Freeform lens for an efficient wall washer

Abstract

LEDs are a promising alternative to existing illuminants for a wide range of lighting applications. Besides efficiency and high durability, the small light source dimensions compared to conventional light sources open up new possibilities in optical design. In many lighting setups, it is desired to realize a prescribed intensity distribution, for example homogeneous irradiance on a given area on a wall or floor. This can be realized using LEDs in combination with specially designed freeform lenses and/or mirrors. For high efficiency, it is necessary to collect at least 70 - 80 degrees half-angle (measured against the z axis) of the light that the LED emits into a 90 degree half-angle. This results in a lens that resembles a hemisphere. The numerical design problem thus requires a mathematical description that can handle such strongly curved surfaces with strongly varying surface slopes. Surface parametrizations with a rectangular topography, like e.g. Cartesian tensor p roduct B-splines, have severe drawbacks when handling such surfaces. We report on the use of an alternative surface approximation scheme that uses a triangular mesh. We describe an algorithm that optimizes the two surfaces of a lens for a wall washer that generates homogeneous irradiance on a wall area of 2.8 × 2.8 m2 while mounted to the ceiling. The homogeneity is better than 80% and the optical efficiency including Fresnel losses is about 85%

Designing illumination lenses and mirrors by the numerical solution of Monge–Ampère equations

“…There are also methods which are based on a problem of optimal transport which leads to Monge-Ampère-type equations, see e.g. [1,6,28]. First the ray mapping, i.e.…”

Multiple intensity distributions from a single optical element

“…The employed ray-mapping method already relies on projecting the intensity distribution of a point light source onto a virtual plane to get flux density distributions between which a mapping can be calculated. 6 To obtain a suitable target irradiance distribution for the algorithm to work with, we project a prescribed intensity distribution in the same manner as we do for the point light source. …”

Toleranced freeform optical design with extended sources using ray targeting

“…To learn more about wall washes consider research papers on effective nonimaging optics techniques to develop them, 8 products from manufacturers, 9,10 and design guidelines for them. 11 A number of baseline designs were considered: imaging approach based on a fTanθ lens, nonimaging refractive, nonimaging reflective, and one of the above with integration of a lightpipe.…”