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LPI has generated major innovations in the design of illumination optics, resulting in numerous patent applications and two patents issued, as well as two product lines now on-sale and several more coming soon. LPI's non-imaging optics expertise has been brought to bear on both incandescent and LED light sources, in automotive, commercial, and residential lighting.
Although some of the automotive designs discussed herein must for now remain customer-confidential, the following summaries highlight LPI's most significant applications:
Collimation is optically defined as producing a beam of parallel light rays. The term encompasses more than ultra-narrow laser beams, applying also to searchlights, spotlights, and many flashlights. The old-fashioned way of collimation is the parabolic reflector of a flashlight, but it is thick as it is wide, loses half the light from the bulb, and makes a very uneven beam. The LPI way is a thin plastic lens with 85% efficiency and a highly uniform beam of the narrowest possible output angle, an unprecedented ±3o, expanding only 10% of the distance projected. This is the Airgap RXI Lens, currently sold as part of the OptiLED CHIP Series Commercial Spot and Designer Display lamps in 35mm diameter size, with high-power white and colored LEDs. This series of lamps comes with miniaturized voltage-adapting power electronics inside.
Conventional flashlight lamps burn out in only a few hours, so that much longer lasting LED flashlights are becoming more popular, despite their current pricing. Instead, LPI has developed a tiny plastic lens that goes over an LED and produces the same directional output as a flashlight bulb. LED's alone only emit light into a hemisphere, while flashlight bulbs send light down as well as up. LPI's Virtual Filament is an LED substitute for the filament of a flashlight bulb, and even has a similar glass envelope around it. Unlike with an incandescent flashlight lens, however, this envelope doesn't have to hold a vacuum, since it merely protects the tiny 9mm high lens that emits light from the same height above the bulb base as the filament of an conventional flashlight bulb. Now flashlight users not only have a lifetime bulb, but one that makes more light for the same battery life. Each Virtual Filament lamp has the same shape and size as a flashlight bulb, but within the base are miniaturized power electronics that can accommodate a range of battery voltages.
The Total Internal Reflection (TIR) lens is a relative of the conventional Fresnel lens. While Fresnel lens facets just refract light the same as a thick lens, the TIR lens also has facets that bend light much more than refractive facets ever could, past 90o. The first TIR lens patent was filed twenty years ago by one of LPI's senior scientists, who applied it to the Diamond Light flashlight line, still sold at Sears. Today, LPI has patented several innovations in TIR lenses. 3.1 Off-Normal TIR Lenses LPI has applied for a patent covering the ability to use a TIR lens to form a beam that comes out of the lens at unprecedented slant angles from its outer surface. 3.1.1 Linear TIR Lens When the profile of the facets of a TIR lens form linear grooves, a linear TIR lens is formed, with a focal line rather than a focal point. Linear TIR lenses were originally developed for such line sources as fluorescent lamps, and in the longitudinal direction such a lens has a very wide pattern. When LEDs are placed on the focal line, however, an exterior set of pillow lenses can focus the light from each LED to make the longitudinal pattern as narrow as the transverse pattern of the TIR lens. Such a lens has been developed for an automotive daylight running lamp, with yellow LEDs powering a beam that horizontally exits a slanted surface. 3.1.2 Circular TIR Lens LPI has designed circular off-normal TIR lenses that emit a tight beam at 45o from its flat exit surface. Such a lens is useful for ground-covering spotlights that can be flush-mounted in building walls when uninterrupted surfaces are desired, while also offering better protection from weather and easier personnel access.. 3.2 Filled-Beam TIR Lens All injection-molded TIR lenses must have non-zero draft angles to assure mold release. Thus, the beams of TIR collimators will exhibit small dark rings that are the shadows of these draft angles. LPI has developed a slightly converging TIR lens with a slightly concave conical exit face that collimates an output beam with no such shadowing. Besides aesthetics, such a filled beam makes TIR lenses available for projection applications previously unsuitable because any shadow rings would show up in the output image.
LPI has combined the virtual filament with a customized TIR lens to provide a beam-mixing collimator for multicolor LEDs. These RGB packages can be electronically adjusted for a full color gamut, and a virtual filament is bonded to each, causing the three wavelengths to be mixed in its emission. The virtual filament is at the focal point of a TIR lens that emits a beam with the desired mixed color. LPI has just introduced a product based on an array of these lenses, shining through diffusers along the length of a high-brightness accent light. Thousands of feet have already been installed.
