The use coefficient depending on the room size and wall floor material, its value is different. Room coefficient = Room Room L × W / high room (room + room wide) general classroom ceiling, walls, floors reflectivity of 70%, 50%, 30%. Their respective values ​​of different lamps is also different, in a lighting fixture is selected, the room coefficient corresponding the Cikuan lighting of said transmission rate (generally its products various data) can be investigated using the coefficient can be obtained from the lighting fixture manufacturers. The prices of different sizes, different types of lamps, the use coefficient absolutely different. I generally looked at general usage factor between 0.3-0.8, if not what conditions is 0.6 I think is wrong with. The other upstairs interpretation all came clear, the various values ​​into the formula to calculate the number of lamps. But one thing should remind you that power density requirements: 11.00W/m2 the mandatory targets must be reached. But also guarantee 300Lx illuminance, therefore, its essence is to use highly efficient lamps (90Lm / W lamps) over the color temperature of the lighting between 3500-5000K, CRI Ra 80 or more.