Products, Materials + Tools | Jan 18, 2016

Wacker Launches New High-Refractive-Index Silicones for LEDs

Wacker, the Munich-based chemical company, has developed new encapsulants for light emitting diodes (LED) and optical components. The compounds are made of highly transparent silicone elastomers with a high refractive index. The products withstand high operating temperatures and strong light radiation without yellowing. That makes them ideal for manufacturing LEDs with high light efficiency. They also protect the LED chip against corrosive gases, which greatly extends the component’s service life. The silicone encapsulation compounds can be processed in industrial metering processes such as dispensing.

Lumisil® 590 and Lumisil® 591 are highly transparent, additioncuring silicone elastomers with a refractive index of 1.53, which means they rank among the high-refractive-index (HRI) encapsulants. Such grades are particularly suitable for manufacturing highly efficient LEDs. The HRI silicone protects the sensitive LED chip against mechanical influences and corrosive gases. At the same time, the silicone’s high refractive index enables optimum light efficiency.

Semiconductor chips used to generate light in LEDs have a high refractive index. To maximize the amount of light emitted by the LED chip that can pass through the encapsulation, the refractive index of the chip and encapsulant must be roughly the same value. Thanks to their refractive index of 1.53, Lumisil® 590 and Lumisil® 591 make LEDs highly efficient. What’s more, the highly transparent silicones are almost completely transparent for light in the visible spectral range (approx. 400 to 700 nm) and do not yellow even when radiation is extremely intense. Transmission tests with Lumisil® 590 show that a one-millimeter-thick layer lets over 91 percent of visible light through.

Lumisil® 590 and Lumisil® 591 protect the LED chip reliably against environmental influences. Corrosive gases such as hydrogen sulfide can damage the LED chip and reduce its performance. Tests show that LED chips encapsulated with Lumisil® 590 and Lumisil® 591 are protected against such damage longer and have a prolonged service life.

The new HRI silicones are easy to process, heat-resistant and absolutely tack-free after curing. They also exhibit optimized flow and crosslinking characteristics. With a viscosity of the mix of 2,000 and 2,500 mPa*s respectively, they enable efficient, cost-effective processing. Both products are suitable for encapsulating the LED chip via contact-free dispensing processes. Lumisil® 590 and Lumisil® 591 form cured rubber grades of varying hardness. With a hardness of Shore A 65, Lumisil® 590 is relatively soft, whereas Lumisil® 591 is formulated to be significantly harder at Shore D 40.


The Lumisil® product line comprises optical high-performance silicones for LED manufacturers with high requirements. All Lumisil® products enable very efficient, cost-effective production and exhibit optimized flow and crosslinking characteristics, as well as high photostability. As an encapsulation material, they protect the LED chip reliably against environmental influences and thereby extend its service life.

Wacker offers highly transparent silicone elastomers for applications with a high (HRI) and normal (NRI) refractive index. HRI silicones combine high light efficiency with low gas permeability, which make them ideal for high-end LEDs. For NRI applications, Wacker offers a wide range of products with easy workability in conventional processes such as encapsulation, mold-making and injection molding.

About Wacker:

Wacker is a globally-active chemical company with some 16,700 employees and annual sales of around €4.83 billion (2014). Wacker has a global network of 25 production sites, 21 technical competence centers and 48 sales offices.
Wacker Silicones: Silicone fluids, emulsions, rubber and resins; silanes; pyrogenic silicas; thermoplastic silicone elastomers.
Wacker Polymers: Polyvinyl acetates and vinyl acetate copolymers in the form of dispersible polymer powders, dispersions, solid resins and solutions used as binders for construction chemicals, paints and coatings, adhesives, plasters, textiles and nonwovens, as well as for polymeric materials based on renewable resources.
Wacker Biosolutions: Biotech products such as cyclodextrins, cysteine and biologics, as well as fine chemicals and PVAc solid resins.
Wacker Polysilicones: Polysilicon for the semiconductor and photovoltaic industries Siltronic Hyperpure silicon wafers and monocrystals for semiconductor components.