Today, LED meets the requirement for one of the most complex lighting applications – Sports Lighting. And behind the success of, otherwise, tiny LED chips are extensive research on optics for controlling and shaping the light emitted from such chips. The two basic optics required for shaping, distributing and controlling the light emitted by an LED (theoretically 360°) are:
- Primary Lens
- Secondary Lens
A Primary Lens narrows the initial beam angle to a more manageable range. A lens can be designed to cater to angles from 180 to as low as 60 degrees or even lower. Light emitting efficiency is proportional to the angle (the higher the angle, the greater the efficiency). The lens is directly glued on the chip holder to encapsulate the chip, which in turn becomes an integral part of the LED source.
The reflow soldering process is used to attach the pre-encapsulated LED component to a PCB, and because of its highly automated nature high volumes of soldering can be achieved. A primary lens is a double convex lens, and to set the desired angle the distance between the lens and the LED is adjusted (the angle is inversely proportional to the distance).
A Secondary Lens is located on the exterior of the LED with a Primary Lens. This lens is designed to converge the light emitting angle of the LED light source to a desired angle between 5° and 160°. The three main geometrical distributions of the light field achieved through this are circle, ellipse and rectangle.
There are different types of lenses used for secondary optics, the most popular being TIR Lens working on the principle of total internal reflection. This type of lens enables more control over light and also provides rotationally symmetric designs for round light distribution. For multiple LEDs such lenses can be designed in arrays.
Source: Osram
Sports Lighting
One of the most complex of all requirements in general lighting has been in design of Sports lighting. LEDs have several benefits over their conventional counterparts. Some of the benefits are energy efficiency, longer lifespan, instant on/off capabilities, improved light quality, enhanced control, mercury free, pollution free and especially applicable for sports – flicker free. But in order to qualify, LEDs were required to meet the following critical requirements:
- Player visibility, which is very important for day-night cricket matches
- Light spill and Glare control
- Long throw illumination from High masts
- Wider beams for covering larger areas closer to the ground
- To meet high definition (HD) TV broadcasting of major sports events
Optics
The intended beam pattern and light distribution for a particular sports and arena depends on precise alignment of the LEDs with the Primary and Secondary optics, and accurate positioning in the luminaire. Nowadays, a large variety of LED modules are available. This, in turn, allows greater flexibility in configuring the luminaires with different numbers of LED modules and optics for achieving desired output levels.
Other than the Primary lens which collimate the light, and the Secondary lens which provides the desired light pattern, specialised optics with sharp cut-off angles are employed for minimising light spill and glare. Frosted or patterned materials are sometimes used as diffusers to soften the light for player and spectator. Flexibility in luminaire design has got a further boost with the advent of microlenses. These are very small lenses which are either integrated into or placed on top of the Primary or Secondary lens. They can either be fabricated directly on the surface of a Primary or Secondary lens, or a separate sheet can also be placed over the LED matrix or Secondary optics. The microlenses have been successfully used for – a) finer control of the light beam; b) homogenising the light output resulting in reduction of colour and intensity variations across the beam; c) highly precise shaping of beam pattern; d) reduction of glare by diffusing the light at a small scale.
desired photometric distribution
For microlenses, materials similar to Secondary lens are used. As high-powered LEDs generate significant heat, luminaire design incorporates proper heat sinks and other thermal management techniques to effectively dissipate heat for a long lifespan and consistent performance of the LEDs and optics. For sports lighting in tropical countries, silicone is often used as a material for microlenses. With development of suitable software for performing optics simulation, a luminaire designer may have to download ray set files for their high-brightness LEDs.
Rapid development in optics has enhanced the capabilities of LED sources to an extent that it has not only overpowered the traditional light sources, the flexibility in adopting LEDs in sports lighting, considered the most complex of lighting design solutions has brought about a sort of renaissance in illumination science.
Installations
There are many instances, apart from newer installations where LED luminaires have replaced the traditional floodlight luminaires.
- Most of Tennis Grand Slam stadia
- Many stadiums in Australia and New Zealand, where FIFA Women’s World Cup 2023 were hosted
- Yankee Stadium, New York and Fenway Park, Boston for Baseball
- Most of the Tennis Arenas hosting Grand Slam Tournaments across the world. Tennis requires flicker-free illumination
Back in India, the following major Cricket Stadia have undergone upgrades to replace traditional metal halides with LED systems for capitalising on the benefits.
- Eden Gardens Kolkata – The first installation for day-night cricket consisted of 864 single-ended filament 2kW Metal Halide Floodlights across four towers. Later upgraded to 400V double-ended filament 2kW Metal Halide Lamps. To achieve higher illumination levels for HD TV broadcasting and also improve energy efficiency, the stadium underwent further upgradation to a new LED system. The major achievement was about 40% reduction in several luminaires and huge power savings to the tune of 700kW. The illuminance achieved was 2500 lux (vertical) on pitch; 2000 lux on the 30-yard circle, and 1500 lux on the outfield.
- Wankhede Stadium Mumbai – The upgrade to the LED lighting system was carried out by Bajaj Electricals in time for the India vs England T20 match on February 2, 2025. Here the HID floodlights were replaced with 448 advanced 1650W LED floodlights. It was a next-generation LED lighting designed to include DMX controls, scene customisation and enhanced energy management.
Biswajit Sengupta is an MTech, Chartered Engineer, Fellow of Institution of Engineers (FIE), Fellow of Indian Society of Lighting Engineers (FISLE). He has over 35 years’ experience in lighting industry. He co-founded School of Illumination (SISED) at Jadavpur University. Successfully organized Lux Pacifica (international conference in Lighting) in Calcutta in 2015 as Secretary, Technical Committee. At present he is an Independent Lighting Consultant on Illumination Design and Engineering including LED and Fibre Optic Lighting, Circadian Lighting Design; Luminaire and Lamp manufacturing; Sourcing; Solar Energy consultancy & training.
