Often task lighting refers to increasing illuminance to better accomplish a specific activity. 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. Because task lighting provides focused light where needed, general lighting can be reduced.
Different strategies for task lighting exist. The three main approaches are:
· Localized average lighting, where a lamp supplies both ambient light and task light
· Asymmetric task light, where the lamp is placed at the side of the work area
There is a renewed interest in task lighting. “Renewed” because task lighting was all the world had known before our dependence on high-output overhead fixtures. Prior to electrically powered lighting fixtures, seeing at night was accomplished through the use of “task lights” such as candles and oil and kerosene lamps.
When the power of electricity was first harnessed, it was applied to crude incandescent “task lights.”
For many years, task lighting continued to be the best option for seeing indoors. It was a long time before overhead fixtures would make a significant impact on how work areas were lighted.
First, the technology had to be developed so that overhead fixtures could produce adequate amounts of quality light. For buildings that had been built prior to the application of electricity, it was difficult to integrate overhead lighting into the old structures. Finally, architects had to discover how to efficiently incorporate overhead lighting into new buildings.
Despite obstacles to subduing our need for task lighting, it was convinced that task lights were not necessary in the presence of powerful overhead fixtures. We were shown that adequate foot-candles on the desk top could be produced from overhead lighting – but at what cost?
In recent years we have begun to discover some of the costs of total reliance on overhead lighting to illuminate the work surface. The key is total reliance.
The best approach for designing an energy-efficient and visually comfortable lighting installation is effective integration of overhead and task lighting.
There are also other approaches to 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. Task lamps are also used for many home tasks such as sewing, reading, small repairs, model construction, crafts, writing, and many other activities. 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
Benefits for individuals.
Task lighting and productivity. Much research has been conducted on the relationship between lighting conditions and worker productivity. Surveys continue to find that poor lighting and eyestrain are frequent worker complaints. Although it may be difficult to demonstrate a direct cause-and-effect relationship between lighting and performance in real world settings, we can make some common sense observations.
First, we must be comfortable to maintain productivity over the course of a day. There are enough demands and distractions that compete for our energy and concentration. Straining to see should not be one of them.
Seeing should be effortless and automatic. We spend a great deal of time and money trying to make ourselves comfortable so that we can be more efficient and productive. Yet frequently, proper lighting is neglected. If lighting is so poor as to make workers uncomfortable, then efficiency is going to decrease over the long term.
However, once lighting reaches a “critical comfort level,” better lighting above and beyond that level will probably not increase productivity. Once lighting surpasses the critical comfort level, many other environmental factors interact to influence productivity.
LOCALIZED AVERAGE LIGHTING
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. Recessed lights placed directly over the work area are another common example.
MAGNIFYING TASK LIGHTS
Some task lights also come with built in magnifying glasses for detailed tasks. It is hard to overstate the benefits of having focused light alongside magnification for small, precise operations such as model building, sewing, or other high-detail activities. Dentists often use a task light with magnification to perform dental cleanings.
FREELY ADJUSTABLE TASK LIGHT
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.
A common form of home task lighting is a goose-neck lamp or swing arm light fixture. The adjustable neck allows light to be focused on the exact task needed, and the swing-arm wall sconces can be positioned next to a bed or chair, and adjusted to shine light on a printed page. Free standing, adjustable desk lamps are commonly used in home office applications.
ASYMMETRIC TASK LIGHT
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 irrespective 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.
FIXED TASK LIGHTING
Fixed task lighting refers to a non-movable light source dedicated to lighting a specific task. In kitchens, a homeowner may install several recessed “can” lights or under cabinet lighting to provide clear lighting onto the counters for cutting and preparing food. Having proper lighting when working with sharp knives is a critical component of injury prevention. Another form of fixed task lighting may simply be a table lamp positioned over one’s reading chair.
Basic Types Of Lighting
Three are three basic types of lighting that work together in your home:
1. Ambient (general lighting)
A good lighting plan combines all three types to light an area according to function and style.
Ambient lighting provides an area with overall illumination. Also known as general lighting, it radiates a comfortable level of brightness without glare and allows you to see and walk about safely. In some spaces such as laundry rooms, the ambient lighting also serves as the primary source of task lighting.
