OPTICAL DESIGN FEATURE
in lighting, especially if the viewer is able to see into the fixture and see the source, either directly or indirectly. This is because there is a lot of light coming from a small area. ‘It is important,’ he said, ‘to have the capability to do photorealistic rendering and luminance plots in the optical design software, so that these visual effects can be analysed and minimalised if necessary. The spectrum of OLED sources can vary as a function of viewing angle, so it is important to be able to accurately model these effects.’
Automotive light guide designed in Synopsys’ LucidShape CAA V5-based product
“Many of the new, smaller designs are taking advantage of the benefits LEDs bring to the table, while OLEDs are showing up in display applications, adding a new option for these types of applications”
LTI Optics’ Jongewaard believes that
the specification and goal determining process should be a collaborative effort between marketing and sales, mechanical and electrical engineering and optical engineering. ‘The goals and their priority can include things like the intended application, required output, visual appearance, overall cost and any regulations the product must satisfy. ‘The optical and mechanical engineer
must work closely to negotiate space and determine how to achieve those goals in an acceptable form factor. During these steps, the optical designer considers what light source and optical techniques to use, and how those can meet all the requirements. Once the concept is well defined, the optical and mechanical engineers will settle on space and optimise the design to achieve the goals. Only then can the form be designed.’
Designing a lighting system does not come without challenges, particularly with the move towards smaller systems. ‘As lighting systems get smaller,’ Jongewaard
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continued, ‘the design of the optical elements can get more challenging and the demand for higher precision manufacturing increases.’ This means that design tools such as software and manufacturing methods must be able to meet these needs. LTI’s Photopia parametric optical design tools are designed to create reflector and lens geometry based on the desired beam angles, as well as the amount of light to be directed toward each angle in the beam.
Life in colour As well as size, colour is also a design consideration, and with colour mixing gaining popularity, creating optics that provide a uniform visual appearance and avoid markings in the beam pattern, while still maintaining as much beam control, becomes a challenge. ‘The optical software,’ said Jongewaard, ‘must therefore be capable of accurately simulating LED spectral properties and material diffusing properties to provide qualitative visual and quantitative colorimetric results for the design.’ For Synopsys’ David, freeform optical
elements offer freedom in design to achieve precise light control, innovative styling, compact system dimensions and energy efficiency. However, he said: ‘As with any type of lighting system, designers must continue to find ways to manage light extraction, defeat total internal reflection, and find the best optical materials to meet performance goals. This is the challenge.’ Jacobsen sees one hurdle of working
with LEDs for lighting applications in their ability to sometimes create harsh effects
Lightening the load
The right optical design software can play a big part. Jacobsen said: ‘With the diffusion of lighting design tasks to individuals that may have little or no experience, it is important that the software be intuitive and easy to use with a short learn curve. There should also be numerous catalogues of properties, such as material, surface, and source catalogues pre-loaded with the software. It is also important to have the ability to add new properties as required. The ability to automatically optimise a design to a given goal is very important, and the software should also have the capabilities that more advanced users may require.’ With lighting being used in new ways, such as adaptive lighting, flat panel and holograms, and new technologies like solid- state lighting and OLEDs being developed, design software also helps to allow design freedom. Jacobsen elaborated: ‘As new light sources come to market, optical design software needs to evolve to cope. Typically, this will be the ability to allow the designer to accurately model these new sources in the software. Without this capability, any resulting design may be suspect. A common way of doing this for LED sources is to use rayfiles, generally available from the LED manufacturers, including the new IES LM-25 rayfile format.’ Many of these optical design software
programs are based on 3D solid modelling, which means the user can choose to make a 3D model of the source and then apply the appropriate optical properties and, with new sources, new design forms may also become more popular, according to Jacobsen, such as TIR hybrid lenses for
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