Utilization Factor of Liminaires

  1. Indoor Decorative Luminaire (Mirror Optic Type Philips TCS 36/236) with 2 no. 1200 mm 36 / 40 W Fluorescent Lamp

    Utilization Factor: MO Fitting
    Reflection factorDRR
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization 
    A0.60.320.270.230.310.270.230.260.230.310
    B0.80.400.340.310.390.340.300.340.300.412
    C1.00.450.400.370.440.400.360.390.360.495
    D1.250.510.460.430.490.450.420.450.420.576
    E1.50.540.500.470.530.490.460.490.460.635
    F2.00.600.560.530.580.550.530.540.520.723
    G2.50.630.600.570.610.590.570.580.560.777
    H3.00.650.630.600.640.610.600.600.590.814
    I4.00.680.660.640.660.640.630.630.620.857
    J5.00.690.670.660.670.660.650.650.640.883

    Note: The above figure is based on the efficiency of luminaire as 75 %.

  2. Box Type Fitting with 1 no. 1200 mm Fluorescent Lamp and Stove Enameled Channel

    Utilization Factor: Box Fitting
    Reflection factorDirect Ratio
    Floor30 %30 %30 %
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %50 %30 %10 %
    Room IndexCoefficient of Utilization 
    A0.60.290.230.180.270.210.170.240.200.160.27
    B0.80.420.340.280.380.300.250.330.270.230.31
    C1.00.480.400.330.420.360.310.380.320.270.37
    D1.250.550.470.400.480.420.360.420.370.320.43
    E1.50.590.520.450.520.450.400.460.390.360.48
    F2.00.670.590.530.580.530.470.510.460.410.55
    G2.50.720.640.580.630.570.520.550.500.460.60
    H3.00.760.690.630.660.610.560.570.540.500.65
    I4.00.810.750.710.710.660.620.610.570.550.70
    J5.00.860.800.750.740.690.660.640.610.570.74

Mainly Direct Fittings

  1. Direct (A) Standard Dispersive Reflector for Gas filled Lamps and for 85 W & 125 W Mercury Lamps (type MB/U) and Sodium Vapour Lamps (Type SO). Also for Open top and Closed top Enamelled and Translucents Troughs for Fluorescent Lamps (type MCF/U). Typical Efficiency is 70 % (Down) and typical outline is given below:

    Utilization Factor: Direct (Standard Dispersive Reflector)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.330.280.240.320.280.240.270.24
    B0.410.360.330.400.360.330.360.33
    C0.440.400.380.430.400.370.400.37
    D0.470.440.420.460.430.410.430.41
    E0.500.470.450.490.460.440.460.44
    F0.530.500.480.520.490.470.490.47
    G0.560.520.510.550.530.500.530.50
    H0.590.560.540.580.560.530.560.53
    I0.620.590.570.610.590.560.590.56
    J0.640.620.600.630.610.590.610.59
  2. Direct (A) Dispersive Reflector for 250/400W Mercury Lamps (Type MA/V) and 80 / 400 W (MBF/U) Concentrating Enamelled Reflector for 80 / 125 W (MB/U) Mercury, Sodium (SO/H) and Gas filled Lamps. Typical efficiency is 60 % (Down) and typical outline is given below:

    Utilization Factor: Direct (Dispersive Reflector)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.300.250.220.290.250.220.250.22
    B0.360.330.310.360.320.300.320.30
    C0.390.360.340.390.350.330.350.33
    D0.420.390.370.420.380.360.380.36
    E0.450.420.400.450.410.390.410.39
    F0.480.450.430.480.440.420.440.42
    G0.510.480.460.510.470.450.470.45
    H0.540.510.490.540.500.480.500.48
    I0.560.540.520.560.530.510.530.51
    J0.580.560.540.570.550.530.540.53
  3. Direct (B) Reflectors with Enclosed Globe such as Industrial Diffusing Lighting for Gas filled Lampsor for Blended Light (MBT) Lamps. Also Open Reflector for Mercury Tungsten Lamps (MAT). Typical Efficiency is 50 to 60 % (Down) and typical outline is given below:

    Utilization Factor: Direct (Reflector with Enclosed Globe)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.280.250.220.260.230.200.220.20
    B0.340.300.270.310.290.270.280.26
    C0.390.340.320.360.340.320.320.31
    D0.430.380.360.400.380.360.360.35
    E0.470.420.400.440.420.400.400.39
    F0.500.450.430.470.450.430.430.42
    G0.530.480.460.500.480.460.460.45
    H0.550.510.490.530.510.490.490.48
    I0.570.530.510.540.520.500.500.49
    J0.580.540.520.550.550.510.510.50
  4. Semi-Direct Wide mouth Opal Fitting for Gas filled Lamps. Diffusing Fluorescent Fitting. Typical efficiency is 55 % (Down) & 16 % (Up) and typical outline is given below:

    Utilization Factor: Semi-direct (Wide Mouth Opal)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.270.240.220.260.230.210.220.20
    B0.310.280.260.300.270.250.260.24
    C0.350.320.300.340.310.280.300.28
    D0.390.360.340.380.340.310.330.31
    E0.420.390.370.410.370.340.360.34
    F0.450.420.400.440.400.370.390.37
    G0.480.450.430.470.430.400.410.39
    H0.510.480.460.490.450.420.430.41
    I0.540.510.480.510.470.440.450.43
    J0.560.530.500.530.490.460.470.45

    Note: In case of multi lamp fittings housing two to three lamps, the coefficient of utilization will be 0.85 to 0.9 times the figure given in above table.

