Architectural lighting design

See also: Lighting
Play of light inside Jatiyo Sangshad Bhaban

Architectural lighting design is a field within architecture, interior design and electrical engineering that is concerned with the design of lighting systems, including natural light, electric light, or both, to serve human needs.[1]

The design process takes account of:

It is important to appreciate that the ultimate criterion of success in lighting is the human response, that is. whether what is to be seen clearly, easily and without discomfort."[1] Lighting designers are often specialists who must understand the physics of light production and distribution, the physiology and psychology of light perception by humans, the anatomy of the human eye, and the response of the rods and cones to light.

History

With the discovery of fire, the earliest form of artificial lighting used to illuminate an area were campfires or torches. As early as 400,000 BCE, fire was kindled in the caves of Peking Man. Prehistoric people used primitive lamps to illuminate surroundings. These lamps were made from naturally occurring materials such as rocks, shells, horns and stones, were filled with grease, and had a fiber wick. Lamps typically used animal or vegetable fats as fuel. Hundreds of these lamps (hollow worked stones) have been found in the Lascaux caves in modern-day France, dating to about 15,000 years ago. Oily animals (birds and fish) were also used as lamps after being threaded with a wick. Fireflies have been used as lighting sources. Candles and glass and pottery lamps were also invented.[2] Chandeliers were an early form of "light fixture".

Major reductions in the cost of lighting occurred with the discovery of whale oil and kerosene.[3] The potential of electric light as a new building material was recognized in the 1920s and became a useful design tool by the mid-century. Skillful lighting allowed for theatricality, narrative, and a new emphasis on structure and space

Gas lighting was economical enough to power street lights in major cities starting in the early 1800s, and was also used in some commercial buildings and in the homes of wealthy people. The gas mantle boosted the luminosity of utility lighting and of kerosene lanterns. The next major drop in price came about with the incandescent light bulb powered by electricity.[3]

Over time, electric lighting became ubiquitous in developed countries. Segmented sleep patterns disappeared, improved nighttime lighting made people made more activities possible at night, and more street lights reduced urban crime.Without light fittings there can be no Architectural Lighting Design. As these light sources change so does the practice of lighting Design.

Candles

Main article: Candle

For most of recorded history candles were tallow and beeswax until the mid 1800s at which point they were made mainly from spermaceti (spurring larger demand for whale oil), and purified animal fats (stearin) ox fat, rat fat and even pigeon fat when sailors were at sea. The Whaling industry was based around acquiring the whale oil to create candles and light.

A candle manufacturer is traditionally known as a chandler.[4] Various devices have been invented to hold candles, from simple tabletop candle holders, to elaborate chandeliers.

Argand lamps

Main article: Argand lamp
An Argand lamp in use
Argand lamp with circular wick and glass chimney (illustration from Les Merveilles de la science [1867-1869] by Louis Figuier)

The Argand lamp is a home lighting oil lamp producing a light output of 6 to 10 candela which was invented and patented in 1780 by Aimé Argand. Aside from the improvement in brightness, the more complete combustion of the wick and oil required much less frequent trimming of the wick.

In France, they are known as "Quinquets" after Antoine-Arnoult Quinquet, a pharmacist in Paris, who used the idea originated by Argand and popularized it in France. He is sometimes credited with the addition of the glass chimney to the lamp.[5]

It was the lamp of choice until about 1850 when kerosene lamps were introduced.

Kerosene lamps

Main article: Kerosene lamp

A kerosene lamp or paraffin lamp is a type of lighting device that uses kerosene as a fuel. Kerosene lamps have a wick or mantle as light source, protected by a glass chimney or globe; lamps may be used on a table, or hand-held lanterns may be used for portable lighting.

Kerosene was cheaper than vegetable oil, it produced a whiter flame, and as a liquid of low viscosity it could easily travel up a wick eliminating the need for complicated mechanisms to feed the fuel to the burner.

