Patent Application
20200263858
Not Applicable.
This disclosure relates to lighting fixtures and lens members for lighting fixtures, and more particularly to LED lighting fixtures comprising a plurality of LED dies mounted on a substrate, and lens members having a plurality of optical elements that correspond with the plurality of LED dies on a substrate carrying multiple LEDs.
LED lighting fixtures are rapidly replacing incandescent, high intensity discharge, and even fluorescent lighting on account of their lower energy requirements, lighter weight and compact design, which facilitates easier installation and maintenance, and excellent lighting characteristics. Purchasers of high intensity lighting are exhibiting a preference for smaller, lighter in weight multiple LED fixtures for street lighting, parking lot lighting, billboard lighting, fuel station lighting, and similar applications. As a result, smaller LED dies are being mounted in large arrays on a relatively small substrate (e.g., 144 LEDs on a 5 inch by 5 inch substrate).
Efforts to injection mold thermoplastic lens members having a plurality of optical elements, each corresponding with one of the LEDs in the array to direct the light from the LEDs into a uniform pattern on an area targeted for illumination have not been entirely satisfactory. Specifically, it has found that it is difficult to achieve the required dimensional accuracy needed to produce individual optical elements that redirect light as needed to achieve a uniform, low-glare illumination pattern, with the defects being generally unacceptable for those optical elements that are farthest from the injection molding gate. This effect is primarily due to the difficulty of maintaining high pressures farther from the gate, and also due to a tendency for thermoplastic materials to shrink away from mold surfaces as they cool and solidify.
Other attempts to overcome this problem have involved separately molding each individual lens element and installing the lens elements on a frame. This technique can provide greater dimensional accuracy and produce excellent illumination patterns. However, the process involves several steps, greatly increasing labor, production time, and tool and machine expenses, rendering it economically impractical for many municipal, industrial and commercial applications.
The inventors considered casting or injection molding the lens member in a single shot using silicone (polysiloxane) rubber. While excellent dimensional accuracy could be obtained for each of the lens elements in the array, it was determined that the concept was impractical because of difficulty handling, positioning and attaching the silicone rubber lens member to a substrate carrying a plurality of LEDs, due to the flexibility and softness of the silicone rubber.
In certain aspects, this disclosure is directed to lens members for LED lighting fixtures that include a plurality of lens members or optical members, each corresponding to an LED mounted on a substrate. The lens member includes a planar frame having a plurality of apertures, and an optically transparent silicone rubber overmolded on a first side of the planar frame. The overmolded silicone rubber defines a plurality of optical elements, each of which is disposed with one of the apertures. Each optical element is shaped to focus or redirect light transmitted through the optical element.
In certain embodiments, the planar frame is relatively rigid or inflexible relative to the silicone rubber. Preferably, the frame has a flexural modulus of about 375,000 psi or greater.
The silicone rubber used to overmold the frame is preferably heat curable at a temperature of about 140° C. to about 170° C. to provide short cycle times. As a consequence, the frame should be capable of withstanding relatively high temperatures during the cure. Suitable frame materials include metals such as steel, aluminum, stainless steel, etc., as well as thermoplastic materials having a glass transition temperature greater than 130° C., 145° C. or 150° C.
In certain aspects or embodiments, the frame comprises a transparent or translucent thermoplastic that allows some of the light from LEDs in an illuminated lighting fixture to pass through the frame to reduce the perception of glare and spread the light more uniformly.
A suitable and preferred thermoplastic material for fabricating the frame is polycarbonate, which can be either transparent or translucent.
In accordance with certain other aspects of this disclosure, an LED lighting fixture is provided. The fixture includes a plurality of LED dies mounted on a substrate, and a lens member as described above, wherein the lens member is arranged over (overlays) the LED dies such that each optical element is positioned over a corresponding LED die.
In accordance with a further aspect of this disclosure, there is provided a process of making a lens member for an LED lighting fixture using steps of providing a planar frame having a plurality of apertures, and overmolding a first side of the planar frame with an optically transparent silicone rubber to form a plurality of optical elements, wherein each optical element is disposed within one of the apertures, and each optical element is shaped to redirect light transmitted through the optical member.
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Preferably, frame 12 is transparent or translucent to allow some light from LEDs underlying the lens member 10 to pass through the grid 18 of frame 12 that defines apertures 14. This has the effect of reducing the perception of glare. For purposes of this disclosure, we define perceived glare as the tendency for an observer to see a larger more uniform after image when the observer closes her/his eyes after looking directly at the light source, rather than a field of individual spots. Preferred thermoplastics include transparent or translucent acrylics and polycarbonates having a glass transition temperature of at least about 130° C.
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While the present invention is described herein with reference to illustrated embodiments, it should be understood that the invention is not limited hereto. Those having ordinary skill in the art and access to the teachings herein will recognize additional modifications and embodiments within the scope thereof. Therefore, the present invention is limited only by the claims attached herein.
