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Lighting - Lighting design

Lighting - Lighting design: Encyclopedia II - Lighting - Lighting design

Lighting: Encyclopedia II - Lighting - Lighting design

Lighting - Lighting design

Lighting design as it applies to the built environment, also known as 'architectural lighting design', is both a science and an art. Proper comprehensive lighting design requires consideration of the amount of functional light provided, the energy consumed, 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 artificial light production and luminaire photometrics are balanced with the artistic application of light as a medium in our built environment. These artificial lighting systems should also consider the impacts of, and ideally be integrated with, daylighting systems.

Lighting design requires the consideration of several design factors:

tasks occurring in the environment
occupants of the environment
initial and continued operational costs
aesthetic architectural impact
physical size of the environment
surface characteristics (reflectance, specularity)
dirt and dust generation/accumulation
maintenance capabilities
operating schedule of the building
electrical codes and building codes

The Illuminating Engineering Society of North America (IESNA), in conjunction with organizations like ANSI and ASHRAE, publishes guidelines, standards, and handbooks that allow categorization of the illumination needs of different built environments. Manufacturers of lighting equipment publish photometric data for their products, which defines the distribution of light released by a specific luminaire. This data is typically expressed in standardized form defined by the IESNA.

The International Association of Lighting Designers (IALD) is an organization which focuses on the advancement of lighting design education and the recognition of independent professional lighting designers. Those fully independent designers who meet the requirements for professional membership in the association typically append the abbreviation IALD to their name.

The National Council on Qualifications for the Lighting Professions (NCQLP) offers the Lighting Certification Examination which tests rudimentary lighting design principles. Individuals who pass this exam become ‘Lighting Certified’ and may append the abbreviation LC to their name. This certification process is the only national examination in the lighting industry and is open not only to designers, but to lighting equipment manufacturers, electric utility employees, etc.

Lighting - 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 outdoor 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 tabulated 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.

Lighting - 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.

Lighting - 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.

Lighting - 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, invented by Lightolier, 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.