Diffusers are needed to distribute the light emitted by LEDs evenly and reduce their glare. New materials in use today offer a host of advantages over older materials like glass.
By Shruti Mishra
High brightness LEDs are intense point sources of light and create bright spots of concentrated lights, known as LED hotspots, that can be harsh on the human eye. Therefore, to provide glare-free LED lighting, or to create wider viewing angles, designers often choose to diffuse the light emitted. This can be done by inserting thin films or sheets behind the lens that not only help to diffuse light transmission but also avoid unwanted glare.
If you go by the definition, a diffuser is an optical component with light-scattering properties, placed in the path of the light source to reduce the sharpness of shadows and thus smoothen the illumination. Diffusers ensure uniform illumination by LEDs and are therefore considered as an integral part of the total lighting system. The range of diffuser materials available today can have a dramatic effect on illumination.
Role of a diffuser
- Distributes light evenly
- Avoids creation of LED hotspots
- Provides a wider viewing angle
- Offers ease of fabrication
- Provides soft light
- Minimises blocking and allows more light to pass
Traditional vs new options
When it comes to choosing the right diffusive material, manufacturers need to consider a variety of factors like uniform light transmission and diffusion, toughness and durability, and ease of fabrication.
The traditional way of diffusing a point source uses a frosted glass positioned in front of the light source. The problem is that the absorption-coefficient of glass is quite high and blocks a large amount of the LED light.
Another challenge is that glass is rather bulky and increases the overall weight of the final product. Also, the glass materials often cannot efficiently hide the sources of light, and can result in hotspots. In addition, they do not possess adequate toughness and are prone to cracks during shipping and installation.
With miniaturisation becoming the buzzword, LED manufacturers began to develop innovative and cost-effective diffuser designs to stay in the competition. As a result, two see-through plastics—acrylic and polycarbonates (PC) – are today dominating the LED diffuser market. These two transparent and engineered plastics are steadily replacing glass in LED applications, since they have the twin benefits of giving design freedom and low absorption coefficient. But in the race to provide outstanding diffusion and light transmission, polycarbonate materials have outpaced acrylic solutions in LED lighting markets by providing better durability and impact resistance.
Polycarbonate solutions are said to be a breakthrough for LED lighting manufacturers, as they can be tailored to the specific needs of an application through the compounding process, thereby achieving light transmission greater than 90 per cent. They offer high clarity and purity, and also ensure optimum light transmission. Suresh V., market development manager, Covestro (India) Private Limited, says, “The light diffusion polycarbonates convert the point-shaped glary light from LEDs into homogeneous surface spread light with high luminous efficiency and excellent hotspot hiding.” Well, LEDs with acrylic material can get there as well, but add weight, complexity and cost to the overall luminaire design.
Additional advantages of polycarbonates
To begin with, polycarbonate resins are tough, which makes them ideal from both the security and the safety point of view. Beyond this, they have exceptional energy efficiency, resistance to vibration and the ability to operate even at low temperatures. Some other benefits are listed below.
Thermal stability: Even though they are energy-efficient, LED lighting systems tend to generate heat. And because the diffuser is placed very close to the light source, it must use a material with good thermal properties. Polycarbonate resins offer superior thermal stability compared to acrylic resins, and can also withstand extreme temperatures.
Flame retardancy: The manufacturers of high powered LED lights are widely using polycarbonates as the diffusive material, because these are the only transparent plastic resins that are ignition-resistant and provide flame retardancy at a reasonable cost.
Design flexibility: Unlike the conventional fluorescent lights, the LED lighting industry can experiment with a range of aesthetic configurations. The polycarbonate solutions possess inherent design flexibility and can be moulded to form unique designs, which can be leveraged to meet certain light diffusion criteria.
Longer life span: Glass and plastics, other than polycarbonates, have a relatively high absorption coefficient, which forces manufacturers to overdrive the LEDs. This shortens their life. Polycarbonate resins or sheets are more durable and have high mechanical integrity, which helps to cut down on the cost of replacement.
A look at the latest materials
Many leading chemical companies across the globe are engaged in offering remarkable technological advancements in the field of polycarbonate diffusers to further enhance their performance. Covestro produces polycarbonate resins, films and sheets under trade name Makrolon which is widely accepted and used for the diffuser application globally.
The Makrolon diffuser materials are used for injection moulded, injection blow moulded and extruded diffuser parts, which create smooth and uniform light emissions and avoid unwanted glare. The high quality materials leads to a uniform light performance with excellent durability. They can be used in the form of resins, sheets or films in accordance with the design needs of the OEMs.
Dow Corning’s silicone-based additive technology makes use of silicone elastomer additive powders, which help in achieving homogenous light dispersion. The other highlights of these additives are their cost-effectiveness, high optical performance at very low loadings, reduced impact on mechanical properties and superior diffusion across all wavelengths. The best part is, these additives go well with both polycarbonate and acrylic solutions.
