Transforming the Solid-State Lighting Industry with Optical-Grade Silicone

Expectations are that the solid-state lighting industry will be transformed by the use of optical-grade silicone. It enables injection molding of complex optical designs, which integrate the superior properties of different plastics and glass to offer low-cost flexibility and thermal resistance, as well as brilliant light transmission.

Since cameras mandate the use of high-quality optics, lenses contribute to a significant proportion of the component costs. Complex, multi-part optical designs require the highest quality glass or other optically transparent materials. These requirements and the need for accurate design and manufacturing processes result in a significant increase in the cost of the lens.

However, despite the fact that cameras require lenses to gather and focus light onto a focal plane, they capture light emitted from different types of sources. In the case of existing industrial and architectural imaging applications, these light sources are generally high-efficiency solid-state LED lights.

Silicone Optics: Tailor-Made for LEDs

A number of advantages are provided by LEDs, such as low cost and maintenance, high efficiency, and increased spectral control. Yet, with respect to one critical aspect, solid-state emitters are similar to their incandescent ancestors: they emit light in all directions.

In September 2013, after spending two years for equipment acquisition and proving competency, Smart Vision Lights began testing its own LED products for legally applying marks of conformity, such as Europe’s CE mark, to its products.

The traditional solution for an application that requires more light is to increase the number of bulbs, which is also the same for LED lights. The drawback of this solution is the generation of increased amounts of heat and the higher power consumption, both of which are not efficient or desirable.

In contrast to LEDs, gas discharge (halogen) lamps, fluorescent lamps, and incandescent lights are significantly less efficient in terms of the conversion of electrical power into light. Yet, to achieve further improvement in the efficiency of LEDs, the lamp must have the potential to collect all of the available light and direct it to the targeted area. This aim is very important for any lighting application.

However, realizing light control is critical to the success in the machine vision world, regardless of whether it is the bright field, dark field, structured, diffuse, polarized, or some combination of any of these types of lighting systems that is generated.

Regrettably, standard glass molding and grinding methods synthesize microlenses, which are expensive than the chip. Another alternative that can be used is plastic molded optics; however, plastics are likely to turn yellow over time, particularly when they are exposed to ultraviolet (UV) light. Another challenge is that they cannot hold the fine features needed in the case of complex optical design.

Furthermore, they do not have the ability to endure high temperatures produced in lighting applications, leading to crazing (the development of microscopic cracks) and other detrimental conditions. The addition of phosphors to plastic materials to enhance the performance of plastic optical has not been so successful.

The use of silicone optics could be the solution to these challenges, and many more. Using these, end users can control light with precision, which can otherwise be realized only with the help of complex glass optics that are quite costly for most of the architectural or machine vision applications.

How are Silicones Special?

The innovative optical-grade silicones from Dow Corning are an attractive alternative that can be used by lighting manufacturers. When compared to plastics and glass, silicone:

  • does not craze due to heat, showing no material changes at temperatures ranging from –115 °C to 200 °C
  • does not turn yellow with time
  • does not react with most of the harsh chemicals
  • does not react with UV light
  • allows high transmission across a broad spectrum, with 95% or more transmission between 365 nm (UV) and 2000 nm (IR)
  • does not age like polycarb, vinyl, or acrylic

Besides these material benefits, in contrast to plastic-molded lenses, silicone also provides sophisticated manufacturing benefits as follows:

  • Silicone is very powerful and retains its optical function over its service life. It also withstands environmental changes.
  • When compared to conventional plastics, optical-grade silicones have the potential to hold fine structure patterns. They also have the ability to possess reverse curves in a single molding tool.
  • Silicone’s ability to form complex optical elements with the help of multiple shots in a single injection mold guarantees a lower total cost solution for multi-part, complex optics.

More Light, Fewer Lamps, Better Control

Silicone optics provide a number of benefits, all of which are the result of the unique properties of silicone molecules. Their spaghetti-like, long structures give rise to liquids that slowly cure into flexible solids with low refractive indices. This reduces the loss of light at the interface between optic and air, or multi-part optics.

