Abstract
Glare and visual discomfort are important factors that should be taken into account in illumination design. Conventional freeform lenses offer perfect control over the outgoing intensity distribution, thereby allowing optical radiation patterns with sharp cut-offs in order to optimize the unified glare rating index. However, these freeform lenses do not offer control over the near-field luminance distribution. Observing the emitted light distribution from a high-brightness LED through a freeform lens gives a high peak luminance that can result in glare. To reduce this peak luminance, freeform lenses should be used in conjunction with light diffusing structures. However, this diminishes the control over the outgoing intensity distribution what is the main benefit of a freeform lens. Another approach to reduce the observed peak luminance, is by spreading the emitted light over multiple optical channels via freeform lens arrays. This paper proposes a novel method to design luminance spreading freeform lens arrays that offer perfect control over the resulting intensity pattern. The method is based on a non-invertible mapping of a 2D parameter space. This results in a source-target mapping in which multiple ingoing ray directions are mapped onto every position of the target distribution. The case of continuous and discontinuous mappings are both discussed in this paper. Finally, the example of a discontinuous freeform lens array with 7×7 individual lenses is designed and experimentally demonstrated.
Highlights
Visual discomfort is an important factor that should be taken into account during the design of optical components for general lighting applications
This paper proposes a novel method to design luminance spreading freeform lens arrays that offer perfect control over the resulting intensity pattern
The zero-étendue methods can be divided in three groups: ray-mapping methods [5,6,7,8,9], supporting quadrics methods [10,11,12] and Monge-Ampère methods [13,14]. All these methods make use of the assumption that every ingoing ray from a source distribution S is redirected to a unique position in the target distribution T and, vice versa, that each target position is illuminated by only one ingoing ray that is deviated by the freeform lens
Summary
Visual discomfort is an important factor that should be taken into account during the design of optical components for general lighting applications. A different method is proposed that directly constructs N × N ray mappings, starting from a single source-target mapping This initial ray mapping is transformed by means of a non-invertible fold mapping which results in multiple ray mappings from which the individual freeform lens elements can be obtained. This folding approach ensures that an array of multiple freeform lens surfaces is obtained which reshape the source distribution S into multiple overlapping beams that form together the desired target distribution T
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