In the previous article I described the two basic values of lighting: the intensity and luminous flux. Next step is the quantitative definition of light that affects or that is emitted from a surface.
There are two sizes qunatitative: illuminance and luminance.
The illumination is a quantity independent of the objective position of the surface observer, which measures the amount of light flux intercepted by a surface.
The illumination (E) medium on a surface is then given by the ratio of the luminous flux (Φ) emitted from a particular source and the receiving surface (A).
E = Φ / A = lm/m2 = lux (lx) is therefore the one lux illumination produced by a flow of a lumen im uniformly distributed over an area of 1m2
The luminance (L) is rather a subjective magnitude, depending on the position of the observer. Corresponds to the amount of light that actually reaches our eye.
The luminance (L) of an infinitesimal surface in a given direction is defined as the ratio of light intensity (I) emitted in that direction and the apparent area of the surface towards the observer (NB areal apparent means the projection of surface in the direction of the observer).
L = dI / dA cosβ = cd / m2 (β is the angle between the normal to the surface glowing and the observer)
observation intensity consistently decreases if the surface increases the luminance 
Mon, July 9, 2007
LIGHTING