Lighting

From Academic Kids

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Architect_lamps.jpg
Architect lamps

Lighting refers to the devices or techniques used for illumination, usually referring to artificial light sources such as lamps or flashlights.

Natural indoor lighting is by windows and skylights.

Artificial indoor lighting is by means of lamps, today usually electric lights, but previously by gas, candles or oil lamps. Modern freestanding lamps typically have a base which holds up a light bulb which is covered by a lampshade. Modern portable lighting is typically a flashlight (also called a torch) running on batteries. Indoor lighting is a form of furnishing, and a critical part of interior design. Likewise, lighting can also be an important part of landscaping.

In cities, streets are often lighted at night, usually by streetlights (also known as lamp-posts). These are a form of street furniture. Smaller or rural roads may not be lit. In major cities, light pollution is of growing concern.

Contents

Lighting design

Since the electrical energy consumed in the lighting system can represent a significant part of the cost of operation of a building or home, there is an incentive to design lighting systems for efficiency and low operating and capital cost.

Design of a lighting facility requires consideration of several design factors:

  • types of tasks for the illuminated area
  • population of the area, users of the lighting system
  • life, capital cost, and operating cost constraints
  • desired appearance, architectural features
  • dimensions (plan and height) of the ara
  • characteristices of the wall finishings (reflective or absorbent)
  • dirt and dust accumulation rate
  • maintenance plan
  • operating schedule of the building
  • electrical codes and building codes
  • preferred voltages and power supply

Organizations such as the Illumination Engineering Society and the American National Standards Institute publish guidelines, standards, and handbooks that allow categorization of the ilumination needs of a project for many common design situations. Manufacturers of lighting equipment publish photometric data for their designs, which shows the quantity and distribution of the light from each lighting fixture. This data is expressed in standardized form.

Modeling

For very simple layouts in common configurations, tables and simple hand calculations can be used. Based on the positions and mounting heights of the fixtures, and their photometric characteristics, the proposed lighting layout can be checked for uniformity and quantity of illumination. For larger projects or those with irregular floor plans, lighting design software can be used. Each fixture has its location entered, and the reflectance of walls, ceiling, and floors can be entered. The computer program will then produce a set of contour charts overlaid on the project floor plan, showing the light level to be expected at the working height. More advanced programs can include the effect of natural light from windows or skylights, allowing further optimization of the operating cost of the lighting installation.

The Zonal Cavity Method is used as a basis for both hand, tabulated, and computer calculations. This method uses the reflectance coefficients of room surfaces to model the contribution to useful illumination at the working level of the room due to light reflected from the walls and the ceiling. Simplified photometric values are usually given by fixture manufacturers for use in this method.

Modelling of ourdoor flood lighting usually proceeds directly from photometric data. The total lighting power of a lamp is divided into small soild angular regions. Each region is extended to the surface which is to be lit and the area calculated, giving the light power per unit of area. Where multiple lamps are used to illuminate the same area, each one's contribution is summed. Again the tablulated light levels (in lux or foot-candles) are presented as contour lines of constant lighting value, overlaid on the project plan drawing. Hand calculations might only be required at a few points, but computer calculations allow a better estimate of the uniformity and lighting level.

Practical lighting design must take into account the gradual decrease in light levels from each lamp owing to lamp aging, lamp burnout, and dirt accumulation on fixture and lamp surfaces. Empirically-established depreciation factors are listed in lighting design handbooks.

Proper selection of fixtures is complicated by the requirement to minimize the veiling reflections off of printed material. Since the exact orientation of printed material may not be closed controlled, a visual comfort probability can be calculated for a given set of lighting fixtures.

Types

Lighting is classified by its intended use as general, localized, or task lighting, depending largely on the distribution of the light produced by the fixture.

Task lighting is mainly functional and is usually the most concentrated, for purposes such as reading or inspection of materials. For example, reading poor-quality reproductions may require task lighting levels up to 1500 lux (150 footcandles), and some inspection tasks or surgical procedures require even higher levels.

Accent lighting is mainly decorative, intended to highlight pictures, plants, or other elements of interior design or landscaping.