The first description of a simple lamp using crude mineral oil, the predecessor of the kerosene lamp, was provided by al-Razi (Rhazes) in 9th century Baghdad, who referred to it as the "naffatah" in his Kitab al-Asrar (Book of Secrets). In 1846, Abraham Pineo Gesner pioneered the use of kerosene distilled from coal a substitute for whale oil for lighting. Later made from petroleum, kerosene became a popular lighting fuel. Modern versions of the kerosene lamp were later constructed by the Polish inventor Ignacy Łukasiewicz in 1853 Lemberg.

Gas lighting

Main article: Gas lighting

Before electricity became sufficiently widespread and economical to allow for general public use, gas was the most popular means of outdoor and indoor lighting in cities and suburbs. Early gas lights had to be lit manually, but many later designs are self-igniting. It must be remembered that the last gas lighting workers finished in London during the 1950s. Gas lighting competed with the development of electric light for many years. In addition, some urban historical districts retain gas street lighting, and gas lighting is used indoors or outdoors to create or preserve a nostalgic effect as well as a status symbol among the elite.

Among the economic impacts of gas lighting, was much longer work hours in factories. This was particularly important in Great Britain during the winter months when nights are significantly longer. Factories could even work continuously over 24 hours, resulting in increased production. Following successful commercialization, gas lighting spread to other countries.

Early lighting fuels consisted of olive oil, beeswax, fish oil, whale oil, sesame oil, nut oil, and similar substances. These were the most commonly used fuels until the late 18th century.

Solar reflectors

Adjustable light reflector

Once used extensively in office buildings, the adjustable light reflector is seldom in use today having been supplanted by a combination of other methods in concert with artificial illumination. The reflector had found favor where the choices of artificial light provided poor illumination compared to modern electric lighting.

Electric lighting

Main article: Electric light

Architectural lighting design coincides with the rapid development of cities and electric light to achieve what was coined at the turn of the century as "nocturnal modernity". The image of a New York City night scape with electric light spurned the imagination. The potential of electric light as a new building “material” was recognized in the 1920s and became a useful design tool by the mid-century. Skillful lighting allowed for theatricality, narrative, and a new emphasis on structure and space. These ideas of using at the time new light source of electricity and mass-produced glass walls for daylighting were first experimented with by Josef Hoffmann of the Vienna Secession and Wiener Werkstätte, Walter Gropius' art school, known as Bauhaus of 1919 and Russian state art and technical school in Moscow, known as Higher Art and Technical Studios and abbreviated simply as Vkhutemas.

With the exodus from Europe after the second world war the Bahaus brought its modern ideas to the United States. Mies van der Rohe and Walter Gropius ideas were brought to America and quickly taken up by architects such as Phillip Johnson in the conceptual Glass House a supreme example of the use of daylighting and natural light. They both used the lighting designer Richard Kelly who was one of the field’s most influential figure in developing Lighting design as a professional in the United States. One of the oldest architectural lighting manufacturers in the world today is run by the fourth generation of the Baldinger family, Howard Baldinger of HB Architectural Lighting( http://www.hblightinginc.com/ ). Started in 1893 in Pennsylvania, the Baldinger family created a name for themselves by their continuous execution of high quality manufacturing of architectural lighting. They produced lighting design by some of the most famous designers of the twentieth century. Their high quality craftsmanship continues to this day with some of the most highly regarded institutions among the Hospitality Industry, among others.

Fluorescent lighting

Main article: Fluorescent lamp

A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The luminous efficacy of a fluorescent light bulb can exceed 100 lumens per watt, several times the efficacy of an incandescent bulb with comparable light output.

Concept

Auditorium of the Viipuri Municipal Library in the 1930s

Extensive luminaire photometric designing calls for consideration of the amount of functional light present, the energy expended, as well as the aesthetic impact supplied by the lighting system. Some buildings, like surgical centers and sports facilities, are primarily concerned with providing the appropriate amount of light for the associated task. Some buildings, like warehouses and office buildings, are primarily concerned with saving money through the energy efficiency of the lighting system. Other buildings, like casinos and theatres, are primarily concerned with enhancing the appearance and emotional impact of architecture through lighting systems. Therefore, it is important that the sciences of light production and luminaire photometrics are balanced with the artistic application of light as a medium in our built environment. These electrical lighting systems should also consider the impacts of, and ideally be integrated with, daylighting systems. Factors involved in lighting design are essentially the same as those discussed above in energy conservation analysis.

