Polycarbonate: A Preferred Material Choice for LED Lighting Applications
By William Marshall, Sr. Account Manager LED Lighting, Styron, Berwyn, Pa.
Introduction
Light Emitting Diodes (LEDs) have clearly emerged as the premier choice in lighting solutions.
Government regulations and consumer preference for more environmentally conscious, energy efficient
products have caused manufacturers to develop solutions for the marketplace that offer new levels of
energy efficiency, durability and long life.
While the technology has evolved, so have the materials that go into the finished product. Plastic –
especially polycarbonate – has become the “material of choice” because of its one-of-a-kind properties
and the versatility it provides.
The needs of manufacturers and fabricators for LED lighting components are extremely complex and
typically include a variety of considerations such as:
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Protecting the costly LED light source
Ensuring top notch ignition resistance
Providing for long term heat stability
Meeting industry regulations and standards
Accommodating movement and jarring
Balancing clarity and diffusion
Meeting thermal requirements
Offering great design freedom and light weighting of parts
Very few materials can fulfill these needs. Polycarbonate and various polycarbonate blends are now
seen in a variety of LED applications because they have the balance of properties to meet these
demanding and varied requirements. This white paper discusses the components and modules of LED
lighting applications that utilize these materials as well as important considerations when selecting a
plastic resin. It focuses on the benefits of polycarbonate and polycarbonate compounds and blends and
why manufacturers and molders alike consider the material to be an ideal choice to use in LED lighting.
Components, Modules & Key Properties
One can find plastics in virtually all areas of LED applications. The three areas where plastic resins are
especially well suited include:
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Coverings, the lenses, optics, light pipes, diffusers, signage, and recessed troffer lighting
Housings and Enclosures, which include luminaires
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LED Reflectors, the parts made of high reflectivity materials that are designed to maximize light
output by directing the light emitted from an LED light source
These components all have very specific performance requirements ranging from maximizing light
output to support high efficacy, providing excellent LED light hiding capabilities and uniform diffusion,
offering superior ignition resistance to meet demanding UL requirements, and ensuring premium
aesthetics. Polycarbonate is often considered an ideal starting point. It has the basic properties needed
in LED applications and successfully can be customized to meet very specific performance requirements.
Some of the important properties which polycarbonate offers include:
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Durability
Durability is the starting point for LED light source protection. What is needed is a material that is
extremely tough. Since the LED light source itself, a solid-state semiconductor, is more robust than
traditional incandescent light sources, the materials used to cover the source should be at least as
resilient as the light source itself.
Polycarbonate is much more impact resistant and is less prone to breakage than other available
materials. It has outstanding toughness, even over a wide temperature range. Polycarbonate, which is
often used for items such as riot shields, aircraft canopies, and impact resistant panels, can withstand
tremendous impact.
Due to this outstanding toughness, polycarbonate is easier to work with and less prone to breakage or
chipping when cutting the material into shapes. In many applications, it is possible to down-gauge or
decrease the thickness of a fabricated part when using polycarbonate versus another material. This
results in part-weight and material-cost reductions, which offer a more environmentally-friendly
solution due to the fact that less product is being used and a reduced amount of energy is needed.
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Optical properties
An LED can be a very bright, unidirectional source, and manufacturers need materials that either make it
possible for the light to shine directly through a surface for maximum brightness, or provide uniform
light distribution with no evidence of the light source, for a more diffused effect. It often is a careful
balance to adjust properties, because material additives for light diffusion can impact light transmission,
and vice versa.
The covering of an LED source regulates the amount of light that is transmitted or diffused. Customers
look for a material that offers high clarity and high purity to ensure the optimum light transmission
possible. Depending on the application, manufacturers are also concerned with the uniformity of light
distribution.
Polycarbonate can be tailored to specific needs for an application through the compounding process.
Light transmission greater than 90 percent can be achieved for transparent polycarbonate resins. For
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polycarbonate resins containing a light diffusion additive, excellent light uniformity can be achieved over
the entire surface of the part while hiding the bright LED light source, eliminating “hot spots.”
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UV Stability
Exposure to a light source has the potential to compromise the properties of a material. In an LED
environment this exposure can come from two directions -- the LED source itself, and also from the
natural light of the sun. It should be noted that for LED white light sources, typically a blue LED coated
with a yellow phosphor is used which results in the emission of white light. LED sources of this nature
have little or no UV emission. Compared to traditional light sources such as fluorescents, incandescent,
HID, the LED source causes much less UV degradation of plastics materials used as lenses. The major
concern with UV exposure for LED applications is in outdoor use when exposed to sunlight. This constant
exposure can result in degradation of properties over time. This makes it especially important to select
the right material for LED applications, and when formulating materials, to properly UV stabilize the
product to minimize the impact of this phenomenon.
