Albis
The aluminium-based housing back cover of a LED outdoor lamp was substituted by a thermally conductive polymer from Albis.
In the following article, experts from Albis explain how switching to plastics compounds for lighting applications can bring several benefits through reduced weight, design freedom and economic advantages.
Steinel Elektronik, the market leader in sensor-controlled lighting, was looking for a production material suitable for use in replacing the aluminum-based rear housing panel on an exterior LED light (Model XLED Home 2) with a heat-conductive plastic that would support the entire system in heat management. The decision to switch from aluminum to plastic was based in part on the greater degree of design freedom plastic offers; availability and economic considerations were factors as well.
The technology company needed a material that fulfilled high standards of quality and would meet product requirements in the best possible way, while also offering long service life and allowing the use of energy-efficient production methods.
To fit this profile of specifications, the plastic type needed to be highly heat-conductive, yet exceptionally flame-resistant and electrically insulating. The clients also wanted the new design to reduce the overall product weight significantly.
The reduced weight was greatly advantageous with regards to designing the component’s movable axes. The end product was ultimately brought to market in three different colours, so the material needed to be produced in black, white, and grey. The heat sink has deep cooling ribs, creating spaces it was impossible to coat evenly with paint. To mask these spots, the material itself was colour-matched to the paint in use. In consideration of all these parameters, the company chose an Alcom heat-conductive plastic material from Albis.
Calculations and Considerations
After selecting the production material and creating samples accordingly, the project team began by performing various calculations and conducting simulations related to heat management within the application. These analyses demonstrated the material’s exceptional heat conductivity, and the resulting superior heat distribution within the component: the material measured 1.3 W/m k in plane and 1.0 W/m k through plane. Thermal conductivity directly affects the performance of the integrated electronics—the greater the heat conductivity, the better the electronic components’ performance and durability.
Therefore, the surfaces of the heat-conductive circuit board and the heat-conductive plastic were completely connected using a heat-conductive paste in order to prevent insulating air gaps. Steinel conducted testing, measurements, and simulations in its in-house laboratories, with the assistance of Albis’ applications engineering expertise.
One additional step taken was to compare Alcom TCD PA6 5060 FR WT1299-10 (colour: white) to materials manufactured by competitors. Compared to the competition, the Alcom material scored highest in terms of processing, toughness, heat conductivity, and in terms of economic aspects, so it was selected as the material to be used in series production. The results of subsequent internal painting tests were satisfactory as well, demonstrating that paint adhered well to the material. This information was used, for one, to create the desired black and grey versions of the material after completing the necessary hazardous substance analyses (PAK category 2). For another, the painting system was adapted to optimise paint adhesion to Alcom TC. XLED Home 2-model exterior lights are currently available in black, white, and grey, and are 35 percent lighter than the version using an aluminum-based rear housing panel. Thanks to its usage of heat-conductive plastic and innovative connections among the housing modules, the manufacturers were able to guarantee impermeability in accordance with IP 54 Protection Class. The components are manufactured completely in-house, which greatly optimises the value chain. Painting the components in-house also avoided the need to match or adjust structural or colour differences in purchased components. Finally, expanding and using internal resources allows the company to react more quickly to production fluctuations.
As this project illustrates, technical plastics play a key role in the lighting industry, and are indispensable materials when it comes to manufacturing lighting components in an economically efficient way.
Light Diffusing Materials
As LEDs rapidly establish themselves as a light source, however, material requirements for high-quality lighting have changed significantly from conventional lighting techniques. Standard plastics often no longer suffice to fulfill these complex requirements, making the use of modified plastics or technical compounds essential for LED lighting applications.
Using light diffusing materials, for example, can help ensure homogeneous light diffusion, exceptional light permeability, and sharp contours on illuminated symbols. Highly reflective materials, on the other hand, make it possible to separate different light sources within a small space, helping improve system light efficiency.
As technical compound specialists, Albis Plastic offers a broad portfolio of specialty products for use in technical lighting applications. The Alcom LD (Light Diffusion), LG (Light Guiding), and LB (Light Blocking) lines, in particular, have stood the test of time on the market thanks to their exceptional aesthetic appeal as well as their excellent light diffusing, guiding, and blocking qualities.
When characterising Alcom LD and LG types’ light diffusion properties, key parameters include haze and the half-value angle. Haze refers to scattered particles refracting light as it passes through a transparent or translucent plastic. Haze is calculated as the quotient of the proportion of scattered visible light and the total transmission.