Architectural lighting design focuses on three fundamental aspects of the illumination of buildings or spaces. The first is the aesthetic appeal of a building, an aspect particularly important in the illumination of retail environments. Secondly, the ergonomic aspect: the measure of how much of a function the lighting plays. Thirdly is the energy efficiency issue to ensure that light is not wasted by over-illumination, either by illuminating vacant spaces unnecessarily or by providing more light than needed for the aesthetics or the task.

Each of these three aspects is looked at in considerable detail when the lighting designer is at work. In aesthetic appeal, the lighting designer attempts to raise the general attractiveness of the design, measure whether it should be subtly blended into the background or whether it should stand out, and assess what kind of emotions the lighting should evoke. The functional aspects of the project can encompass the need for the project to be visible (by night mostly, but also by day), the impact of daylight on the project and safety issues (glare, colour confusion etc.).

Day lighting

As the Sun crosses the sky, it may appear to be red, orange, yellow or white depending on its position. The changing color of the Sun over the course of the day is mainly a result of scattering of light and is not due to changes in black-body radiation. The blue color of the sky is caused by Rayleigh scattering of the sunlight from the atmosphere, which tends to scatter blue light more than red light.

Daylight has a spectrum similar to that of a black body with a correlated color temperature of 6,500 K (D65 viewing standard) or 5,500 K (daylight-balanced photographic film standard).

For colors based on black-body theory, blue occurs at higher temperatures, while red occurs at lower, cooler, temperatures. This is the opposite of the cultural associations attributed to colors, in which "red" is "hot", and "blue" is "cold".[6]

Fixtures

Main article: Light fixture
The PH5 lamp, designed in 1958

Lighting fixtures come in a wide variety of styles for various functions. The most important functions are as a holder for the light source, to provide directed light and to avoid visual glare. Some are very plain and functional, while some are pieces of art in themselves. Nearly any material can be used, so long as it can tolerate the excess heat and is in keeping with safety codes.

An important property of light fixtures is the luminous efficacy or wall-plug efficiency, meaning the amount of usable light emanating from the fixture per used energy, usually measured in lumen per watt. A fixture using replaceable light sources can also have its efficiency quoted as the percentage of light passed from the "bulb" to the surroundings. The more transparent the lighting fixture is, the higher efficacy. Shading the light will normally decrease efficiency but increase the directionality and the visual comfort probability.

Photometric studies

The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures (Planckian locus), and lines of constant correlated color temperature

Photometric studies (also sometimes referred to as "layouts" or "point by points") are often used to simulate lighting designs for projects before they are built or renovated. This enables architects, lighting designers, and engineers to determine whether a proposed lighting setup will deliver the amount of light intended. They will also be able to determine the contrast ratio between light and dark areas. In many cases these studies are referenced against IESNA or CIBSE recommended lighting practices for the type of application. Depending on the type of area, different design aspects may be emphasized for safety or practicality (i.e. such as maintaining uniform light levels, avoiding glare or highlighting certain areas). Specialized software is often used to create these, which typically combine the use of two-dimensional digital CAD drawings and lighting calculation software (i.e. AGi32or Dialux).

Color temperature for white light sources also affects their use for certain applications. The color temperature of a white light source is the temperature in Kelvin of a theoretical black body emitter that most closely matches the spectral characteristics of the lamp. An incandescent bulb has a color temperature around 2800 to 3000 Kelvin; daylight is around 6400 Kelvin. Lower color temperature lamps have relatively more energy in the yellow and red part of the visible spectrum, while high color temperatures correspond to lamps with more of a blue-white appearance. For critical inspection or color matching tasks, or for retail displays of food and clothing, the color temperature of the lamps will be selected for the best overall lighting effect.

The PH-lamps are a series of light fixtures designed by Danish designer and writer Poul Henningsen from 1926 onwards.[7] The lamp is designed with multiple concentric shades to eliminate visual glare, only emitting reflected light, obscuring the light source.[8] The lamps are still in production today.

