Incorrectly executed lighting can not only create discomfort, but also to become etiology of eyes. Therefore to design and mounting of the power supply network, and in particular, to determination of number of lamps, it is necessary to belong responsibly.

- - tape measure;
- - calculator;
- - table with safety factors;
- - table with utilization coefficients.

1. Measure by means of tape measure length, width and floor-to-ceiling height for which it is necessary to calculate the number of lamps. Find room space, that is increase its length by width.

2. Determine safety factor. Its indicator depends on intensity of use of lamps, extent of pollution of these luminous sources and frequency of their technical maintenance. The value of coefficient can vary ranging from 1.2 and 2. Determination of this coefficient is carried out on the basis of special tables.

3. Find utilization coefficient. For this purpose according to special tables at first find coefficient of reflection of ceiling, walls and also floor. So, the surface of white color reflects light for 70-80%, light surface – for 50%, the surface painted in gray color - for 30%, dark gray surface – 20% and dark surface is capable to reflect light only for 10%. Knowing it, calculate utilization coefficient by formula: φ=S / (h1-h2) (a+b)), in which φ - utilization coefficient, S – the room space, h1 – floor-to-ceiling height, h2 – height of rated surface, and (a+b) – the half-perimeter, that is the sum of length and width of the room.

4. Calculate the necessary number of lamps by formula: N = (E*S) / (U*n*Fl*Kz), where N – the number of necessary lamps, E – the necessary illumination of horizontal surface, U – utilization coefficient, n - quantity of lamps in one lighting instrument, Fl – luminous flux of one lamp and Kz – safety factor.