    Cover Glasses: When for mainly direct fitting, a fron cover of glass is fitted to reduce the brightness or to exclude dirt, an additional allowance must be made for the light absorption, depending on the shape, type and quality of the glass. As a general rule, the above figures should be multiplied by 0.7 for flashed opal, 0.75 for frosted and 0.9 for clear glass, but a definite figure can be obtained from the manufacturer.

  5. Semi Direct Batten type and V-channel type Fittings for Fluorescent Lamps (Type MCF/U). Typical efficiency is 60 % (Down), 25 % (Up) and typical outline is given below:

    Utilization Factor: Semi-direct (Batten Type)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.300.250.210.270.22Not generally to be recommended with dark surroundings on account of the likelyhood of discomfirt glare.
    B0.380.320.280.340.29
    C0.420.360.330.390.34
    D0.460.410.370.430.38
    E0.500.450.400.470.42
    F0.550.500.450.510.45
    G0.600.540.490.540.49
    H0.630.580.520.570.52
    I0.670.620.570.590.54
    J0.700.650.600.610.56

General Diffusing Fittings

  1. General Diffusing. Enclosed Diffusing Fitting of Flashed Opal Glass. Typical efficiency is 45 % (Down), 35 % (Up) and typical outline is given below:

    Utilization Factor: Diffusing (Enclosed)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.260.210.180.220.180.160.170.15
    B0.310.260.220.270.230.200.200.18
    C0.350.300.260.310.270.240.230.21
    D0.380.330.300.340.300.270.260.24
    E0.410.370.330.370.330.300.290.27
    F0.440.400.360.400.360.330.320.30
    G0.470.430.390.430.390.360.350.33
    H0.500.470.420.450.410.380.370.36
    I0.530.500.450.470.430.400.390.38
    J0.560.530.480.490.450.420.410.40
  2. Frame type with Diffusing sides, open above, ribbed glass or louvered beneath, Suspended. Typical efficiency is 35 % (Down), 45 % (Up) and typical outline is given below:

    Utilization Factor: Diffusing (Frame Type)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.260.230.210.230.21 
    B0.320.290.270.280.26
    C0.350.320.310.310.29
    D0.380.350.340.340.32
    E0.410.380.370.370.35
    F0.440.410.400.400.38
    G0.470.440.430.420.41
    H0.500.470.460.440.43
    I0.530.500.490.460.45
    J0.550.520.510.480.46

Mainly Indirect Fittings

  1. Semi Indirect. Open above, Louvered beneath. Typical efficiency is 20 % (Down), 55 % (Up) and typical outline is given below:

    Utilization Factor: Semi-indirect
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.200.160.140.190.14The coefficients are based on a 75% luminous efficiency of fitting, and will need additional judgament in proportion when using fittings of higher or liwer efficiency. These fittings are suitable for use in rooms with light coloured decorations.
    B0.260.210.180.240.18
    C0.310.250.220.270.22
    D0.350.290.260.300.26
    E0.390.340.300.330.30
    F0.430.380.340.360.34
    G0.460.420.380.390.37
    H0.500.460.420.420.40
    I0.530.490.460.440.42
    J0.560.520.500.460.44
  2. Indirect (A). Pendant Fittings and Throughs giving all their light output in an upward direction, but without sharp directional control of light. Typical efficiency is 75 % (Up) and typical outline is given below:

    Utilization Factor: Indirect (Pendant)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.150.120.100.100.08The coefficients are based on a 75% luminous efficiency of fitting, and will need additional judgament in proportion when using fittings of higher or liwer efficiency. These fittings are suitable for use in rooms with light coloured decorations.
    B0.180.160.130.120.10
    C0.210.190.160.140.12
    D0.240.220.190.160.14
    E0.270.250.220.180.16
    F0.300.280.250.200.18
    G0.330.300.270.220.20
    H0.360.320.290.230.21
    I0.380.340.310.240.22
    J0.400.360.330.250.23
  3. Indirect (B). Cornices, Recessed Covers and Collars giving all their light above Horizontal.

    Utilization Factor: Indirect (Cornices)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.080.060.050.050.04These coefficients are based on a 40% liminous efficiency of the fixture, but details of construction may vary this figure very considerably.
    B0.100.080.070.070.06
    C0.120.100.090.080.07
    D0.130.110.100.090.08
    E0.150.130.110.100.09
    F0.170.150.130.110.10
    G0.180.160.150.120.11
    H0.190.180.160.130.12
    I0.210.200.180.140.13
    J0.220.210.200.150.14
  4. Louvered Ceilings.

    Utilization Factor: Indirect (Louvered Ceiling)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.210.180.17Light angle 40o, Opaque louvers with reflection factor 75%, Ceiling cavity reflection factor 75%. No reflectors.
    B0.250.210.20
    C0.280.240.23
    D0.300.270.26
    E0.320.290.28
    F0.340.310.30
    G0.360.330.32
    H0.370.350.34
    I0.380.360.36
    J0.390.370.37
  5. Louvered Ceilings.

    Utilization Factor: Indirect (Louvered Ceiling)
    Reflection factor
    Ceiling70 %50 %30 %
    Wall50 %30 %10 %50 %30 %10 %30 %10 %
    Room IndexCoefficient of Utilization
    A0.230.170.14Based on reflection factor of ceiling cavity 75%. Cavity reasonably free from obstructions and having depth not exceeding one third of its width. Absorption of translucent louvers 10%.
    B0.280.240.20
    C0.340.290.25
    D0.380.330.30
    E0.420.380.35
    F0.460.430.40
    G0.490.460.43
    H0.520.490.47
    I0.550.520.50
    J0.570.550.53

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