Correlated color temperature

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other fields. In practice, color temperature is only meaningful for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e., those on a line from reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of the color temperature of, e.g., a green or a purple light. Color temperature is conventionally stated in the unit of absolute temperature, the Kelvin, having the unit symbol K.

For lighting building interiors, it is often important to take into account the color temperature of illumination. For example, a warmer (i.e., lower color temperature) light is often used in public areas to promote relaxation, while a cooler (higher color temperature) light is used to enhance concentration in offices.[9]

CCT dimming for LED technology is regarded as a difficult task, since binning, age and temperature drift effects of LEDs change the actual color value output. Here feedback loop systems are used for example with color sensors, to actively monitor and control the color output of multiple color mixing LEDs.[10]

The color temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in Kelvin, or alternatively in mireds (micro-reciprocal Kelvin).[11] This permits the definition of a standard by which light sources are compared.

Categorizing different lighting

Temperature Source
1,700 K Match flame, low-pressure sodium lamps (LPS/SOX)
1,850 K Candle flame, sunrise, sunset
2,700–3,300 K Incandescent lamps, soft-white fluorescent lamps
3,000 K Warm-white fluorescent lamps
4,100–4,150 K Moonlight,[12] cool-white fluorescent lamps
5,000 K Horizon daylight
5,500–6,000 K Vertical daylight, electronic flash
6,200 K Xenon short-arc lamp[13]
6,500 K Daylight, overcast, daylight fluorescent lamps
6,500–10,500 K LCD or CRT screen
15,000–27,000 K Clear blue poleward sky
These temperatures are merely characteristic;
considerable variation may be present.

To the extent that a hot surface emits thermal radiation but is not an ideal black-body radiator, the color temperature of the light is not the actual temperature of the surface. An incandescent lamp's light is thermal radiation, and the bulb approximates an ideal black-body radiator, so its color temperature is essentially the temperature of the filament.

Many other light sources, such as fluorescent lamps, or LEDs (light emitting diodes) emit light primarily by processes other than thermal radiation. This means that the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black-body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from the comparison to a black-body radiator.

Methods

For simple installations, hand-calculations based on tabular data can be used to provide an acceptable lighting design. More critical or optimized designs now routinely use mathematical modeling on a computer.

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 light from windows or skylights, allowing further optimization of the operating cost of the lighting installation. The amount of daylight received in an internal space can typically be analyzed by undertaking a daylight factor calculation.

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.

Computer modeling of outdoor flood lighting usually proceeds directly from photometric data. The total lighting power of a lamp is divided into small solid 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 tabulated light levels (in lux or foot-candles) can be 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.

International professional organisations

The Illuminating Engineering Society of Australia and New Zealand was established in 1930 during the Great Depression.

The International Association of Lighting Designers (IALD) was founded in 1969, and its current mission is "to serve the IALD worldwide membership by promoting the visible success of its members in practicing lighting design." The organization created a new attitude towards the profession and raised the profile of architectural lighting design, one its principal goals.

The European Lighting Designers' Association (ELDA, later ELDA+) was formed in 1993; in 2007, ELDA changed its name to the Professional Lighting Designers Association (PLDA). The IALD and PLDA are the main authorities regarding lighting design in architecture.

The Illuminating Engineering Society of North America (IESNA) seeks to improve the lighted environment by bringing together those with lighting knowledge and by translating that knowledge into actions that benefit the public.

The National Council on Qualifications for the Lighting Professions (NCQLP) is a non-profit organization founded in 1991 to serve and protect the well-being of the public through effective and efficient lighting practice. Through a peer-review process, the NCQLP establishes the education, experience and examination requirements for baseline certification across the lighting professions. The NCQLP has established a certification process by which practitioners in lighting and related fields, through testing, demonstrate their knowledge and experience across the lighting professions. Those who successfully complete the NCQLP Lighting Certification Examination are entitled to use the appellation LC (Lighting Certified) after their name for professional purposes.

The International Commission on Illumination (CIE) is an organization "devoted to international cooperation and exchange of information among its member countries on all matters relating to the science and art of lighting." CIE works globally to develop and publish lighting design standardization and best-practice documents.

