Facet Lens Technology
The answer to overcoming the bottlenecks in conventional optics design methodologies is to apply modern mathematical methods from physics and computer programming to generate the required optics, leading the focus away from ‘how to achieve it?’ towards ‘where is the light desired?’ Here’s a brief explanation on how ‘Facet Lens Technology’ works.
Complexity is Free
Traditionally, methods of optics design has included ray-tracing, combined with human expertise to optimize parameters of the design. This approach often entails manually finding the best optical design for a certain problem, relying on the expert’s insight to foresee the direction in which the optimal solution can be found. Basically, this reliance on expertise and foresight is a consequence of the ray-tracing method utilized in most optics design programs.
While the ray-tracing method is very reliable, it works in a straightforward manner. It begins at the light source in order to arrive at the target: the external distribution of light, often stored as a Eulumdat file or a ray-file. The optical design here is ‘input’, whereas the target distribution is ‘output’. An important consequence of this source-to-target method is that a complex target distribution requires the optical designer to input an optical design with similar complexity in order to control the light well. One can imagine that this becomes arduous if a large amount of complexity is required.
Applying the target-to-source method of calculating optical design, in this case, the output is the optical design in a digital format, whereas the inputs are the light source properties and the requested external distribution of light. While there is a mathematically infinite set of optical solutions that provide the requested distribution given the light source, modern optimization algorithms can cut through the proverbial fog to provide the most practical designs. An important consequence of this method is that at least the same level of complexity is transferred from the requested distribution of light to the optical design.
Image Faceted Lens
The first application of this technology is through the programmatic generation of faceted lens designs. A faceted lens consists of many similar-sized facets that “cut up” the light from the source. Each facet then aims the narrow bundle of light passing through it in a specific direction, such that all the beams from all the facets together make the requested external distribution of light. It does not matter whether that goal is a simple spotlight, or two spotlights, or something as complex as a logo. The complexity of the optical design stays the same, and often a single optical element is enough.
‘Sunflower Fresnel’ – a multi-facet lens precisely directing light to the illumination target
Faceted Lens Image Bundles
A lens of 50mm diameter with 4mm² facets has approximately 500 facets. If an LED with a light emitting surface of length 2.4mm is placed 25mm behind the lens, each of the 500 beams has a (FWHM) opening angle of 5-10°. This spread in opening angles can be used to optimize the distribution of light, or eliminated by changing the relative size of the facets. The beams could be made even narrower by using a smaller LED source at a larger distance with a practical limit of about 2°, though placing the LED closer to the lens also reduces the size of the outer beams while at the same time increasing the size of the middle beams. It depends on the application what is preferable.
One advantage of having a relatively large lens surface, is that it is possible to reduce glare. Depending on the target distribution, facets on different areas of the lens can aim in similar directions. For someone looking into the light, the LED’s sharp point of light is now spread over multiple points in different areas of the lens. This has the added benefit that it reduces the sensitivity to fouling by environmental effects, and redundancy in the case of partial obstruction.
The target-to-source method is ideally suited to give the creativity back to the light architects, artists, and designers by providing reliable optical designs with proven quality, while being able to deliver unique designs for every assignment. By making use of additive manufacturing, every lighting project has access to optimized optical designs of the level of complexity needed.
Additive optics fabrication combined with target-to-source optical design methods open up a world of opportunities for creative lighting designers in branches as diverse as public lighting, artistry, architectural lighting, art illumination, and advertising. Because the efficiency of single element optics is naturally high compared to most other methods of beam-shaping, e.g. image projection methods and shutters, it is our expectation that faceted lenses and other target-to-source based optical designs will become the norm for the creative lighting industry.
Light, the core of our existence, can now be used in light engineering and design projects in a much more friendly, simple, effective and responsible way!