State the various lighting calculations methods and Describe any one of them.

State the various lighting calculations methods and Describe any one of them.
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1 Answer

Answer :

Lighting calculation methods:

1. Lumens or Light flux method

2. Point to point or Inverse Square law method

3. Watts per Square meter method


i) Lumens or Light flux method: This method is applied where an average illumination is required. Total lumens output is calculated from the efficiency of each lamp and the number of lamps used in the circuit. To calculate lumens received on the working plane, the total lumens already calculated is multiplied by the co-efficient of utilization. When the lamps & the surroundings are not perfectly clean, then while calculating the lumens received on the working plane, the depreciation factor or maintenance factor is taken into consideration,
Thus lumens received on working plane =(Number of lamps× wattage of each lamp × efficiency of each lamp × coefficient of utilization) / (depreciation factor)

OR

= number of lamps × wattage of each lamp× efficiency of each lamp × utilization factor ×maintenance factor

OR

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ii) Point to point or Inverse Square law method:- 
This method is applied where the illumination is required at a point due to one or more sources of light. The illumination at any point within the range of lamp can be calculated from the inverse square Law, if a polar curve of lamp and candle power of lamp reflected by its reflector in different directions is known. If two or more lamps are illuminating the same working plane, illumination due to each can be calculated and added. This method is not commonly used due to more complications involved in its calculations. However, It is used in flood lighting & the yard lighting calculations.

iii) Watts per Square meter method:- Basically it is a thumb rule method. It is very handy for rough calculation or checking. While applying this method, we allow watts/square meter of area to be illuminated is taken according to the illumination desired on an average value considering overall efficiency of the lighting system.
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