The Professional Lighting & Sound Association (PLASA) represents the interests of many lighting designers and manufacturers, several of which are involved in the Architectural lighting market. PLASA is UK orientated, but does represent companies on a European and International level.

There are many more nationally-based organizations such as the Schweizerische Licht Gesellschaft (SLG) in Switzerland, the Association des Concepteurs Lumière et Éclairagistes (ACE) in France, the Hellenic Illumination Committee (HIC) in Greece and the Associazione Professionisti dell'Illuminazione (APIL) in Italy.

Iconic designs

Villa Savoye
Kimbell Art Museum, Fort Worth, Texas (1966–72)
30 St Mary Axe from Leadenhall Street

Notable designers

Decorative Luminare designers

Light-fixture controls

Publications on architectural lighting design

Illuminated Cherry blossoms, light from the shop windows, and Japanese lantern at night in Ise, Mie, Japan

Architectural design media

With the increase in global focus on green design and energy codes, lighting design and its role in sustainability have become more well known, resulting in a number of lighting-specific trade publications and an increase in coverage in architectural publications.

The following are publications specific to lighting design, covering the global-nature of the industry:

Terminology

Recessed light 
The protective housing is concealed behind a ceiling or wall, leaving only the fixture itself exposed. The ceiling-mounted version is often called a downlight.
"Cans" with a variety of lamps 
Jargon for inexpensive downlighting products that are recessed into the ceiling, or sometimes for uplights placed on the floor. The name comes from the shape of the housing. The term "pot lights" is often used in Canada and parts of the US.
Cove light 
Recessed into the ceiling in a long box against a wall.
Floor lamp
Troffer 
Recessed fluorescent light fixtures, usually rectangular in shape to fit into a drop ceiling grid.
Surface-mounted light 
The finished housing is exposed, not flush mount with surface
Chandelier
Pendant light 
Suspended from the ceiling with a chain or pipe
Sconce 
Provide up or down lights; can be used to illuminate artwork, architectural details; commonly used in hallways or as an alternative to overhead lighting.
Track lighting fixture 
Individual fixtures ("track heads") can be positioned anywhere along the track, which provides electric power.
Under-cabinet light 
Mounted below kitchen wall cabinets
Emergency lighting or exit sign 
Connected to a battery backup or to an electric circuit that has emergency power if the mains power fails
High- and low-bay lighting 
Typically used for general lighting for industrial buildings and often big-box stores
Strip lights or Industrial lighting 
Often long lines of fluorescent lamps used in a warehouse or factory
Outdoor lighting and landscape lighting 
Used to illuminate walkways, parking lots, roadways, building exteriors and architectural details, gardens, and parks.
Bollard 
A type of architectural outdoor lighting that is a short, upright ground-mounted unit typically used to provide cutoff type illumination for egress lighting, to light walkways, steps, or other pathways.
Street light
Flood lighting 
Usually pole- or stanchion-mounted — for landscape, roadways, and parking lots

Lamp types

Types of electric lighting include:

Different types of lights have vastly differing efficiencies and color of light.

Name Optical spectrum Nominal efficiency
(lm/W) 		Lifetime (MTTF)
(hours) 		Color temperature
(kelvin) 		Color Color
rendering
index
Incandescent light bulb Continuous 4-17 2-20000 2400-3400 Warm white (yellowish) 100
Halogen lamp Continuous 16-23 3000-6000 3200 Warm white (yellowish) 100
Fluorescent lamp Mercury line + Phosphor 52-100 (white) 8000-20000 2700-5000* White (various color temperatures), as well as saturated colors available 15-85
Metal halide lamp Quasi-continuous 50-115 6000-20000 3000-4500 Cold white 65-93
Sulfur lamp Continuous 80-110 15000-20000 6000 Pale green 79
High pressure sodium Broadband 55-140 10000-40000 1800-2200* Pinkish orange 0-70
Low pressure sodium Narrow line 100-200 18000-20000 1800* Yellow, no color rendering 0
Light-emitting diode Line plus phosphor 10-110 (white) 50,000-100,000 Various white from 2700 to 6000* Various color temperatures, as well as saturated colors 70-85 (white)
Induction Lamp (External Coil) Mercury line + Phosphor 70-90 (white) 80,000-100,000 Various white from 2700 to 6000* Various color temperatures, as well as saturated colors 70-85 (white)

*Color temperature is defined as the temperature of a black body emitting a similar spectrum; these spectra are quite different from those of black bodies.

