Light Flux (Ø): The light energy, coming out of a light source, which is radiated at unit time at frequencies within the limits of eye. Its unit is "lumen", showed as lm.
Light Intensity(/): The light flux intensity radiated in a certain direction (space angle) form apoint light source. Its unit is "candela".
Space Angle(•): The cone which reserves 1 m pf space on the surface of a sphere with 1 m2 of diameter is called 1 steradian of space angle.
Brightness Level (E): Sum of light fluxes that fall onto a unit space. Its unit is "lux"
Eave, average brigtness level
E, point brightness level
S, surface level
d, the distance between source and illuminated surface
•, the angle between normal of the surface and light source
Luminance ( ): The ratio of the light intensity which directly the eye from light sources or by reflecting from illuminated surfaces to the projection in ivew direction of the surface. Luminance is ehat affects as brightness to our eye. Its unit is "nit", "stlib" or "asb".
1 nit=1cd/1 m2 1stilb=1cd/1 cm2 L=I/S xcos•
Glare: The luminance value which is disturbing for the eye.
Efficacy factor: The light flux given by a light source per unit power. It is the indicator of the light source.
Uniformity: The ratio of the luminance level of the darkest spot of an illuminated place to the average luminance level. This ratio must be equal to or higher than 0.8.
Colour Temperature: The warmness or coolness degree of a light source. It is expressed in Calvin terms. There is inverse proportion in colour temperature. For examplei 2700 oK is a warm color, whereas 6000 oK is rather cool.
Colour temperature and colour rendering standard presentation which is found on fluorescent lamps is given below.
Code Explanations
International Colour Sign
The first number is for colour rendering
Following numbers define colour temperature.
Reflecting factor (•): The ratio of light flux reflected from surface to the light flux coming to the surface.
Conveyance factor (
Absorption factor (•): The ratio of light flux absorbed by the surface to the light flux coming to the surface.
Stroboscopic Event
In an environment illuminated with gas discharged lamps, the rotation movement or harmonic movement of objects can be misperceived by the eye; this is called stroboscopic event. For example, in a place where such an effect occurs, an object which turns clockwise can be percevied as if it is turning counterclockwise, or an object which turns counterclýckwise can be perceived if it is turning clockwise or as if it stops completely, In order to prevent ths effect from happening:
1-An electronic ballast can be used.
2-Illumination can be supported with incandescent or halogen lamps.
3-If as-discharged lamps are supplied with single phase, a place difference can be created between the flows of lamps.
4-If gas discharged lamps are supplied by three phases, these phases can be evenly distributed
Light Distribution Curves
Light distribution curves are drawn where bare light source flux is 1000 lumens. Light distribution curves give information about light source and luminaire. Light distribution curves and diagrams can appear in a variety of forms depending of the type of luminaire and light source.
Polar Light Intensity Curve
This curve expresses light intensity distribution in terms of candalas (cd) and shows the shape of light distribution.
Conic Light Intensity Diagram
These are the graps which give the efficacy of the light source from its end point to the area that it illuminates especially as regards spot luminaires.
Figure-1
In the curve shoen at figure 1, thick lines show light intensity on breadthwise surface, and dashed lines show the light intensity on lengthwise surface. The curve in figure 1 is the curve especially used for direct and indirect fluorescent luminaires. Curves of the luminaires defined as downlight and uplight are also similar and are read in the same manner.
Figure-2
As can be seen in figure 2, brightness intensity changes at every elevation level. For example, it is 1450 lx where light source is hold at 1 meter above, and 91 lx where the light source is hold at 4 meters above.
