Often task lighting refers to office lighting, where the task light is used to increase illuminance on the reading area. However, the illuminance level is not the only factor governing visibility. Contrast is also important, and a poorly positioned light source may cause contrast reduction, resulting in loss of visibility. Therefore, it can be argued that the most important purpose of task lighting in the office is not increasing illuminance, but improving contrast.
Different strategies for office task lighting exist. The three main approaches are:
There are also other approaches to office task lighting, for example under-shelf luminaires.
Other instances of task lighting are in machinery, where a specific work area needs illumination, and in workshops, where a task light may illuminate the actual working area. Special instances of task lighting are examination and operation lights for medicine and surgery, as well as the dentist's lamp. The actual task may range from very small up to about as far as you may reach with your hands or available tools. Lighting of larger areas is beyond the scope of task lighting.
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Localized lighting consists of a luminaire that provides ambient light as well as task light. Often it is an uplighter with a light source that is directed downward. It is intended to be mounted immediately over the workplace, and it can be either hung from the ceiling, mounted on the desk or a dividing wall, or it can be a free-standing floor lamp.
The main feature of the freely adjustable task light is evident; one may adjust it freely at any whim or to suit one's needs. The lamp presents few limits to how one may position or orient the light. A freely adjustable lamp may include means for glare control, as a honeycomb or parabolic louvre that restricts the light output angle.
The asymmetric task light is intended to be placed at the side of the actual task. The luminaire directs the light obliquely over the desk, with the highest illuminance typically about 1' to 1½' to the side of the lamp head. It mostly has an arm system that holds the lamp head horizontally irrespectively of the arm movement - a parallel arm. Asymmetric lamps often cause more reflected glare than other lamps. In workplaces where people use different table heights, an asymmetric lamp may cause direct glare due to its absence of means for glare control (ref:1).
Contrast reduction in the office workplace refers to reading objects having decreased contrast compared to an estimated ideal contrast. If a lamp is placed so that printed letters reflect some of the light, their contrast against the paper background will decrease. This happens when a light source is reflected as in a mirror from the print into the eyes of the observer. A poorly placed lamp may render text illegible, regardless of illuminance level.