General lighting fills in between the two and is intended for general illiumination of an area. Indoors, this would be a basic lamp on a table or floor, or a fixture on the ceiling. Outdoors, general lighting for a parking lot may be as low as 20 lux (2 footcandles) since pedestrians and motorists already used to the dark will need little light for crossing the area.

Methods

Downlighting is most common, with fixtures on the ceiling casting light downward. This tends to be the most efficient method, used in both offices and homes.

Uplighting is less common, often used to bounce indirect light off of the ceiling and back down, though this is less efficient than direct lighting. It can also be used for dramatic effect, such as creating interesting shadows by shining through houseplant leaves or across coarse textures like brick or stone.

Lighting from the front is also quite common, but tends to make the subject look flat as its casts almost no shadows. Lighting from the side is the less common, as it tends to glare near eye level. Backlighting either around or through an object is mainly for accent.

Forms

Particular forms include alcove lighting, which like most other uplighting is indirect. This is often done with fluorescent lighting or rope light, or occasionally with neon lighting. It is a form of backlighting.

Soffit lighting can be general or a decorative wall-wash, sometimes used to bring out texture (like stucco or plaster) on a wall, though this may also show its defects as well. The effect depends heavily on the exact type of lighting used.

Recessed lighting (often called pot lights in Canada and can lights in the U.S.) is popular, with fixtures mounted above the ceiling so as to appear flush with it. These downlights use narrow spotlights or "spots", or wider-angle floodlights or "floods", which are both bulbs with their own reflectors. They may also have their own reflector built-in to the fixture, so that they can take regular and less-expensive bulbs. Either type can be incandescent, fluorescent, HID or LED, though only incandescents or LEDs make narrow-enough spots.

True can lights are uplights, sitting on the floor in a can-like fixture, or mounted on a spike or even in the ground for plants or outdoors.

Track lighting was popular at one point because it was much easier to install then recessed lighting, and individual fixtures are decorative and can be easily aimed at a wall. It has regained some popularity recently in low-voltage tracks, which often look nothing like their predecessors because they do not have the safety issues that line-voltage systems have, and are therefore less bulky and more ornamental in themselves. A master transformer feeds all of the fixtures on the track or rod with 12 or 24 volts, instead of each having its own. There are traditional spots and floods, as well as other small hanging fixtures. A modified version of this is cable lighting, where lights are hung from or clipped to bare metal cables under tension.

The lamp is probably the most common fixture, found in every home and many offices. The standard lamp and shade that sits on a table is general lighting, while the desk lamp is considered task lighting. Magnifier lamps are also task lighting.

The illuminated ceiling was once popular in the 1960s and 1970s but fell out of favor after the 1980s. This uses diffuser panels hung like a suspended ceiling below fluorescent lights, and is considered general lighting.

Other forms include neon, which is not usually intended to illuminate anything else, but to actually be the artwork in itself. This would probably fall under accent lighting, though in a dark nightclub it could be considered general lighting. Underwater accent lighting is also used for koi ponds and the like.

Fixtures

Lighting fixtures come in a wide variety of styles for various functions. Some are very plain and fuctional, while some are pieces of art in themselves. Nearly any material can be used, so long as it can tolerate the heat and is in keeping with safety codes.

A sconce is a wall-mounted fixture, particularly one that shines up and sometimes down as well.

A torchiere (tour-she-AIR or tour-SHARE) is an uplight usually intended for general lighting. It is usually a floor lamp but may be wall-mounted like a sconce. Template:Sect-stub

Bulbs

Light bulbs can be of many types.

Incandescents

The incandescent light bulb was of course first, but it is incredibly inefficient at converting electricity to light. About 90% is wasted as heat, which in summer then has to be cooled out of the air, wasting even more energy. These bulbs can also cause burns and start fires, and tend to have greater glare.

Halogen bulbs are an improved incandescent, being about 15% efficient instead of only 10%, allowing it to put out about 50% more light at the same wattage. The bulb capsule is under high pressure instead of a vacuum however, which in addition to being much smaller and having a hotter filament temperature causes the bulbs to have a very hot surface. This means the glass bulbs can explode if broken, or even if operated with any sort of fingerprints on them. The risk of fire or burn is also greater, leading to their prohibition in dorms and some other places.

