Ruling parties in the Brihanmumbai Municipal Corporation-the Bharatiya Janata Party and the Shiv Sena-are engaged in a war of words over the BJP-initiated LED streetlight project along Marine Drive. While the BJP upholds the energy-efficiency of LED lights, the Sena claims the LED lights have “stolen the charm” of Marine Drive by replacing the yellow lights with white. The Sena has also contended that there are dark patches on the footpath, risking safety of pedestrians. Dipankar Saha, assistant professor at IIT’s Department of Electrical Engineering, and Chetan Solanki, associate professor in the Department of Energy Science and Engineering at IIT, explain how LED lighting works. They offer a detailed look at how energy-efficient the system is and what can be done to retain Marine Drive’s charm.
How does LED lighting work?
In an LED, there is a one-to-one relation in energy conversion. An LED street light is an integrated light that uses light-emitting diodes (LED) as its light source. The electrical energy directly converts into light energy, whereas, in a conventional filament light bulb, the energy mainly gets dissipated in the form of heat. It starts emitting light when it essentially becomes too hot. So, LED lighting is instantaneous as compared to the sodium vapour lamps that take up to 15 minutes to light up.
LED lights use 15 per cent of the energy of an incandescent bulb while generating more light per watt. While conventional light bulbs operate at a maximum efficiency of 5 per cent with 10-20 lumens/watt, LED lighting operate at 15-20 per cent efficiency with 90-100 lumens/watt. With more research and near ideal LED, it’s possible to get even better efficiency levels in future. An LED bulb uses one-sixth of the energy used by an incandescent light, which translates into savings in the electricity bill.
What are the pros?
LED streetlights last longer than other lights. They don’t have filaments that quickly burn out. This reduces maintenance. LEDs can produce 80 lumens per watt, while traditional streetlights can only muster 58 lumens per watt. Because of their energy efficiency and long lifespan, LED streetlights are advocated as a means to reduce carbon emission. Even Buckingham Palace and the Times Square New Year’s Eve ball are lit by LEDs. Life expectancy of an LED is 30,000-40,000 hours.
High initial investment is the biggest disadvantage of LED lighting. LEDs are best used for directional lighting. While an incandescent bulb will cost Rs 15-20, an LED light costs Rs 300-400. According to BEST president Arvind Dudhwadkar, LED lights along Marine Drive only produce 60 lumens and are directional so not enough light reaches the footpaths. For LED lighting in an industrial unit that pays Rs 7-8/unit, it will take one to two years to recover the amount spent on LED lights, whereas in a domestic setting, where we pay Rs 3-4/unit, it will take three to four years to recover the amount spent on LED lighting.
Solution: Switch to warm LED lights
According to Solanki, white warm light will be better for Marine Drive. In the Colour Rendering Index, true colour is visible better under yellowish light as it matches the solar system. “We can switch to warm white LEDs to retain the glow and use diffusers to reduce glare and make the streelights more omni-directional. Specialised lens design and adjustable mounting can help address the problem of light not reaching the footpaths, solving all the problems at Marine Drive,” he added.
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