Patent Application
20160025905
1. Field of Invention
This disclosure relates to diffusion coatings for lenses for lighting applications, particularly LED-based light assemblies, and lighting fixtures including the same.
2. Description of the Related Art
Light emitting diodes (LEDs) consume considerably less power than incandescent light bulbs, making them desirable replacement in the effort to increase efficiency and conserve energy consumption. To increase the luminosity of LEDs, lenses are placed in front of them, which focuses the light into a beam that is essentially perpendicular to the LED junction base. Inevitably, light dispersion from the LED is decreased, which limited the use of LEDs to specialized illumination applications until recent improvements in LED light diffusion/dispersion permitted them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. The light distribution characteristic of LEDs is significantly different from that of a traditional incandescent or wire filament-based light fixture. LEDs used in lighting fixtures do not emit light in all directions, i.e., 360 degrees. A flat-surface uncoated LED semiconductor chip will, as noted above, emit light only perpendicular to the semiconductor's surface, and a few degrees to the side. Thus the light cone emitted from an LED is relatively narrow compared to traditional light fixtures.
To increase the irradiation angle of LED light fixtures, diffusion lenses have been utilized, including that disclosed in U.S. Pat. No. 6,361,192 to Fussell et al. and U.S. Pat. No. 8,641,231, to Ariyoshi et al. These diffusion lenses of the prior art have drawbacks, however, including light transmission loss, high cost of materials, manufacturing complexities and limited diffusion performance.
Coatings that are diffusely effective rather than transmissive, have been developed for LED lighting applications in order to avoid light loss by absorption into lighting fixture cavities. These include polyurethane diffusion coatings as disclosed in commonly owned patents issued as, U.S. Pat. Nos. 8,734,940; 8,517,570; and 8,361,611, each of which is expressly incorporated herein by reference. These diffuse reflective coatings, however, are engineered to maximize the reflection, i.e., bounce back of light, into the direction and area of desired illumination, not to allow for the transmission, i.e., penetration, of light through the coating, albeit in a diffuse, i.e., less concentrated, light pattern.
A need therefore exists for a relatively inexpensive composite material that is relatively inexpensive to manufacture and apply and that is highly diffuse and thermodynamically resilient and stable, but also maintains high transmission when operating as a lens in an LED light fixture.
It would be desirable to have a simple, economical means to provide diffusive transmission of concentrated light through a lens or other form of diffuser film surface near a lighting application, which would avoid the problems inherent in know light diffusers, particularly cost of materials and complexity to manufacture and the loss of light associated with conventional diffuser technology.
In one aspect, a low refractive index polyurethane diffusion coating is disclosed that incorporates fluoroelastomer encapsulated glass bubbles or hollow microspheres, which form a highly diffuse, thermodynamically stable composite material that maintains high transmission capability when applied to a lighting fixture lens, particularly an LED fixture.
According to one preferred embodiment of the present invention, a highly light transmissive, thermodynamically stable polyurethane coating was created by incorporating hollow glass bubbles or microspheres encapsulated by fluoropolymer, particularly fluoroelastomer. The polyurethane and coated bubbles mixture is then applied to a lens surface near an LED lighting source. The resultant lens coatings demonstrated high diffusion properties for the composite material while maintaining high light transmission values when function in conjunction with an LED light fixture with a glass or acrylic lens surface.
Two polyurethane dispersion coatings to be applied to the lens surface were created. The first dispersion coating consisted of a polyurethane and glass bubble mixture, referred to in the tables and figures that follow as “C19 HD” or “HD baseline”. The second dispersion coating was a mixture of polyurethane, glass bubbles and fluoropolymer (“FP”), and is referred to in the tables and figures that follow as “C19 HDv2” or as the “fluoroelastomer” coat. For both dispersion coatings, glass bubbles with a median diameter 15 microns were used. For the second, or C19 HDv2, dispersion coating, the fluoropolymer coat weight was calculated using the volume of the average sized glass bubble and densities of the fluoropolymer and glass bubbles. A preferred fluoropolymer is a fluoroelastomer by DuPont called Viton 200GS. This fluoropolymer was suspended in acetone at 2% weight.
A calculated coat weight of 2% fluoropolymer solution was added to solution of the acetone/glass bubbles mixture and the acetone was allowed to evaporate while mixing in order to allow the fluoropolymer to remain coated to the glass bubbles. Water was added during evaporation to maintain fluidity of the glass bubble solution and to prevent conglomeration of the fluoropolymer coated bubbles. Because the fluoropolymer is insoluble in water, it remains coated to the glass bubbles as the acetone evaporates. The total coating was then mixed.
The concentrations of bubbles in the mixtures were the same for both types of dispersion coatings. Upon observation under a microscope of both the HD baseline (C19 HD) and fluoropolymer (C19 HDv2) dispersion coatings, a slight blur to the edges of the glass bubbles was observed in the fluoropolymer (C19 HDv2) dispersion coating mixture.
The dispersion coatings were sprayed onto glass or acrylic lens surfaces for light transmission and diffusion analysis. Thickness was measured by caliper versus pre-sprayed part when reported. All tests were performed with a Sylvania RT4 9 W downlight and acrylic and glass lenses cut to size. Diffusion was measured through a brightness analyzer. The most ideal diffuse surface would emit the same intensity of light across the entire surface area. The wider the center peak, the more diffuse the surface.
The light output or light intensity through the dispersion coated lenses was measured in two similar ways: (i) “White Room” and (ii) “Globe”. In the “White Room” measurement technique, the room is covered in 98% reflective material and an optical sensor is place on one wall covered with 98% reflective baffle, so as to prevent direct light and only detect reflected light. A downlight is set on the floor facing up. Luminous output is measured by sensor over time. Downlight decreases output as heat is generated, so values are recorded after output has become level. The leveling of light output over time is in
In the “Globe” technique, a hollow, plastic sphere is used. The sphere is a three feet in diameter and is coating with a WhiteOptics C18 95+% reflective coating and a 97% reflective baffle. Downlight is set into hole at top of globe. A light meter then detects luminous flux at the hole in the globe behind baffle.
As illustrated by the graph in
As noted above, ideal diffusion would emit the same intensity of light across the entire surface area. This would result in a horizontal straight line as its diffusion profile as compared to the other, non-ideal, diffusion profiles shown in
As is notable from Table 2, less light output loss was observed (at least 2.5% less) for the light passing through the fluoropolymer coating sprayed on the glass lens to an equal diffusion level (
While the foregoing has been described in sonic detail for purposes of clarity and understanding, it will be appreciated by one skilled in the art from a reading of this disclosure that various changes in form and detail can be made without departing from the true scope of the invention and appended claims. All patents and publications cited herein are entirely incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62011901 | Jun 2014 | US |
