An illuminance of 600 lux is going to be provided to an office by using 3 x 28 W T5 recessed fluorescent luminaires (3200 lumen output for each 1200 mm long T5 fluorescent tube) on a reference plane of 0.8m above floor level with acceptable uniformity. The dimensions of the office are 18 m (L) x 12 m (W) x 3.2 m (H) and the reflectance of ceiling, wall and reference planes are 0.7, 0.5 and 0.2 respectively. The tubes are group replaced every 12,000 hours. The luminaires and room surfaces are cleaned once every two years. The cleanliness of the environment can be considered "clean". The typical Utilization Factor table is shown as below: Utilization Factor Room Reflectance C 0.7 05 W 0.5 0.3 F 02 0.2 1 1.5 0.47 0.51 SHR = 1.5. SHRNOM = 1.0 Room Index 2 2.5 0.53 0.54 0.56 0.51 0.53 0.55 0.51 0.53 0.53 0.54 3 4 S 0.57 0.56 Calculate the minimum number of luminaires required to achieve a maintained illuminance of 600 lux on a reference plane 0.8m above floor level with acceptable uniformity.