The half-value angle, meanwhile, indicates the size of a light source’s angle of radiation after passing through a transparent or translucent material; it is measured using a goniophotometer to determine the angle between the detector and the optical axis at which light power falls to 50 percent of its original value.
Studies have shown that materials with a larger half-value angle have significantly higher light diffusion. It can be preferable to use materials having a high half-value angle in systems involving low wall strength and/or short distances between LED and diffuser, in order to achieve homogeneous illumination and prevent bothersome light spots.
Generally speaking, however, it is important to mention that there are no binding regulations for determining the optical properties of plastics used in lighting applications—manufacturers are free to choose test methods they consider suitable for characterising their materials.
Different diffusion systems can be employed to give technical lighting compounds different diffusion characteristics. Alcom LG, for example, diffuses light toward the front, i.e., beams of light are refracted comparatively little when passing through the medium. These materials feature high levels of overall transmission with comparatively low half-value angles, making Alcom LG compounds excellent choices for light guide systems as well as light covers.
In one project realised in cooperation with Hedi Elektro- und Gerätebau, the goal was to create a light-diffusing cover for an power distribution station with integrated light function; the cover needed to provide homogeneous light distribution and maximum possible light efficiency. The goal was an end product that gave users non-blinding light as they worked.
The company initially considered using a PMMA, but it failed to fulfill the impact resistance requirements as demonstrated in a falling ball test as per DIN EN 60598-1 Point 4.13.4 a (Lights for use in rough conditions).
After that, samples were created using two varieties of Alcom, Albis’ in-house brand: Alcom LD (Light Diffusion) and Alcom LG (Light Guiding). The material ultimately chosen was the polycarbonate-based Alcom PC 740/4 UV CC1323-08 LG. The selected compound fulfilled all requirements for series production, offering significantly higher impact resistance compared to the PMMA as well as greater light efficiency with more homogeneous light diffusion. Albis provided the project with the necessary applications engineering consultation when it came to designing the LED station cover. The screw dome area, in particular, gave Albis an opportunity to put its design support expertise to the test.
Alcom LD materials offer even greater levels of light diffusion than do Alcom LG products. They are useful in, for example, backlit components requiring maximum homogeneity in light diffusion due to low wall strength or short distances between LEDs and diffusers.
Combining the two diffusion systems allows users to draw upon the advantages of both product families, resulting in materials offering both high light permeability and high levels of scattering.
Light Blocking Materials
Inotec Sicherheitstechnik, on the other hand, needed a plastic compound suitable for use in manufacturing an LED safety light for places requiring spotlighting as per DIN EN 1838 (emergency lighting).
The component’s specification sheet required excellent light insulation as well as a self-extinguishing housing material in accordance with UL94 V-0. The component also needed to be highly UV resistance and pass the required GWFI (Glow Wire Flammability Test) at 850°C.
the company intended to use a white, flame-resistant polycarbonate. However, initial tests showed that the material did not provide the necessary light blocking, meaning that an additional component would be necessary to shield the light source. To avoid the expenses involved in additional component design and installation work, Inotec elected to use the opaque ALCOM PC 740/40 FR UV WT1182-10LB. The material is characterised by excellent flame resistance (corresponding to UL94-V-0 at 1.5 mm), a 92 percent reflection coefficient, and light permeability of just 0.3 percent with wall thickness of 0.5 mm.
These application examples demonstrate the variety and complexity of requirements involved when selecting a suitable material for use in LED light applications. Optical characteristics like transparency, light diffusion and half-value angle must be considered along with requirements regarding temperature resistance, flame resistance, the Glow Wire Flammability Test, and mechanical properties. Standard materials are often incapable of providing this wide range of properties, making it necessary to develop functional materials especially for those requirements. Albis has many years of experience with developing customer-specific specialty products for the lighting industry. Its portfolio includes a wide variety of technical compounds fulfilling technically relevant specifications. The company’s spectrum of services always goes beyond pure material selection: it offers comprehensive consultation that includes technical support throughout the entire project.
With thanks to the authors: Joachim Bernhard, Director Global Marketing E&E; Thies Wrobel, Product Specialist Alcom and Tedur Business Line Specialties; and Timm Randewig, Technical Service & Application Development (TSAD) at Albis Plastic.