Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-2)


(3) AS per Deutsch Norm DIN 5035

  • In this Method the working plane divide into a number of sections which are at least rectangular, of ratio of length to side not less than 1: 2 but which are preferably of square shape.
  • A square grid of minimum size 1 meter is established within each section with a measurement point at the centre of each square.
  • The grid module defining the measurement points is selected so as not to coincide with the luminaire grid in either principal direction.
  • In exceptionally large interiors the grid size may be up to 5 meters. there is not any mention of accuracy limits of the method, but this is not surprising given the flexibility which the user of the method is allowed in choice of grid size.
  • The DIN system is the only one of the three methods studied to give any advice concerning illuminance measurements in obstructed interiors. Areas of the working plane located between large obstructions are treated for measurement purposes as separate spaces.

1

OUTDOOR ILLUMINATION (LUX LEVEL) MEASUREMENT

 (1) Nine Point Method for Determining Lux Levels in Street Lighting

  •  The Lux Level of Street Light is measured by 9-point method.
  • We need to make two equal quadrants between two light poles and between Pole and Rode edge.
  • Two Measuring Points below Light Pole (A1,A2)  and Two opposite side of Pole at Road Edge (A3,A4).
  • Two Point between Pole and Road edge (B1,B3).
  • One Point Between Pole  (B2) and on One Point between opposite side of Pole at road edge (B4)
  • One Point is at centre (C1).
  • Average Lux = (A1+A2+A3+A4)/16 + (B1+B2+B3+B4)/8 +C1/4

2

  • Solution
26 Lux 27 Lux 13 Lux
12 Lux 15 Lux 14 Lux
26 Lux 32 Lux 22 Lux
  • Average Lux = (A1+A2+A3+A4)/16 + (B1+B2+B3+B4)/8 +C1/4
  • Average Lux = (26+26+13+22)/16 + (12+27+14+32)/8 +15/4
  • Average Lux =20Lux 
MIN 12 Lux
MAX 32 Lux
AVG 20 Lux
U1=MIN/AVG 0.58
U2=MIN/MAX 0.38

 (2) As per Grid Point Set Up Measurement

  • Identify a horizontal grid of measurement points on the Illumination Measurement site surface. Locate measurement points on gridlines covering the test measurement area.
  • Ensure that the spacing between measurement points is uniform in both directions and is less than one-half the pole height or less than 4.5 Meter, whichever is smaller.
  • For installations with lights spaced less than 4.5 Meter apart, locate measurement points no farther apart that one-half the pole height, with at least three points between poles in both directions.
  • Record the location of all measurement grids and point layouts with dimensions from surrounding poles or other structures. Provide this information, including a sketch or rendering of the grid layouts.
  • For open areas such as main parking, make the measurement grid large enough to cover at least four poles of this Area layout and at least two Pole are covered.
  • For site perimeter open areas or areas adjacent to a building edge establish the test area measurement grid in a typical perimeter or building edge area. The depth of the test area should extend from the paved site boundary or building edge inward to the nearest line of light poles that are at least 4.5 Meter from the boundary or building edge.
  • The width of the test area must cover at least two of the poles in the line that is at least 4.5 Meter from the boundary or building edge.

(A) In Open Area

3

(B) In the Area of Site Perimeter

4

(C) Near Site Boundary Area:

5

Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-1)


Introduction:

  • Working plane illuminance (Lux Level) need to be measured in the field for cross check of whether the existing installation meets a design requirement or not.
  • Field surveys may also be useful to identifying the causes of complaints about lighting, hence the results of field surveys may be useful for the designer, installers and end users.
  • There are various methods are developed for field measurement of Interior Lighting and External Lighting.
  • The Measurement Methods recommended by the various national lighting bodies are generally similar or slightly derivatives to each other. The most common method / Standard is BEE, CIBSE, IES and DIN code
  • The most of methods require to measurement of illuminance at points on a grid at working-plane height or at Floor, but the grid size and position of the measuring points may be differed from various standard to standard.
  • The IES method and its derivatives use the position of the grid according to the luminaire locations.
  • The CIBSE and DIN methods use a position of grid according to the room size.
  • The techniques of analysis of the field measurement results also differ