Regardless of the fact that it retains a flexible semi-rigid shape, due to its liquid origin, it is possible to modify silicone into extremely fine structures below 10 nm to create diffractive, Fresnel, holographic, and other optical structures with reduced loss.

Furthermore, the potential of silicone to retain its flexibility for more than a year makes it is comparatively uncomplicated to blow the injection-molded optics out of the mold without affecting the fine structures. A majority of the optical materials with rubber-like characteristics do not return to their original shape upon being stretched while blowing an injection-molded part out of a mold.

When compared to glass or plastic, silicone can be molded at significantly lower temperatures. Consequently, it is possible to develop prototype molds with the help of polyethylene and polyester resins. Nearly 3000 prototype optics with enhanced repeatability can be developed using these resins.

The ability of silicone to be molded at relatively low temperatures enables other materials with low melting points—such as seals, O-rings, and snap fixtures for the attachment of the silicone lens to the LED—to be included in the mold of the optical design.

Characteristics of Silicones

Example of Applications (LED Package)

Example of Applications (Lamps)

Example of Applications (LED Luminaires)

Recently, this feature was used by optical engineers working with LED light manufacturer Smart Vision Lights (Muskegon, MI) and LumenFlow (Wyoming, MI) to create many prototypes for a five-million-lux LED linear light at a fraction of the standard tooling cost of $100,000 per mold.

Silicone and the 5M-Lux LED Light

LumenFlow was one of the first optical companies to begin working with Dow Corning to develop silicone optics for LED lights. Luckily, LumenFlow is located nearer to Smart Vision Lights, a leading LED light manufacturer. The two companies collaborated to develop the first-ever five-million-lux LED linear light.

Linear lights are increasingly used on large area production lines for the illumination of products for high-speed machine vision camera-based quality inspection systems. The camera has the potential to more quickly acquire the images of the product if the light is brighter, thereby making the production line more profitable.

Matt Pinter, the head of engineering at Smart Vision Lights, had tested the use of extruded acrylic rods to focus the light from the water-cooled LEDs. However, they would have needed a diameter of over 2 inches.

The line’s integrity was compromised also by the poor surface quality. Furthermore, the acrylic material was put to risk by high temperatures, leading to eventual crazing and misshaping as time passed.

The diameter of the silicone complex optic created by the two companies was 40 mm, and it had the potential to endure five million lux and the associated heat, while still maintaining the focus of the light line. Two back-to-back 40-mm molded large-aperture silicone lenses were included in the silicone optic.

A complex conic structure provided in each cylinder reduced the induced aberrations that generally occur in rod optics. Due to the fact that silicone is a “living material,” it was feasible to make the lenses into six-inch segments and butt them together.

The molecules simply flowed back together due to the fluidity of the material—within a short time, the difference between the optic and the joint material was not apparent. This allowed Smart Vision Lights to develop the light at a length of around 9 feet.

The back-to-back lenses allowed a larger object distance (So). This indicates that both the optics and the LEDs were subject to less heat stress. Finally, Smart Vision Lights was able to include a wire polarizer through the back-to-back placement of the lenses. This was new for LED lights of that intensity.

Conclusion

The exceptional optical properties, molecular geometry, and unique chemical composition of optical-grade silicone allow LED manufacturers to enhance the performance levels of their products like never before. They can open the door for novel applications and save a considerable amount of money for customers since they fulfill their illumination needs.

The creation of a five-million-lux linear light with superior optical performance at a fraction of the regular development costs suggests that silicone is evidently the new champion in optical materials and technology.

Thermal Stability of Silicone

200-hour thermal aging test (4 mm thickness)

200-hour thermal aging test (4 mm thickness)

Typical organic materials used for optical systems in lamps and luminaires, and silicone resin aged at 200 °C for 24 hours

Typical organic materials used for optical systems in lamps and luminaires, and silicone resin aged at 200 °C for 24 hours

Injection Molding Optical Parts—Benefits

This information has been sourced, reviewed and adapted from materials provided by Smart Vision Lights.

For more information on this source, please visit Smart Vision Lights.

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