# Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-3)

## (3) Grid Method to measure illumination on the road

• The arrangement of the measuring points depends on the distance between the Illumination Pole and the width of the Road.
• The measurement of illuminance should be performed on the area in longitudinal direction two consecutive luminaires in the same row and in transverse direction the width of the area with the same illumination class, i.e. if the road and adjacent pavement or bicycle path have the same illumination class, they may be considered as one area during the measurements. The measuring points should be distributed evenly within the measuring field.
• The distance between the measuring points (D in Meter) in the longitudinal direction should be calculated using the formula
• The distance between the measuring point in longitude ( D)=S / N
• where:
S= the distance between the luminaires in [m],
N= the number of measurement points in the longitudinal direction,
for S ≤ 30 m, it is N = 10,
for S > 30 m, the smallest integer giving D ≤ 3 m.
• The distance between measurement points (d in Meter) in the transverse direction should be calculated with the formula:
• The distance between the measuring point in transverse (d) = Wr / n
• where: Wr= the width of the road or the area under consideration in Meter.
• n = the number of measurement points in the transverse direction equal to 3 or more and being an integer giving d ≤ 1.5 m.
• The distance between the points and the edges of the surface under consideration should be D/2 in the longitudinal direction and d/2 in the transverse direction. The location of the measurement points in the measuring field is shown in Figure.

## (4) Equal Space Method

• In this Method at least10 equal measuring Points are taken between two lighting Pole on one side of the Roadway.
• These measurement points cannot be spaced more than 5 meters apart. Two lines of measurement points are needed per driving lane, one-half lane width apart.
• Once you have taken all of your illuminance measurements, you can calculate an average illuminance for the section of roadway you have measured.

## What is Lighting Uniformity

• light uniformity refers to the uniformity of lighting in an environment. It is necessary to maintain the uniformity of light in order to make sure that everything is perfectly visible in the room.
• Uniformity is the ratio of the minimum lighting level to the average lighting level in a specified area.
• U1 = E Min / E Average
• U2 = E Min / E Maximum
• U & E stands for uniformity & illuminance respectively.
• Uniformity is a quality parameter for the overall illuminance distribution.
• It is quite useful to use this uniformity ratio to describe how the lights are evenly distributed on the ground. If the difference between minimum and average lux is small, then the ratio is high, which gives better light uniformity.
• The maximum lighting uniformity is 1, which means the lux levels in all the sampling points are the same. However, it is very unlikely to achieve this maximum value for artificial lighting.
• If the uniformity is very low for the outdoor or indoor lighting, the citizens, workers, or athletes might feel uncomfortable, and thus their vision is affected.
• The more uniform the light distribution, the better the illuminance and the more comfortable the visual experience.  The closer the illuminance uniformity is to 1, the better, otherwise the smaller the more visual fatigue.

## How to improve Lighting Uniformity

• Adjust the aiming angle of the floodlight,
• The lights irradiated by the floodlights should overlap each other,
• Use pole lights, high-power floodlights, street lights, etc. to supplement lighting.

## Light Uniformity Standard

• There are different light uniformity standards that need to be followed depending on the nature of the environment
• Most focus-intensive tasks require a uniformity index of around 0.6, whereas, technical drawing and other demanding tasks require a ratio of at least 0.7.
• Uniformity value greater than 0,60 is recommended in working areas. Because, above this level, the change in light levels cannot be sensed by people and that makes them comfortable. Proper lighting of the environment also helps employees work more comfortably when looking at the computer screen.
• Due to low uniformity in road lighting, the homogeneity of lighting will be distorted. So, very bright and very dark spots will occur on the road. If brightness changed very often, this will cause eye strain and stresses the drivers
• In order to avoid these situations, average uniformity value greater than 0.35 or 0.4 is required according to road lighting class.
 Standard Area Ratio of Minimum/Average Illumination UK CIBSE and German DIN guidelines The general lighting scheme 0.6 and 0.8 NBC-2005, page no 759 Working Area Not Less than 0.7
 Table-6: Recommended Levels of Illumination (BIS, 1981) Type of Road Road Characteristics Ratio of Minimum/Average Illumination A-1 Important traffic routes carrying fast traffic 0.4 A-2 Main roads carrying mixed traffic like city main roads/streets, arterial roads, throughways 0.4 B-1 Secondary roads with considerable traffic like local traffic routes, shopping streets 0.3 B-2 Secondary roads with light traffic 0.3
 EUROPEAN STANDARD- EN 12464-1:2011 Space Uniformity U0 (Emin / Em) Areas with traffic and corridors 0.4 Stairways, escalators, and travelators 0.4 Lifts 0.4 Loading bays 0.4 Coffee-break rooms 0.4 Technical facilities 0.4 Storage spaces 0.4 Electronics workshops, testing, and adjustments 0.7 Ball-mill areas and pulp plants 0.4 Offices and writing 0.6 Check-out areas 0.6 Waiting rooms 0.4 Kitchens 0.6 Parking areas 0.4 Classrooms 0.6 Auditoriums 0.6
 EUROPEAN STANDARD- EN 12464-1:2011 Task illuminance ≥ 0.7 Illuminance of immediate surrounding areas ≥ 0.5
 Football Field Lighting Design Nature of the Sports Field Required U1 Light Uniformity Class I such as for a National Competition ≥ 0.7 Class II such as for a League ≥ 0.6 Class III such as for a Training Ball Field ≥ 0.5 Industrial and Commercial Lighting Uniformity Requirement The Area The Light Uniformity Standard Highway 0.4-0.6 Sports field 0.5-0.8 Office 0.4-0.6 Parking Lot 0.4-0.5 Warehouse 0.4-0.6 Running Track 0.3-0.5 Airport 0.2-0.3