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Papers

Glass light guides for color mixing of high-power LEDs

C. Paßlick ; U. Geyer ; T. Heßling ;  A. Hellwig ; M. C. Hübner

Proc. SPIE 9949, Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials 2016, 994907 (September 27, 2016); doi:10.1117/12.2236821

http://dx.doi.org/10.1117/12.2236821


Constant LED developments show increasing levels of luminous flux and power densities. In particular, automotive and entertainment industries are requesting mechanically and optically stable light guides for their new mid to highest-power lighting solutions. The switch from polymer to glass optics comes with improved temperature resistance, higher optical performance and better longevity of the systems [1, 2]. Even highest-power LEDs can be driven at maximum current obtaining best light output. The option of directly implementing micro structures on the output aperture of glass light guides gives the opportunity to customize final color mixing and light scattering over a wide range. This reduces the amount of required components and subsequently the total system costs.

 

© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Micro structured glass optics - basics and benefits

U. Geyer ; C. Paßlick ; T. Heßling ;  A. Hellwig ; M. C. Hübner

Proc. SPIE 9949, Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials 2016, 994908 (September 27, 2016); doi:10.1117/12.2236865

 

dx.doi.org/10.1117/12.2236865

 

Today’s trends in illumination engineering clearly turn towards high power LED applications with a precisely controlled light output. The first requires glass optics which will withstand the increasing temperature load and lumen output of LEDs. The second requires tight control of production tolerances and defined surface structuring. Especially the surface structure – which can be realized for example as micro lens arrays – is of increasing importance. Using two different fabrication techniques we investigated the implementation of micro surface textures on glass optics. The first method uses directly molded glass from the liquid phase while the second is an imprint process. For both methods we determined the minimum replicable feature size and found current limits of only 50 μm for the imprint process.

 

© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Sensitivity of the optical performance of LED illumination systems to manufacturing tolerances

C. Paßlick ; A. Hellwig ; U. Geyer ; T. Heßling ; M. C. Hübner

The remarkable market growth of high power LED solutions leads to a considerable demand for durable optics. Due to its superior properties glass is increasingly requested in the automotive and stage lighting industry, but also general lighting applications do benefit.

In many projects we encounter an uncertainty of customers regarding the required surface accuracy of their optics. To be on the safe side those customers specify requirements close to the technical limit, which are indeed not necessary for many applications. Subsequently, this increases total cost of ownership without any benefit for the customer.

The document discusses typical manufacturing tolerances and their consequences on the optical performance. When accounted for during the design phase, the effect of manufacturing constraints and positioning tolerances can be considerably reduced.

This is demonstrated with two examples including a freeform lens for high-bay lighting and a large-size TIR collimator for general lighting applications.

This paper was presented during 5th International LED professional Symposium +Expo (LpS 2015), Bregenz, Austria.

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Stability of glass versus plastics for transmissive high-power LED optics

C. Paßlick ; A. Hellwig ; U. Geyer ; T. Heßling ; M. C. Hübner

Proc. SPIE 9192, Current Developments in Lens Design and Optical Engineering XV, 919210 (September 25, 2014); doi:10.1117/12.2061854;

http://dx.doi.org/10.1117/12.2061854

In the past, the major part of transmissive LED optics was made from injection molded polymers like PMMA or PC. Recent LED developments now show constantly increasing levels of luminous flux and energy densities, which restrict the usability of such polymer optics due to their limitations in thermal stability. Thermal simulations have shown that light guiding/mixing structures (rods) made from polymer materials can easily reach temperatures above their melting point due to the absorption characteristics. However, there is a great demand for such light rods from the automotive and entertainment industry and thus glass is becoming increasingly important as an optical material.

Glass has typical transformation temperatures of hundreds of degrees Celsius and therefore withstands the conditions seen with LED without any problems. Square-shaped glass light guides show temperature advantages over round light rods, which are known for being able to produce caustics inside the material causing absorption and temperature hot spots, respectively.

This paper presents some comparative thermal simulations by means of the Finite Element Method for a light conductor as an example and gives corresponding assistance for an appropriate material and light guide shape selection for highpower LED optics.

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© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

Tailoring free-from glass reflectors towards a homogeneous luminance distribution in roadway applications

T. Heßling ; U. Geyer ; A. Hellwig ; C. Paßlick ; M. C. Hübner

Proc. SPIE 9191, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration XI, 919106 (September 5, 2014); doi:10.1117/12.2061810;

http://dx.doi.org/10.1117/12.2061810

Free-form reectors are encountered in numerous illumination systems, especially in highly sophisticated applications. The construction of these kind of optics however remains a challenging task where only a few methods are available to derive the free-form shape. One such method is the multi-ellipse approach where a superposition of conic sections is utilized to create the desired illuminance or luminous intensity distribution. While it is useful in many areas one is not always interested in an illuminance or intensity distribution. Especially street lighting reectors are often tailored towards a homogeneous luminance, taking into account the road's reective properties, luminaire arrangement etc. While we used our implementation of the multi-ellipse method to design street lighting reectors with a uniform illuminance before, we now extended this method to support the calculation of a roadway reector with a homogeneous luminance. For a given roadway scenario we can quickly get an optimized reector with a good performance compliant to roadway standards such as EN-13201 or IESNA-RP-8-00. Furthermore the optic can be quickly adapted to changing requirements.

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© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

Reflectors and Lenses vie for usage in SSL Systems

LED point sources have fundamentally changed the optics industry, reports Dr. Marc Hübner, and developers working on SSL systems must consider both reflectors and lenses and match designs to application at hand.

LEDs are quite different from conventional light sources in many ways including in optical behavior where legacy sources primarily emit omnidirectionally and require a reflector to shape the radiation. LED point sources radiate in one hemisphere and often require the use of collimators in the form of total internal reflection (TIR) lenses to steer the beam. But optimum solid-state lighting (SSL) product design requires an understanding of both reflectors and lenses, and we will describe the physical foundation of these optics and help guide the selection and optic design process.

Due to the typical layered structure of an LED chip and built-in primary optics in the package, the emission of light is approximately Lambertian. Sometimes this basic emission is further influenced by additional optical means that are integrated into the LED, often featuring a reduced beam angle. The challenge for the SSL developer is further control of this pre-formed emission.

This article was published in the November/December 2013 issue of the LEDs Magazine.

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Glass Optics for LED Applications

Historically seen, glass is a very old material and evolved with many different mixtures into a broad variety of applications, from objects of daily use to art objects and high end technical tools like optics. Dr. Thomas Hessling, Optical Engineer at Auer Lighting's R&D/ Lighting Technology department explains why glass is also the first coice for secondary lenses in LED systems.

In the field of illumination optics glass became invaluable with the invention of the electric light bulb. An evacuated glass housing was necessary to prevent the filament from oxidizing and glass was the material of choice. With the advance of artificial light sources to higher and higher powers glass remained the number one material due to its high temperature and mechanical stability. It easily withstands the operating temperatures of incandescent as well as even more powerful light sources and so it was also chosen as material for the primary optics such as reflectors , lenses or diffusers.

This article was published in the July/August 2012 issue of LED professional Review.

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