appropriate amount of light. Too much light will increase glare, and to little light will cause eyestrain. Illuminance can easily be measured and is part of the standard ergonomic evaluation. It is generally recommended that a video display terminal have an illuminance of 200 to 500 lux. If a workstation is too dim for paperwork, task lighting may be used to increase the illuminance of the area that is used for paperwork. It is also important to note that older individuals may need more light than younger individuals to comfortably complete the same task.

Glare
Glare can result in eyestrain, as well as affect posture. To minimize glare, walls and surfaces should consist of a matt, neutral color. Lamps should be constructed and placed so the operator does not look directly into the bulb or see its reflection in their display. Overhead fluorescent lights should be equipped with a low glare lens or louver for the same reason. If windows are present, the best positioning of the display is perpendicular to the window. This controls glare on the monitor and prevents the backdrop behind the display from blinding the operator. Direct sunlight may increase glare; a good solution is to ensure that the windows are equipped with operable blinds.

Incandescent Lighting
Light from incandescent bulbs is generally pleasant because it has much in common with sunlight. Unfortunately, incandescent bulbs burn hotter, are not as efficient, and are not as convenient as fluorescent tubes.

Fluorescent Lighting
The spectrum of light from a traditional fluorescent lamp is different from sunlight, often decreasing satisfaction with the quality of light. That is to say, fluorescent lighting is much cooler, more efficient, and more convenient than incandescent lighting; though, it may not be as pleasant. Additional characteristics should be taken into consideration with respect to fluorescent lighting:

1. Color Temperature
   Color temperature refers to the color of light which is emitted from a fluorescent tube. Tubes with a color temperature close to 3000K will have a "warm," orange quality to the light, whereas tubes with a color temperature close to 5500K will have a "cold," silver-blue quality to the light. Color temperature is usually stamped on the fluorescent tube. Otherwise, if the type of lamp is known, the specs should be easy to find.


2. Color Rendering Index
   The second characteristic is the color rendering index (CRI). This is a measure of how accurately a fluorescent light will render the true colors of objects. The CRI consists of a number that is usually stamped on the lamp or easy to look up; it will range between 50 and 99. A lamp with the CRI of 99 renders colors close to that of sunlight. Standard fluorescent tubes generally have a CRI of 75 to 80. For about four times the cost of traditional fluorescent tubes, fluorescent lighting can be replaced with that of a CRI greater than 90. Mixing daylight or incandescent light with fluorescent light will generally work to improve the light balance of a space.

Fig. 2. Comfortable fluorescent lighting consists of a balance between illuminance, color temperature, and the color rendering index.