Title: Reading and Audio-Visual Assignments
Course: WGF 107 DEVELOPMENT > Section: Content

Image | General Electric's "foot candle" advertising novelty

Sub-Title | Key Measurements Involving Light – Lumens & Foot-candles
Content
If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, the total luminous flux emitted into that angle is one lumen (1 cd·1 sr = 1 lm). Alternatively, an isotropic one-candela light-source emits a total luminous flux of exactly 4π lumens. If the source were partially covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens. The luminous intensity would still be one candela in those directions that are not obscured.

The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.

The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m^2.

A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.

Lighting[edit]

See also: LED lampand Incandescent light bulb

Lamps used for lighting are commonly labeled with their light output in lumens; in many jurisdictions this is required by law.

A 23 watt compact fluorescent lamp emits about 1,500–1,600 lm.^[3]^[4]

On September 1, 2010, European Union legislation came into force mandating that lighting equipment must be labelled primarily in terms of lumens, instead of watts of electric power consumed.^[5] This change is a result of the EU's Eco-design Directive for Energy-using Products (EuP).^[6] For example, according to the European Union standard, an energy-efficient bulb that claims to be the equivalent of a 60 W tungsten bulb must have a minimum light output of 700-750 lumens.^[7]

To estimate lumens from watts for various types of lamp, see luminous efficacy.

Lighting or illumination is the deliberate use of light to achieve a practical or aesthetic effect. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting (using windows, skylights, or light shelves) is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.

Indoor lighting is usually accomplished using light fixtures, and is a key part of interior design. Lighting can also be an intrinsic component of landscape projects.
Image | Low-intensity lighting and haze in a concert hall allows laser effects to be visible
Content | A foot-candle (sometimes foot candle; abbreviated fc, lm/ft^2, or sometimes ft-c) is a non-SI unit of illuminance or light intensity widely used^[^citation needed^] in the United States in photography, film, television, conservation lighting, the lighting industry, construction-related engineering and in building codes. The name "footcandle" conveys "the illuminance cast on a surface by a one-candela source one foot away". As natural as this sounds, this style of name is now frowned upon, because dimensionally illuminance is not length times luminous intensity as the name would imply but instead luminous intensity per unit area. The unit is defined as the amount of illumination the inside surface of a one-foot-radius sphere would be receiving if there were a uniform point source of one candela in the exact center of the sphere. Alternatively, it can be defined as the illuminance on a one-square foot surface of which there is a uniformly distributed flux of one lumen. Thus one foot-candle is equal to one lumen per square foot or approximately 10.764 lux.^[note 2] In practical applications, as when measuring room illumination, it is very difficult to measure illuminance more accurately than ±10%, and for many purposes it is quite sufficient to think of one footcandle as about ten lux as is typically done in the lighting industry.
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Wikipedia

Lumens                                    http://en.wikipedia.org/wiki/Lumens

Foot-candles                                http://en.wikipedia.org/wiki/Foot-candle

Lighting                                   http://en.wikipedia.org/wiki/Lighting

Diffuse Reflection     http://en.wikipedia.org/wiki/Diffuse_reflection

Light Reflectance Value http://en.wikipedia.org/wiki/Light_Reflectance_Value

Light Specular Value http://en.wikipedia.org/wiki/Specular_reflection

Energy-saving Lighting – Energy Efficiency and Renewable Energy                                                      http://energy.gov/public-services/homes/saving-electricity/lighting
Attributions | Image and Content courtesy of Wikipedia – The Free Internet Encyclopedia