It can be accomplished with chandeliers, ceiling or wall-mounted fixtures, recessed or track lights and with lanterns mounted on the outside of the home. Having a central source of ambient light in all rooms is fundamental to a good lighting plan.
Task lighting helps you perform specific tasks, such as reading, grooming, preparing and cooking food, doing homework, working on hobbies, playing games and balancing your checkbook. It can be provided by recessed and track lighting, pendant lighting and undercabinet lighting, as well as by portable floor and desk lamps.
Task lighting should be free of distracting glare and shadows and should be bright enough to prevent eye strain.
Accent lighting adds drama to a room by creating visual interest. As part of an interior design scheme, it is used to draw the eye to houseplants, paintings, sculptures and other prized possessions. It can also be used to highlight the texture of a brick or stone wall, window treatments or outdoor landscaping.
To be effective, accent lighting requires as least three times as much light on the focal point as the general lighting surrounding it.
Accent lighting is usually provided by recessed and track lighting or wall-mounted picture lights.
TASK LIGHTING AND MAGNIFICATION.
Do we need a task light if we have magnification? The answer is yes, because magnification is only half the solution for achieving good vision.
Proper task lighting allows us to get the maximum benefit from a visual aid, and may even allow for reduced magnification. Increasing the amount of light (brightness) directed onto a task will help compensate for small print size or poor contrast. Examples of poor contrast include faded print on white paper, dark print on a dark background, or dim characters on a computer screen
Proper lighting is of equal importance. Take an extreme example. How much good would magnification do in the dark? The benefits derived from visual aids such as magnifiers and prescription glasses are entirely dependent upon the lighting conditions in which they are used.
BOTTOM-LINE BENEFITS FOR BUSINESS.
The use of a lighting system which integrates task and overhead lighting can have a direct impact on the bottom line by lowering utility dollars.
Instead of trying to maintain proper lighting levels on desktops from overhead fixtures, task lights can do a better job in providing adequate foot-candles. A task light using an 18-watt compact fluorescent will consume far less energy than a typical overhead lighting fixture.
A work environment can maintain lower levels of overhead light by illuminating desktops with energy-efficient task lights. For examples consider an office with 16 workstations illuminated by 16 overhead fixtures each with four T8 32-watt fluorescents. The total wattage when all fixtures are operating is 2,048. If each fixture used two T8 instead of four, and each workstation was equipped with an 18-watt task light, energy consumption would be reduced by 36 percent!
A recent example demonstrates the energy waste that occurs all too frequently. An office manager remarked that, “we don’t need those (task lights) to control glare on our computer screens. We installed these filters on the screens to block out glare.” This makes no sense in terms of cost reduction and energy conservation. First flood the room with light and then block it out with filters. It is like turning the heat up to 90 degrees in the winter and then opening the window to maintain the right temperature.
Other ways in which the use of task lighting can help control costs are by reducing maintenance costs. Task lights are easy to install, keep clean, and change bulbs. When offices made from wall partition furniture systems are rearranged, task lights are easily moved. Proper lighting is achieved without much worry about the location of overhead fixtures.
TASK LIGHTING AND VISION DIFFERENCES.
Our ability to see differs from person to person, and within ourselves, on different occasions. When we are tired or sick, we may see less well than when we are healthy and fresh.
The visual capabilities of individuals of the same age can vary greatly. Older people need substantially more light to see than younger people. Research indicates that the visual performance of those in their 20s is about eight times better than those in their 60s, and almost four times better than those in their 50s.
This increased need for light is due to a number of biological facts in the aging process. For example, the muscle in our eye called the iris, expands and contracts to control the amount of light entering our eye. As with all our muscles, the iris loses some of its flexibility in the aging process, and doesn’t open as wide. More light is needed to compensate for the reduced ability of the iris to open wide.
Not only are there obvious vision differences between people, but different tasks have unique lighting requirements. Lighting demands for a video display terminal (VDT) operator are different from a proof reader, which are different from a graphic artist working at a large table where accurate color perception is critical.