FEATURE OPTICAL MODELLING
Designing an illumination system with LEDs within Photonic Engineering’s FRED software. The colour of the light can be simulated to ensure it will be attractive to the human eye ➤
user, this process is not instantaneous. ‘The Holy Grail that everybody is looking for is the ability to do the calculations in real time,’ explained Pfisterer. ‘So, the user turns the LEDs on, in the software, and then immediately you can see all the room lit up. If you could rotate the mouse and watch the light change, it would be exciting − doing that right now would take days.’ A real-time capability would allow for faster
product design and therefore a shortened time to market. ‘I think the biggest trend is getting designs out faster − time to market is important, so the faster you can get your design done the better,’ said Synopsys’ Cassarly. To advance the software to the point where this
can be realised, the processing power needs to increase to reduce the calculation time. Zemax’s Nicholson says: ‘Processing power has had a huge effect on the industry. In 20 years of selling Zemax [software] we have seen ray tracing speeds going from tens of ray surfaces per second, up to hundreds of millions of rays per second. Optical and illumination design has really been enabled by the sheer horsepower that computers bring.’ And, compared to other fields which use the freeform software, such as imaging, the power of the computer is particularly important for lighting design: ‘In illumination, it is always many millions of rays being traced in order to get highly accurate results,’ he added. ‘You need the horsepower to be able to blast as many of these rays through the system as possible.’
20 ELECTRO OPTICS l APRIL 2014
Software companies are starting to take advantage of computational ‘accelerators’ – graphics processing units (GPU) – whereby both GPUs and CPUs are used to increase calculation speed. However, to use GPUs effectively requires writing programs differently, so the software has to be rewritten. Nonetheless the advantages of faster speeds will prompt companies to modify their software so as to be compatible with GPUs in coming years, according to Pfisterer: ‘One of the things you’re going to see in the next couple of years is analysis software moving onto the GPUs to take advantage of their speed. The GPUs are exciting, because you can buy boards with thousands [of cores] on one board, and the idea of doing calculations
on thousands of these simultaneously is tremendously exciting from an illumination standpoint.’
Massively parallel computing, where several computers are used in parallel, is another approach that can be used to increase the speed of ray-tracing calculations. However, this method is not deemed as practical, according to Pfisterer: ‘Some companies are looking at massive distributed computing, but I think the technology that will win is the GPUs because virtually everyone has them on their laptops right
A real-time capability would allow for faster product design and therefore a shortened time to market
now, they are affordable, and they are very fast.’ A current solution that addresses the issue of speed for optimisation is a programme from Zemax, OpticStudio 14, for engineers wanting to visualise an illumination system before they commit to its full design. The software carries out estimated ray trace calculations to give designers an initial idea whether it’s worth going further with the design process. ‘We have just introduced LightningTrace, which makes a lot of illumination design interactive,’ said Nicholson. ‘So, you can sit at the computer and use slider tools to adjust system variables, and the whole illumination factor changes before your eyes − and that helps you get into the ballpark of a good design. Then, you can
switch over to the conventional ray-trace, where you need to trace millions of rays and get really accurate results.’ Although processing power is a major factor, to
really allow for developments in the software and make the design process faster, standardisation is key, according to Pfisterer: ‘International committees are trying to develop standards for passing characterisation data back and forth between software products. And, there is a lot of work being done so that vendors who make LEDs can create common formats that anybody’s
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Photon Engineering
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