Polycarbonate offers a number of methods to do this including additives and layered films in extruded
product.
Clearly the selection of a material is complex and a number of factors must be considered to ensure the
right solution for LED lighting applications. Polycarbonate, understandably, is a leading material choice
because it has effectively addressed some of the most difficult challenges of the LED lighting industry.
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Thermal Stability
Lighting applications generate heat, and the proximity of the material to the light source determines the
thermal properties needed. While LED lights are considered energy efficient, they still generate heat,
particularly for the higher powered LED light sources where operating temperatures can reach
80 – 110 degrees C. For optics and lens applications requiring close contact to the LED source, a material
with excellent thermal stability is required.
Polycarbonate resins offer superior thermal stability compared to acrylic resins and can be used for
continuous use temperatures up to 120 degrees C.
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Ignition Resistance
The requirement for ignition resistance, or flame retardancy, depends on the UL codes governing the
materials used for enclosures / lenses for the specific LED lighting application. High powered LED light
sources operate at temperatures as high as 80 – 110 degrees C. Polycarbonate resins offer superior
ignition resistance for these types of operating conditions. For lower voltage applications using Class 2
power sources requiring UL 94 HB and V-2 flammability requirements, polycarbonate, acrylics and
styrenic-based resins such as SAN can be considered as materials for lenses, covers, and optics. For more
demanding LED lighting applications where Class 1 power sources are used, the materials requirement
for optics and lenses is UL V-0 and, in some cases, UL 5VA.
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Polycarbonate is among the only transparent plastic resins that offer the light transmission, thermal
stability, and ignition resistance required for these demanding applications at a reasonable cost.
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Design Flexibility
One of the advantages of LED lighting is the freedom it offers manufacturers to be creative in their
product designs. Unlike traditional incandescent lighting, the lighting industry is no longer restricted in
aesthetic configuration. Plastics materials used for housing or covering the LED source can be formed
into countless shapes and sizes by shaping resins/materials through injection molding, injection blow
molding, profile extrusion and sheet extrusion/thermoforming processes.
Polycarbonate offers this processability option with a wide range of products available for specific
processing requirements. In addition, because of the relative strength and toughness of polycarbonate,
parts can be down-gauged for weight, energy and cost savings.
Compounds & Blends
Clearly polycarbonate is a good base. It can be combined with other monomers, polymers or additives to
achieve the proper balance of properties. A user can maintain the primary properties of the material
while customizing the formulation to exacting requirements.
As an example, various components of an LED application, particularly housings and luminaire
enclosures, require opaque materials, often with demanding UL flammability requirements. Opaque
plastics block all light from passing through them and provide an aesthetically-pleasing outer covering
for the LED light source. While polycarbonate is transparent in its natural state, it can take on an
opaque appearance when combined with various additives or another material, such as ABS. Ignition
resistant PC and PC/ABS are ideal housing materials for LED applications, capable of attaining UL 5VA
flammability ratings, providing heat resistance and offering excellent processability into complex shapes.
Another example is in the area of reflective materials. Since LED sources are unidirectional, it is
important to have a material that will direct the light emitted from the LED light source to maximize
light output and minimize light loss. Additionally reflective resins must be designed with long-term heat
performance properties to ensure product safety. Polycarbonate is an excellent material for this
purpose. Polycarbonate reflective materials can achieve greater than 96 percent reflectivity.
As always, and in summary, it is important to consider an application in its entirety while choosing
materials. Careful analysis of an application will save money in the long run. By focusing on the total
system cost, materials can be selected for specific components and modules preventing over
engineering and providing for the most cost-effective solution.
About Styron
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Styron is a leading global materials company and manufacturer of plastics, latex and rubber,
dedicated to collaborating with customers to deliver innovative and sustainable solutions.
Styron’s technology is used by customers in industries such as home appliances, automotive,
building & construction, carpet, consumer electronics, consumer goods, electrical & lighting,
medical, packaging, paper & paperboard, rubber goods and tires. Styron had approximately
USD 5.5 billion in revenue in 2012, with 20 manufacturing sites around the world, and 2100
employees. More information can be found at www.styron.com.
©2014
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