There are 4 pieces of 18 Watt fluorescent lamps in the luminaire. Luminaire with four fluorescent lamps

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Question:

There are 4 pieces of 18 Watt fluorescent lamps in the luminaire. Luminaire with four fluorescent lamps provides 5200 lumens flux.
The luminaire is 60 cm tall and 60 cm wide. Luminaires will be placed on the ceiling with nearly 100% of the light flux on the working plane (direct
lighting). The length and width of the room are 40 meters X 20 meters, respectively. Make the lighting design of the room so that the brightness level can be 500 lux in the working plane.

Note: The efficiency of the luminaire is 60%. Room efficiency is given to you ready, you do not need to calculate, you will find the efficiency
It was determined as 57.7% from the table taken as 70%. Take the business factor 1.

Find the number of luminaire (fixture).