27 May Prototyping of light diffusion materials
Miguel Ángel Jiménez
Head of Prototyping Area for Andaltec
This article is intended to elaborate on the most employed techniques to transform the light produced by a certain lighting source (a bulb filament, or LED light) into a surface continuously and uniformly lit, with no other intermediate part other than the diffuser itself
This technique is not new but, since the generalisation of LED lighting, has generated a great increase of applications which intend to light a work surface or an object, with certain homogeneity in light distribution and intensity. At the same time, when the device emitting the lighting is observed, this should also present a distinctive and eye-catching look.
Diffusion light sources are excluded from this article, that’s it, those in which the surface itself is already the lighting source. This would be the case for the OLED films or pixel screens on devices such as mobile phones or the latest television sets, which achieve the same effect but at a much higher cost.
There are two types of “light diffusion techniques”: based on refraction and on diffusion (see figures)
1 REFRACTION: diffuse surface, estimated for that purpose by means of surface microstructuring
2 PARTICLE DIFFUSION: these particles are distributed homogeneously in bulk inside the material.
It is usual to find both light diffusion techniques when manufacturing lighting devices in high-volume series. The first one is achieved by replicating the microstructuring in the mould from which the diffusion part comes. The second technique is achieved in the manufacturing of the raw material chipping with which the part is made. Thus, in any of these cases, no additional filters or parts are required in order to attain the desired effect.
Regarding option number 1 (Refraction), light control is much more efficient thanks to the mathematical estimation on which this technology is based. At the same time, however, it is more complex to replicate in a part or mould, as it requires machining techniques by means of chipping removal, at high speed tool turning, and very accurate machining centres. As an alternative to machining, another option is removing the material through advanced techniques using femtosecond laser. Success is attained when a very tiny and accurate roughness is produced, known as microstructuring. Despite all of this, this technique is widely recommended within the automotive sector for road lighting devices, being in some cases the only option, since for these devices, light distribution is not homogeneously perfect for every point but random, depending on the regulation to be complied with. That is the reason why it is preferred the use of the reflection technique, as it assures a better control of light beam direction and efficient repetitiveness for serial production. You can even achieve, for dipped beam lights, that the gradient of the passage from the lit to the unlit area meets the vehicle manufacturer’s specific needs, in order to enhance driving comfort. This must always be done within the narrow range of values allowed by official regulators.
As for option number 2 (Particle diffusion), it is more random than the first technique, hence the diffusion effect. It is also repetitive in serial production, as long as validated materials are employed as diffusers, being designed specifically to achieve that effect. If we go back to the previous example for the automotive sector, this technique is more directed to signalling applications (for “being seen”, not “to see”), due to the fact that the material in suspension reduces transmittance a lot because of retroreflection and light absorption due to particles in suspension. This technique shows multiple applications in the furnishing area and interior lighting, since decoration professionals do not only intend the light from the device to illuminate the space, but it is also expected to create a certain and even customised atmosphere. The lighting device, being on or off, is expected to be part of the room’s decoration too.
All in all, the conclusion to be reached is that each technique has strong and weak points: there where the diffusion effect is mathematically accurate, the replication process for mould or part is complex; whereas for those cases where the optical estimation and manufacturing is almost trivial, the diffusion effect is very limited as for the choice in range for the desired effect, due to design constraints.
Once the optical devices are already manufactured and moulds have been designed and manufactured, usually at high cost, the manufacturer expects customer specifications to be met; otherwise, the money invested in moulds and the business opportunity will most certainly be wasted. In order to avoid this undesired situation and in order to add competitive improvement, Andaltec has developed fast prototyping techniques, both for refraction diffusion and particle diffusion. They allow for a validation of both optical function and the desired effect, all of it before proceeding with huge investments for serial production. This is achieved by machining the microstructuring directly on the part with the mathematical roughness estimated on its surface, which, once validated, would be replicated on the mould, counting with a complete success certainty. Another option consists in resins designed specifically by Andaltec. They achieve transmittance values very similar to those of the materials validated for thermoplastic injection, such as Plexiglas Satinice 8N, in its several degrees DF23 and DF21 or some Makrolon, series 2407. These resins allow for part production using alternative methods to mould injection, as it is required for validated diffusion materials
Andaltec is nowadays the only organisation in the world with capability to carry out these breakthrough prototyping techniques, following the features described in this article. As it was stated before, there is no need in any case for the manufacturing of the definitive mould, not even for soft materials like aluminium.
There are already applications in the market in which these technologies can be found. They provide eye-catching effects, having more or less aesthetic success but it is certain that new applications, still unusual currently, will be developed thanks to the freedom in aesthetic effects bestowed by industrial design. This is helped by the multiplying effect introduced by innovation in the kind of lighting sources, which adds effects such as colour, variation in light intensity and sinchronisation.
Applications for lighting: furniture, display cabinets, ambient lighting, car headlights, ceiling decoration, …
Applications for signalling:
- Home: living-room, garden, kitchen, transit areas
- Interior/outer decoration for hotels
- Compact bathrooms: shower cabins, splashing
- Traffic signs
- Automotive area: car interiors, rear lamps, …
- Public buildings: fittings, façades, information signs, …