Nonetheless, good halogens produce a sunshine-like white light, and regular incandescents produce a light between sunlight and candlelight. Both of these are psycholgically pleasing both in themselves and in the skin tones they bring out, and in the sparkle of their reflection (for small clear bulbs). Halogen capsules can also be put inside regular bulbs or dichroic reflectors for looks or safety.

Fluorescents

Fluorescent bulbs are about 40% efficient, meaning that for the same amount of light they use 1/4 the power and produce 1/6 the heat of a regular incandescent. Fluorescents were limited to linear and a few circular ones until the 1980s, when the compact fluorescent was invented. The compacts can plug into their own fixture, or fit in to a standard screw base for self-ballasted ones. All last far longer than incandescents, but do have some starting trouble in very cold weather when installed outside.

Fluorescents most often come in cool white (CW), with some home bulbs being a warm white (WW), which has a pinkish tint. In between there is an "enhanced white" (EW), which is more neutral. There is also a very cold daylight white (DW) which is rather unpleasant to most people and therefore rarely used. Compact ones are usually considered warm white, though many have a yellowish cast like an incandescent. Because the above terms are entirely relative and almost arbitrary, color temperature and/or the color rendering index (CRI) are used as absolute scales of color for fluorescents, and sometimes for other types of lighting.

HID

High-intensity discharge lighting first came about with the mercury-vapor streetlights, and later the high-pressure sodium ones with their characteristic orange color. Modern ones are metal halide, used in everything from headlights to floodlights, and with a more pleasant color balance. Like fluorescents, all HID bulbs require a ballast, but they also require a few minutes (or seconds for headlights) to warm up after "igniting". HID bulbs are over 60% and up to 80% efficient.

LEDs

LEDs are a very recent introduction to the market, and they are still extremely expensive for any decent-sized bulb. They do however last an extremely long time, up to 100,000 hours (compared to around 10,000 for fluorescent and 1,000 for incandescent). These have come about only since the white LEDs they use, and in turn the blue LEDs which they were based on. It appears that for now these will be most useful and cost-effective in smaller applications, starting with nightlights. Colored LEDs can also be used for accent lighting, even in fake ice cubes for drinks at parties. They are also being increasingly used for Christmas lights, and not just the battery-powered kind. White LEDs are about the same efficiency as other fluorescents, while red ones can be up to 90% efficient.

Vehicle lighting

Automobile Tail Light
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Automobile Tail Light

Vehicles typically include headlights and tail lights. Headlights are white or yellow lights placed in the front of the vehicle, designed to illuminate the upcoming road and to make the vehicle more visible. Tail lights are always red and are placed in the rear to quickly alert other drivers about the vehicle's direction of travel. In the image to the right, the top (white portion) of the tail light is the back-up lamp, which when lit, is used to indicate that the vehicle's transmission has been placed in the reverse gear, warning anyone behind the vehicle that it is moving backwards, or about to do so.

In addition to lighting for useful purposes, automobiles increasingly feature ornamental lighting. In the late 60s and early 70s, manufacturers would sometimes backlight their logos and or other translucent panelling. In the 90s, a popular trend was to customize vehicles with neon lighting, especially underneath the body of a car. In the 2000s, neon lighting is increasingly yielding to digital vehicle lighting, in which bright LEDs are placed on the car and operated by a computer which can be customized and programmed to display a range of changing patterns and colors, a technlogy borrowed from Christmas lights.

See also

Inventors

External links

  • Lighting Design Glossary (http://www.schorsch.com/kbase/glossary/) - Explains the terms used in architectural lighting and lighting simulation, with cross-references to the German language version.
  • http://lightingwiki.com/FrontPage - "a forum for lighting designers, lighting researchers, lighting contractors, and any other people who are interested in illumination related topics, both in architectural and entertainment environments."de:Beleuchtung

eo:Lumigo nl:Verlichtingstechniek ja:照明 pl:Oświetlenie

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