Basic Requirements for Exterior & Interior Light Level Measurement

  •  The following Points should be considered for accurate measurement of interior and exterior lighting Lux level.
  • Where possible, use the same calibrated illuminance measurement meter (LUX Meter) If the same meter is not available, use the same make and model of calibrated meter to minimize error.
  • When taking measurements, verify that any objects/materials are not blocking any light to the meter head. The use of a remote meter head cabled to the meter body is recommended to prevent the operator from blocking the meter’s “view” of the lighting system being measured.
  • In Outdoor Lighting it is essential to measure of illuminance should be done in night (proper dark).
  • For indoor lighting, measurements with lights ON and Lights OFF technique can be followed and the daylight variation is not too much and the survey time is not too long.
  • In an installation of fluorescent discharge lamps, the lamps must be switched on at least 30 minutes before the measurement to allow for the lamps to be completely warmed up.
  • In many situations, the measuring plane may not be specified or even non-existent. Hence it is necessary to define measurement height, typically 0.8 to 1 meter from the ground or floor level.
  • The lux measurement procedure simply requires positioning a meter’s sensor on the surface or location where you wish to measure the incident light.
  • The sensor should face the light source at a right angle. If the sensor is not perpendicular to the light, the measurement will be incorrect, though some lux meters have a cosine correction to account for the angle.
  • Meters that require a colour correction factor may have a means of inputting the CCF to adjust the result for LEDs or fluorescent lights; otherwise, you will have to manually multiply the measured lux by the CCF.

 INDOOR ILLUMINATION (LUX LEVEL) MEASUREMENT.

 (1) As per Room Index Method (as per BEE Code / CIBSE Code):

  •  This methos is more suitable where measuring Plan / Points for an interior is more rectangular than square. First, we need to be found Room Index.
  • Based on the room index, the minimum number of illuminance measurement points is decided by Room Index Number
  • Room Index (RI) = (L x W) / H x (L+ W)
  • Where L = Length of Room
  • W = Width of Room
  • H= Height of the luminaires above the plane of measurement 

Table 4-2: Number of points for measuring illuminance

Room index

Minimum number of measurement points

 

For ± 5% accuracy

For ± 10% accuracy

RI < 1

8

4

1 < RI < 2

18

9

2 < RI < 3

32

16

RI > 3

50

25

 Sample calculation

  • Measure Illumination Level of an office room have length, L = 7.5 m and width W = 5 m,
  • Solution:
  • Suppose Height of Illumination from Floor is 2 Meter
  • Room Index RI = (L x W) / H x (L+ W)
  • Room Index RI = (7.5 x 5) / 2 x (7.5+ 5)
  • Room Index RI = 1.5
  • From Table 4.2 minimum Illumination Measure Points should be 18 No’s
  • The illuminance measurements Points with Measured Value in Lux are marked on the grid.  

1

Measurement Reading Details

107 Lux

99 Lux

85 Lux

65 Lux

65 Lux

45 Lux

73 Lux

130 Lux

105 Lux

110 Lux

86 Lux

87 Lux

59 Lux

50 Lux

58 Lux

99 Lux

75 Lux

106 Lux

115 Lux

76 Lux

         

Min

45 Lux

     

Max

130 Lux

     

Average

85 Lux

     
         

U1=MIN/AVG

0.5 Lux

     

U2=MIN/MAX

0.3 Lux

     

 

 (2) As per Point Layout Method

  • For office and other task areas, identify a set of measurements points on desktops and other work surfaces that best represents lighting conditions in the space.
  • It may not be possible to develop a uniform spacing grid, but points should be chosen that represent the various lighting conditions across the space.
  • For each separate horizontal grid, identify a vertical plane representative of the lighting in the area (typically the gridline directly between two light fixtures).
  • On this vertical plane, set a grid (line) of points at 1.5 Meter above the site surface at each of the corresponding horizontal measurement points.
  • The following figures provide sample layouts for selecting horizontal measurement points for typical areas where lighting measurements are taken

2

Measurement Reading Details

107 Lux

80 Lux

100 Lux

75 Lux

100 Lux

65 Lux

73 Lux

70 Lux

75 Lux

60 Lux

99 Lux

87 Lux

95 Lux

58 Lux

98 Lux

60 Lux

65 Lux

63 Lux

66 Lux

78 Lux

75 Lux

78 Lux

62 Lux

99 Lux

87 Lux

95 Lux

58 Lux

98 Lux

         

Min

58 Lux

     

Max

107 Lux

     

Average

80 Lux

     
         

U0 or U1=MIN/AVG

0.7 Lux

     

Ul or U2=MIN/MAX

0.5 Lux

     

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