The most efficient source of electric light is the low-pressure sodium lamp. It produces, for all practical purposes, a monochromatic orange/yellow light, which gives a similarly monochromatic perceprtion of any illuminated scene. For this reason, it is generally reserved for outdoor public lighting usages. Low-pressure sodium lights are favoured for public lighting by astronomers, since the light pollution that they generate can be easily filtered, contrary to broadband or continuous spectra.

Incandescent light bulb

The modern incandescent lightbulb, with a coiled filament of tungsten, was commercialized in the 1920s developed from the carbon filament lamp introduced in about 1880. As well as bulbs for normal illumination, there is a very wide range, including low voltage, low-power types often used as components in equipment, but now largely displaced by LEDs

There is currently interest in banning some types of filament lamp in some countries, such as Australia planning to ban standard incandescent light bulbs by 2010, because they are inefficient at converting electricity to light. Sri Lanka has already banned importing filament bulbs because of high use of electricity and less light. Less than 3% of the input energy is converted into usable light. Nearly all of the input energy ends up as heat that, in warm climates, must then be removed from the building by ventilation or air conditioning, often resulting in more energy consumption. In colder climates where heating and lighting is required during the cold and dark winter months, the heat byproduct has at least some value.

Halogen lamp

Main article: Halogen lamp

Halogen lamps are usually much smaller than standard incandescents, because for successful operation a bulb temperature over 200 °C is generally necessary. For this reason, most have a bulb of fused silica (quartz), but sometimes aluminosilicate glass. This is often sealed inside an additional layer of glass. The outer glass is a safety precaution, reducing UV emission and because halogen bulbs can occasionally explode during operation. One reason is if the quartz bulb has oily residue from fingerprints. The risk of burns or fire is also greater with bare bulbs, leading to their prohibition in some places unless enclosed by the luminaire.

Those designed for 12 V or 24 V operation have compact filaments, useful for good optical control, also they have higher efficiencies (lumens per watt) and better lives than non halogen types. The light output remains almost constant throughout life.

Fluorescent lamp

Main article: Fluorescent lamp

Fluorescent lamps consist of a glass tube that contains mercury vapour or argon under low pressure. Electricity flowing through the tube causes the gases to give off ultraviolet energy. The inside of the tubes are coated with phosphors that give off visible light when struck by ultraviolet energy.[15] have much higher efficiency than Incandescent lamps. For the same amount of light generated, they typically use around one-quarter to one-third the power of an incandescent.

LED lamp

Main article: Solid-state lighting

Solid state LEDs have been popular as indicator lights since the 1970s. In recent years, efficacy and output have risen to the point where LEDs are now being used in niche lighting applications.

Indicator LEDs are known for their extremely long life, up to 100,000 hours, but lighting LEDs are operated much less conservatively (due to high LED cost per watt), and consequently have much shorter lives.

Due to the relatively high cost per watt, LED lighting is most useful at very low powers, typically for lamp assemblies of under 10 W. LEDs are currently most useful and cost-effective in low power applications, such as nightlights and flashlights. Colored LEDs can also be used for accent lighting, such as for glass objects, and even in fake ice cubes for drinks at parties. They are also being increasingly used as holiday lighting.

LED efficiencies vary over a very wide range. Some have lower efficiency than filament lamps, and some significantly higher. LED performance in this respect is prone to being misinterpreted, as the inherent directionality of LEDs gives them a much higher light intensity in one direction per given total light output.

Single color LEDs are well developed technology, but white LEDs at time of writing still have some unresolved issues:

LED technology is useful for lighting designers because of its low power consumption, low heat generation, instantaneous on-and-off control, and in the case of single color LEDs, continuity of color throughout the life of the diode and relatively low cost of manufacture.

In the last few years, software has been developed to merge lighting and video by enabling lighting designers to stream video content to their LED fixtures, creating low resolution video walls.

