Question

A manufacturing operation requires 50 fc on the workplane in a 100 ft x 150 ft facility. The walls and ceilings are painted white. The work plane is 25 feet below the lights.

1. Calculate how many high-bay 400-W metal halide fixtures are required

2. Calculate how many 6-lamp T8 HBF fixtures are required.

Answer 1

Given data,

Both walls and ceilings are white ,

Rc = reflectivity of ceiling = 100%
Rw = reflectivity of walls = 100%

Ew = 50 fc ,

H = height = 25 ft,
W = width = 150 ft ,
L = length = 100 ft ,

Area of work plane (A) = W*L = 15000 ft² ,

Room-Cavity Ratio (RCR)

RCR = 5H*(W + L) / (W*L)

        = 5*25*(150 + 100) / (150*100)

        = 2.08 ~ 2

1. Number of high-bay 400-W metal halide (N)

From CU table,

Coefficient of Utilization (CU) for 400-W metal halide = 0.80
Lumens Per Fixture (LPF) for 400-W metal halide = 23,500 lm

Now,

N = (Ew * A) / (CU * LPF)

   = (50 * (100 * 150)) / (.80 x 23,500)

   = 39.89 ~ 40 lights

2. Number of 6-lamp T8 HBF (N)

Coefficient of Utilization (CU) for 6-lamp T8 HBF = 0.82
Lumens Per Fixture (LPF) for 6-lamp T8 HBF = 20,500 lm

N = (Ew * A) / (CU * LPF)

   = (50 * (100 * 150)) / (.82 x 23,500)

   = 44.61 ~ 45 lights