| Key-word |
Unit |
Definition |
|
| altitude |
|
The vertical angular distance of a point in the sky above the horizon. Altitude is measured positively from the horizon to the zenith, from 0 to 90 degrees. |
|
| ambient light |
|
Electric and/or natural lighting throughout a space that produces uniform general illumination. |
|
| azimuth |
|
The horizontal angular distance between the vertical plane containing a point in the sky and true south. |
|
| candela |
cd (candela) |
The power of a light source: the luminous intensity or the flow of light in a given direction, where 1 cd = 1 lm/sr. |
|
| candela per sqm |
cd/mē (candela/sqm) |
Also known as 'brightness', a measure of the flux emitted from, or reflected by, a relatively flat and uniform surface. Is also the luminous intensity per unit area. |
|
| CEI |
|
Commission Internationale de l'Eclairage |
|
| clear sky |
|
Sunny weather, no clouds, full sunlight. |
|
| color temperature |
|
The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source (see correlated color temperature). |
|
| contrast |
|
The ratio of the luminance of an object to that of its immediate background. |
|
| daylight saving time |
|
The practice of advancing the clock one hour in the spring of the year. Meant as a source of energy savings through better use of free daylight. |
|
| daylightfactor (DF) |
|
The daylightfactor is computed by dividing the amount of indoor illuminance at a point on a workplane by the outdoor illuminance under overcast conditions. |
|
| diffuse light |
|
Light scattered in all directions. |
|
| disability glare |
|
Glare resulting in reduced visual performance and visibility. Often accompanied by discomfort glare |
|
| discomfort glare |
|
Glare producing discomfort. |
|
| false color |
|
A technique scientists use to help them see details in images of objects. The colors the scientist picks for his or her image may have nothing to do with the color of the object. In the case of LightTool, the chosen colors represent the luminance or illuminance values. The term "false color" does not mean that the data are wrong or that the picture is deceiving you. It only means that the figure is not a color photograph. You should look at the scale or legend to interpret it. |
|
| g-value |
|
Also called 'solar heat gain factor': the measure of how much solar energy is finally let in. Expressed as a percentage or fraction. |
|
| glare |
|
See disability glare, discomfort glare. |
|
| glare index |
|
A method of predicting the presence of discomfort glare due to daylighting. Factors affecting the glare index include the size and relative position of fenestration, sky luminance, and interior luminance. Most widely used in Europe, the glare index is similar to the index of sensation and the discomfort glare rating, which are used in North America for electric lighting applications. |
|
| human sensitive |
|
As the human eye perceives it. |
|
| illuminance |
lx (lux) |
Unit of illumination, equal to one lumen per m? or to the illumination of a surface uniformly one meter distant from a point source of one candle. |
|
| light |
|
Radiant energy that is capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum (light) extends from about 0.38 to 0.77 microns (380 to 770 nm). |
|
| lumen of flow of light |
lm (lumen) |
Unit of the flow of light, equal to the amount of flow through a unit solid angle from a uniform point source of one candle. |
|
| luminance |
cd/m? (candela/sqm) |
Also known as 'brightness', a measure of the flux emitted from, or reflected by, a relatively flat and uniform surface. Is also the luminous intensity per unit area. |
|
| luminance ratio |
% |
Ratio between the light reflected off an object and that reflected off the background against which the object is seen. Usually, a maximum ratio of 1/10 is necessary for visual comfort, while often a ratio of 1/3 is recommended. With a typical luminance value for a computer display unit of 100 cd/m?, the luminance value behind the shading system should be lower than 1000 cd/m?. |
|
| luminous flux |
lm (lumen) |
Unit of the flow of light, equal to the amount of flow through a unit solid angle from a uniform point source of one candle. |
|
| luminous intensity |
cd (candela) |
The power of a light source: the luminous intensity or the flow of light in a given direction, where 1 cd = 1 lm/sr. |
|
| lux of illumination |
lx (lux) |
Unit of illumination, equal to one lumen per m? or to the illumination of a surface uniformly one meter distant from a point source of one candle. |
|
| overcast sky |
|
A sky luminance distribution three times brighter near (C.E.I. Standard Condition) the zenith than at the horizon, as defined by a formula proposed by Moon and Spencer in 1942 and adopted by the Commission Internationale de l'Eclairage (CIE) in 1955. |
|
| reflectance |
|
The ratio of reflected flux to incident flux. |
|
| RGB |
|
Additive primary system of a color as a mixture of red, green, and blue (RGB) primary colors. Each color component has 256 possible intensity values, making it possible to produce 16,777,216 unique colors. |
|
| specular reflection |
|
The process by which incident light is redirected at the specular (mirror) angle. |
|
| specular transmission |
|
The process by which incident flux passes through a surface or medium without scattering. |
|
| task light |
|
Light that is directed to a specific surface or area to provide illumination for visual tasks. |
|
| visual light transmittance |
|
The proportion of natural light that will travel through the component (glass, blind, etc.). |
|
| zenith |
|
The point on the celestial sphere that is directly above the observer. |
|