For general domestic lighting, total cost of ownership of LED lighting is still much higher than for other well established lighting types.

Carbon arc lamp

Main article: Arc lamp

Carbon arc lamps consist of two carbon rod electrodes in open air, supplied by a current-limiting ballast. The electric arc is struck by touching the rods then separating them. The ensuing arc heats the carbon tips to white heat. These lamps have higher efficiency than filament lamps, but the carbon rods are short lived and require constant adjustment in use. The lamps produce significant ultra-violet output, they require ventilation when used indoors, and due to their intensity they need protecting from direct sight.

Invented by Humphry Davy around 1805, the carbon arc was the first practical electric light. They were used commercially beginning in the 1870s for large building and street lighting until they were superseded in the early 20th century by the incandescent light. Carbon arc lamps operate at high powers and produce high intensity white light. They also are a point source of light. They remained in use in limited applications that required these properties, such as movie projectors, stage lighting, and searchlights, until after World War 2.

Discharge lamp

A discharge lamp has a glass or silica envelope containing two metal electrodes separated by a gas. Gases used include, neon, argon, xenon, sodium, metal halide, and mercury.

The core operating principle is much the same as the carbon arc lamp, but the term 'arc lamp' is normally used to refer to carbon arc lamps, with more modern types of gas discharge lamp normally called discharge lamps.

With some discharge lamps, very high voltage is used to strike the arc. This requires an electrical circuit called an igniter, which is part of the ballast circuitry. After the arc is struck, the internal resistance of the lamp drops to a low level, and the ballast limits the current to the operating current. Without a ballast, excess current would flow, causing rapid destruction of the lamp.

Some lamp types contain a little neon, which permits striking at normal running voltage, with no external ignition circuitry. Low pressure sodium lamps operate this way.

The simplest ballasts are just an inductor, and are chosen where cost is the deciding factor, such as street lighting. More advanced electronic ballasts may be designed to maintain constant light output over the life of the lamp, may drive the lamp with a square wave to maintain completely flicker-free output, and shut down in the event of certain faults.

See also

References

  1. 1 2 Lighting : basic concepts / Warren G. Julian, editor ; written by members of the Architectural Science Dept, University of Sydney
  2. ↑ Williams, Ben (1999). "A History of Light and Lighting". Retrieved 23 November 2012.
  3. 1 2 http://www.npr.org/blogs/money/2014/04/25/306862378/episode-534-the-history-of-light
  4. ↑ "Chandler". The Free Dictionary By Farlex. Retrieved 2012-05-19.
  5. ↑ "Lamp." Columbia Electronic Encyclopedia, 6Th Edition (2011): 1. Academic Search Premier. Web. 5 Dec. 2011.
  6. ↑ Chris George (2008). Mastering Digital Flash Photography: The Complete Reference Guide. Sterling Publishing Company. p. 11. ISBN 978-1-60059-209-6.
  7. ↑ "The PH lamp", Design, Visit Denmark.
  8. ↑ "Poul Henningsen", Designers, Louis Poulsen Lighting.
  9. ↑ Rüdiger Paschotta (2008). Encyclopedia of Laser Physics and Technology. Wiley-VCH. p. 219. ISBN 978-3-527-40828-3.
  10. ↑ Thomas Nimz, Fredrik Hailer and Kevin Jensen (2012). Sensors and Feedback Control of Multi-Color LED Systems. LED Professional. pp. 2–5. ISSN 1993-890X.
  11. ↑ Wallace Roberts Stevens (1951). Principles of Lighting. Constable.
  12. ↑ Parrott, Steve. "Moonlighting: Landscape Lighting Design Imitates Nature". Retrieved 2011-09-29.
  13. ↑ "OSRAM SYVLANIA XBO" (PDF).
  14. ↑ Watkin, David (1996). The History of Western Architecture (Second ed.). Laurence King Publishing. pp. 508–509. ISBN 1-85669-082-2.
  15. ↑ Perkowitz, Sidney; Henry, A. Joseph (23 November 1998). Empire of Light:: A History of Discovery in Science and Art. Joseph Henry Press. ISBN 978-0309065566. Retrieved 4 November 2014.

External links

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