DISRUPTIVE SOLAR ENERGY & LIGHTING INNOVATIONS
Ultra-wide Angle Light Diffuser Employing a Reflective Grid
Optical diffusers are commonly employed in lighting fixtures and skylights to "soften" the light beam, reduce hot spots and improve light distribution. While there is a large variety of different diffuser designs, it has proven difficult to provide a wide angular spread for the diffused light and yet maintain decent optical transmission for the diffuser sheet. For example, diffusers with angular spread significantly reduce useful light output. Conversely, diffusers having relatively high transmission spread light within a limited angular cone and fail to sufficiently homogenize the light beam. The problem can be especially acute in LED luminaires and shaftless skylights. LEDs represent extremely compact and bright light sources which require diffusers with high hiding power to reduce their visibility and blinding glare. In skylit rooms, low-elevation sunlight tends to over-illuminate one corner of the room while leaving the opposite corner relatively dark.
Researchers at Lucent Optics have invented an advanced sheet-form diffuser which provides a very broad angular spread while preserving the optical transmittance of an optically clear material. The diffuser features a perpendicular grid of deep and narrow channels which reflect off-axis light with high efficiency using the total internal reflection (TIR).
The diffuser can be made in the form of a rigid sheet or a flexible film using any optically clear or translucent material. When using Poly(methyl methacrylate) as the substrate material, the TIR channels can be made using a CO2 laser. Laser cutting normally provides highly polished edges for the cuts and requires no further processing. Suitable fabrication techniques may also include micro and nano-embossing, molding or etching.
The diffuser is especially effective at high incidence angles at which the incident light is partially transmitted and partially redirected at a bend angle being twice the angle of incidence, thus resulting in a symmetrical diffuse light distribution with a broad angular spread. By varying the depth and spacing of the channels, the relative energy in the transmitted and redirected beam can be customised according to the lighting requirements. By making the channels sufficiently deep and causing multiple light ray bouncing from the TIR channels, the emergence angle from the diffuser can be randomized through a kaleidoscopic effect, thus even further enhancing the light diffusing and color-mixing effects. Light diffusion can also be augmented by adding various types of surface texture to either surface of the diffuser.
In LED luminaires, the diffuser can help reduce glare by "hiding" individual LEDs while preserving the light output and energy saving effect of the LED technology. The kaleidoscopic function of the diffuser may also be complemented by applying any type of conventional light-softening texture to either one or both surfaces of the diffuser.
In skylights, the diffuser can help spread daylight more evenly throughout the space even at low solar elevations (e.g., in morning/evening hours or in winter time). As a result, fewer skylights may be needed to adequately illuminate a given area. Furthermore, the diffuser can be designed to have a similar light-redistributing effect to mirrored skylight wells or shafts. The need of such light wells can be eliminated thus saving the costs and reducing the bulkiness of top-lighting products.
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