Semiconductor light sources, such as light emitting diodes (LEDs), provide efficient and robust full-spectrum lighting sources. LED-based luminaires or light fixtures are used for interior and exterior applications such as, for example, street lighting. In particular, chip-on-board (CoB) LED arrays provide high luminance combined with narrow-beam light generation to provide tight focusing/low geometric spreading of illumination. CoB LED arrays generally refer to one or more semiconductor chips (or “dies”) in which one or more LED junctions are fabricated and where the chip(s) is/are mounted (e.g., adhered) directly to a printed circuit board (PCB). The chip(s) is/are then wire bonded to the PCB, after which a glob of epoxy or plastic may be used to cover the chip(s) and wire connections. One or more such LED assemblies or LED packages in turn may be mounted to a common mounting board or substrate of a lighting fixture.
Optical elements or structures are used together with the CoB LED arrays to facilitate focusing of the generated light to create a narrow-beam of collimated or quasi-collimated light. These optical elements can include, for example, lenses or collimator lenses (collectively “lenses”). These structures capture and redirect light emitted by a light source, e.g. the CoB LED array, to improve its directionality.
Traditional CoB LED array based street lighting use freeform optics, as shown in FIG. 1, as the optical element or lens to disperse light onto the road in a specific pattern. The freeform optics depends on the street or road type (highway, urban, pedestrian, etc) and the regional standard that is applicable. Usually the CoB LED array has a fairly simple luminance distribution (either square, rectangular or circular), and the freeform optics is used to transform the CoB LED array luminance distribution into the specific distribution that is needed for the street. The size of the freeform optic is a function of the light source size. The larger the light source size, the larger the freeform optic size. For CoB LED array based street lighting such freeform optics become large and expensive. Given the large number of streetlight patterns, the number of freeform optics types for a luminaire supplier can become rather excessive. For CoB LED array based street lighting, which is supposed to provide a low cost solution in the market, maintaining inventory and tracking large complicated freeform optics are a market barrier.