Friday, April 29, 2011

LIGHTING

AR-461: BUILDING SCIENCE
By:
RAVINDAR KUMAR
Assistant Professor
Department of Architecture and Planning
NED University of Engineering and Technology
Karachi
LECTURE NO. 21
TOPIC:                                                              LIGHTING

INTRODUCTION:[1]
Lighting or illumination is the deliberate application of light to achieve some aesthetic or practical effect. Lighting includes use of both artificial light sources such as lamps and natural illumination of interiors from daylight. Day lighting through windows, skylights, etc is often used as the main source of light during daytime in buildings given its high quality and low cost. Artificial lighting represents a major component of energy consumption, accounting for a significant part of all energy consumed worldwide. Artificial lighting is most commonly provided today by electric lights, but gas lighting, candles, or oil lamps were used in the past, and still are used in certain situations. Proper lighting can enhance task performance or aesthetics, while there can be energy wastage and adverse health effects of poorly designed lighting. Indoor lighting is a form of fixture or furnishing, and a key part of interior design. Lighting can also be an intrinsic component of landscaping.
Fig-01: Animated fountain in Moscow's Square of Europe, lit at night (From: http://upload.wikimedia.org/wikipedia/commons/e/e0/Fountain_Europe_Square_Moscow.jpg)

LIGHTING FIXTURES:
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.


Fig-02: A WIDE ARRAY OF LIGHT FIXTURES

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 efficacy but increase the directionality and the visual comfort probability.

LIGHTING TYPES AND CLASSIFICATION:
Lighting is classified by intended use as general, localized, or task lighting, depending largely on the distribution of the light produced by the fixture.

1.  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 foot candles), and some inspection tasks or surgical procedures require even higher levels.
2.   Accent lighting is mainly decorative, intended to highlight pictures, plants, or other elements of interior design or landscaping.
3.   General lighting (sometimes referred to as ambient light) fills in between the two and is intended for general illumination 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 10-20 Luxes (1-2 foot candles) since pedestrians and motorists already used to the dark will need little light for crossing the area.

 
Fig-03: LIGHTING WITHOUT WINDOWS: THE PANTHEON IN THE 18TH CENTURY, PAINTED BY GIOVANNI PAOLO PANINI (From: http://upload.wikimedia.org/wikipedia/commons/6/69/Pantheon-panini.jpg)

LIGHTING METHODS:
There are three common methods of lighting i.e. down lighting, up lighting and front lighting.

1.   Down lighting is most common, with fixtures on or recessed in the ceiling casting light downward. This tends to be the most used method, used in both offices and homes. Although it is easy to design it has dramatic problems with glare and excess energy consumption due to large number of fittings.
2.   Up lighting is less common, often used to bounce indirect light off the ceiling and back down. It is commonly used in lighting applications that require minimal glare and uniform general illuminance levels. Up lighting (indirect) uses a diffuse surface to reflect light in a space and can minimize disabling glare on computer displays and other dark glossy surfaces. It gives a more uniform presentation of the light output in operation.
3.  However indirect lighting is completely reliant upon the reflectance value of the surface. While indirect lighting can create a diffused and shadow free light effect it can be regarded as an uneconomical lighting principle.
4.   Front lighting is also quite common, but tends to make the subject look flat as its casts almost no visible shadows.
5.   Lighting from the side is the less common, as it tends to produce glare near eye level.
6.   Backlighting either around or through an object is mainly for accent.

LIGHTING FORMS:
Lighting is usually observed in two different contexts i.e. in indoor areas and in the outdoors.

INDOOR LIGHTING:
Forms of lighting include alcove lighting, which like most other up lighting is indirect. This is often done with fluorescent lighting (first available at the 1939 World's Fair) or rope light, or occasionally with neon lighting. It is a form of backlighting. Soffit or close to wall 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 source used.

Recessed lighting (often called "pot lights" in Canada, "can lights" or 'high hats" in the US) is popular, with fixtures mounted into the ceiling structure so as to appear flush with it. These down lights can use narrow beam spotlights, or wider-angle floodlights, both of which are bulbs having their own reflectors. There are also down lights with internal reflectors designed to accept common 'A' lamps (light bulbs) which are generally less costly than reflector lamps. Down lights can be incandescent, fluorescent, HID (high intensity discharge) or LED.

Track lighting was popular at one point because it was much easier to install than 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 light fixture having its own line-to-low voltage transformer. 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.

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

A torchiere is an up light intended for ambient lighting. It is typically a floor lamp but may be wall-mounted like a sconce. The portable or table lamp is probably the most common fixture, found in many homes and 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 an artwork in itself. This would probably fall under accent lighting, though in a dark nightclub it could be considered general lighting.

In a movie theater each step in the aisles is usually marked with a row of small lights, for convenience and safety when the film has started, hence the other lights are off. Traditionally made up of small low wattage, low voltage lamps in a track or translucent tube; these are rapidly being replaced with LED based versions.
Fig-04: HIGH MAST LIGHTING ALONG HIGHWAY 401 IN ONTARIO, CANADA

OUTDOOR LIGHTING:

Street Lights are used to light roadways and walkways at night. Some manufacturers are designing LED and photovoltaic luminaires to provide an energy-efficient alternative to traditional street light fixtures.

Floodlights can be used to illuminate outdoor playing fields or work zones during nighttime hours. The most common type of floodlights are metal halide and high pressure sodium lights.

Beacon lights are positioned at the intersection of two roads to aid in navigation.

Security lights can be used along roadways in urban areas, or behind homes or commercial facilities. These are extremely bright lights used to deter crime. Security lights may include floodlights.

Entry lights can be used outside to illuminate and signal the entrance to a property. These lights are installed for safety, security, and for decoration. Underwater accent lighting is also used for koi ponds, fountains, swimming pools and the like. 

Fig-05: A DECORATIVE OUTDOOR LAMP AT LEEDS TOWN HALL

DESIGN AND ARCHITECTURE:
Lighting design as it applies to the built environment, also known as 'architectural lighting design', is both a science and an art. Lighting of structures must consider aesthetic elements as well as practical considerations of quantity of light required, occupants of the structure, energy efficiency and cost. 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.


Fig-06: OLD AND NEW FASIONED BULBS

In some design instances, materials used on walls and furniture play a key role in the lighting effect. Dark paint tends to absorb light, making the room appear smaller and more dim than it is, whereas light paint does the opposite. In addition to paint, reflective surfaces also have an effect on lighting design. Surfaces or floors that are too reflective create unwanted glare.

REFERENCES:

[1] Lighting; From: http://en.wikipedia.org/wiki/Lighting (Retrieved April 29, 2011)
[2] Fig-01: Animated fountain in Moscow's Square of Europe, lit at night (From: http://upload.wikimedia.org/wikipedia/commons/e/e0/Fountain_Europe_Square_Moscow.jpg)
[4] Fig-03: LIGHTING WITHOUT WINDOWS: THE PANTHEON IN THE 18TH CENTURY, PAINTED BY GIOVANNI PAOLO PANINI (From: http://upload.wikimedia.org/wikipedia/commons/6/69/Pantheon-panini.jpg)
[5] Fig-04: HIGH MAST LIGHTING ALONG HIGHWAY 401 IN ONTARIO, CANADA (From: http://upload.wikimedia.org/wikipedia/commons/b/b1/Highway_401_Night_Lapse_Busy.jpg)

1 comment: