TrafficInfraTech Magazine Linking People Places & Progress
In a city that never sleeps, where nights are as vibrant as days, street lights offer the much-needed illumination for pedestrian and traffic safety, navigation, economic activity with extended business hours, beautification of the environment and promoting social inclusion by making public spaces accessible for outdoor activities. The onus of providing lighting to the megapolis lies on the street lighting department of the Brihanmumbai Electric Supply and Transport (BEST) Undertaking under the aegis of the Municipal Corporation of Greater Mumbai.
BEST with over 34,500 poles and 44,300 energy-efficient LED lamps has always been committed to illuminating Mumbai, ensuring the safety and comfort of its citizens, drivers, and pedestrians alike embracing eco-friendly practices. Our centralized automatic streetlight monitoring system (ASMS) exemplifies our innovation, providing real-time data to enhance operational efficiency and curb electricity theft. We take pride in our role in making Mumbai a city that truly never sleeps.
Anil Diggikar (IAS),
General Manager, BEST Undertaking
MCGM is responsible for, among others, providing street lights to Mumbai and has entrusted this task to the BEST Undertaking in its area of supply as per the provisions of the Mumbai Municipal Corporation Act 1888. While earlier BEST would install street lights with its own funds and recover the amount with interest from the corporation, it now maintains as well as executes street lighting under the All-in-Hire scheme wherein it charges MCGM on a monthly basis depending on number of lamps and their wattage.
Keeping the aims of public lighting in focus, which include permitting users of the road at night to move about with the greatest possible safety and comfort, where the driver would be able to see distinctly and locate with certainty and on time all significant details including the alignment of the road, traffic signs and possible obstacles and the pedestrian being able to see distinctly the edges of footways and vehicles, standards in street lighting have been established globally with additional local requirements. The average lux level is maintained at 40 on major roads, though the standard is 30 lux considering depreciation over the period of time.
Classifying Traffic Routes
Based on the code of practice for lighting of public thoroughfares, BEST has classified illumination of traffic routes into various groups. Main roads fall under Group A where the level of illumination and uniformity is high and the glare, minimum. They are further sub-divided into very important routes with rapid and dense traffic and those with mixed traffic like city streets, arterial roads and thoroughfares.
Secondary roads fall under Group B comprising those with considerable traffic, including principal local traffic routes and shopping streets and those with light traffic. Residential and unclassified roads, bridges and flyovers, town and city centres and those with special requirements near airfields, railways and docks are also classified into groups.
Designing Street Lighting
There are multiple factors to be considered while designing street lighting as recommended by the international Commission on Illumination (CIE). Some of them include average road luminance, brightness uniformity, longitudinal uniformity, glare, environmental ratio SR, Colour Rendering Index (CRI) and visual inducement.
Road Luminance is a measure of the visibility of the road. It is the most important factor, affecting whether the obstacle can be seen and is based on the principle of illuminating the road enough to see the outline of the obstacle. Brightness depends on the light distribution of the luminaire, the lumen output of the luminaire, the installation design of the street lighting, and the reflective properties of the road surface. The higher the brightness level, the better the lighting effect.
Uniformity is an index to measure the uniformity of light distribution on the road, which can be expressed as overall uniformity (U0) and longitudinal uniformity (UI). Glare is the blinding sensation that occurs when the brightness of light exceeds the level of adaptation of the human eye to light. It can cause discomfort and reduce road visibility. Road lighting should not only illuminate the road, but also the adjacent area so that motorists can see surrounding objects and anticipate possible road obstacles (e.g. pedestrians about to step onto the road). SR is the visibility of the road perimeter relative to the main road itself.
The colour rendering index measures the ability of artificial light sources to display or reproduce the colour of the road or objects on the road relative to natural light sources. The natural light source (Sun) has a CRI of 100. The higher the index, the better the visibility.Through the guidance auxiliary facilities of the road, such as the centreline of the road, the curb, the road sign, the driver can know his position and the direction in front of the road. This is visual inducement.
Four fundamental types of siting arrangements are recognized in street lighting. Single side arrangement, where all the luminaires are on one side of the road. This is recommended only when the width of the road is equal to or less than the mounting height. Staggered arrangement, where the luminaires are placed on either side of the road in a zigzag formation. This is recommended when the road width is 1 to 1.5 times that of the mounting height. Opposite mounting, where the luminaires are situated on either side of the road opposite to one another. This is advisable for road widths more than 1.5 times that of the mounting height, and axial mounting, where the luminaires are placed along the axis of the road. This is recommended for narrow roads the width of which do not exceed the mounting height.
Lighting Poles
BEST also pays particular attention to the choice of lighting poles which are made out of mild steel tubular ERW pipe. The portion above the ground is painted with Al paint and the one below with black Bitumen. One sixth of the height of the pole is buried under the ground. The pole is provided with a sleeve at this position such that half the portion of this sleeve is buried underground, which is the main point of contact for corrosion. A concrete foundation is placed to support the pole with an apron.
Poles used are of different types: the Step Drawn pole, which is a hot rolled tube of high tensile steel & step-drawn with uniform thickness throughout its length and manufactured from single piece steel tubular pipe and the Swaged pole which is made from three different length of steel tube of different diameters.
The Street Light Department of BEST Undertaking carries out the design, installation and maintenance of street lighting assets in the Mumbai Island City limits. Currently, around 34,539 number of street lighting poles with 44,300 illuminating lamps of different types and wattages are being maintained by the undertaking. The Street Lighting (Maintenance) Department staff is available 24×7. BEST Undertaking has replaced HPSV lamps with the more energy-efficient LED lamps for street lighting and 2 x 15watt LED in decorative garden lanterns. It has incorporated eco-friendly practices such as the use of amorphous core transformers and energy-efficient street lighting.
For better management of streetlights, BEST has adopted a centralised automatic streetlight monitoring system (ASMS). All street lights in the city are operated and maintained through a web-based interface and sensors installed at every SLP will provide information of electric supply to a particular pole. This will help curb electricity theft. Updated information on malfunctioning lights or poles with its GPS location will be provided every 15 minutes.
A unique feature of BEST’s services is group control of street lighting based on sunset and sunrise timing through ASMS and switching on/off of lights and lanterns by electronic timers using an astronomical calendar accommodating seasonal variations.
Challenges exist, including staff resistance to technology, implementation logistics in a densely populated city like Mumbai and electricity theft but the outstanding service of BEST has kept the maximum city humming throughout the night, every night.