Since their invention decades ago, LEDs have been constantly improving in efficiency and heat-tolerance, evolving from dim indicator lamps to the high-powered illuminators of today. Even so, their use for exterior vehicular lighting requires luminaires that are compact, efficient, and cost-effective. Conventional LED optics go nowhere near the optical limits set by the laws of physics. LPI's patented designs, however, exploit these limits to achieve unprecedented efficiency and compactness. 5.1 Headlamp Only for the highest levels of lens efficiency do even these lamps have sufficient brightness to meet the demanding specifications of the automotive headlamps, which not only ask for high brightness on the precisely shaped main beam, but also for very sharp cutoffs to protect oncoming traffic from glare. LPI's advanced non-imaging optics have generated LED headlamp lenses meting all customer specifications, including power, volume, and appearance. When the customer allows this design to be publicized, it will be presented here. 5.2 Daytime Running Lamp The above-mentioned off-normal linear TIR lens has been prototyped for a yellow daylight running lamp to be installed on a slanting front surface of an automobile. Conventional illumination optics (reflectors) requires the vehicle skin to be cut for a bulky cavity. LPI's slender TIR lens, however, can be attached to a slanted vehicle front surface without any cutting. 5.3 Motorcycle Taillight Using Virtual Filament technology, LPI is currently designing replacement bulbs for taillights, as well as complete fixtures for motorcycles. More details will follow upon release of customer confidentiality. 5.4 Turn Signal LED turn signals are especially challenging to design, with their combination of high candlepower and small size. LPI recently completed thin designs for both front (yellow) and rear (red and yellow) turn signals, achieving record candlepower levels at minimal LED counts.
Recent advances in glass molding enable optical quality to be attained in headlight-sized complex pieces. LPI has prototyped three halogen-based automotive headlamp designs in glass, and all of them met their desired output pattern. These compact, efficient designs offer greatly reduced volume and power-consumption when compared with both reflector and projector designs. They will be described here when their customers permit.
Because of their greatly reduced power consumption and longer operating life, LED traffic lights have enjoyed great market penetration in the last four years, with numerous companies supplying the U.S. market. LPI is currently finishing a design for sale in Texas, where the standards require double the amount of light than elsewhere. This is because the usual traffic-light standard only requires particular candlepower values for directions below horizontal. In Texas, however, most traffic lights are cable-mounted and swing in the wind, leading the Texas standard to have the same prescribed intensity values for any angle above horizontal as for below it, doubling the required luminosity. This puts a premium on efficiency and cost-effectiveness, which LPI's design well delivers. It will be described here once customer clearance is granted.
As in traffic lights, LED exit signs have also come to prominence recently. LPI is currently has two approaches to exit-signs. One uses a single high-power LED, distributing its light evenly over the face of the sign. The other uses multiple low-cost LEDs, known as chip-on-board, that uses unlensed LEDs mounted directly on a circuit board. Both achieve the required luminance with good uniformity.
Frame projectors are lights that illuminate within the frame of a mounted photograph or painting. Most commercial versions are mere spotlights that deliver a round beam onto a rectangular target. There are a few expensive lensed versions that actually image a rectangle, but only for low slant angles, with the target squarely facing the light. Instead, LPI has designed a frame-projector lens for such high-slant situations as illuminating a wall-mounted target from a ceiling location near the wall. In spite of such unprecedented obliquity (70o off-normal), uniform illumination is achieved over a well-delimited rectangular zone. LPI plans to market a family of these lenses to museums and art shops, including a battery-operated LED version for mounting street-lamp style on the frame itself.
Many illumination needs involve producing a vertically narrow but horizontally broad pattern, like the 360o pattern of a lighthouse. Masthead navigation lights for boats and aircraft warning lights for antennas are two prominent examples of 360o lights. Bow lights for boats and wingtip lights for airplanes are examples of 180o lights. LPI has originated miniaturized TIR drum-lenses that can produce 180o or 360o patterns. Besides these vehicular applications, these powerful LED lamps are also being developed for signage, where light must be cast sideways into the sign's white-painted interior without producing hot spots with light sent directly out of the sign.
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