Illumination – Plural light sources – Particular wavelength
Reexamination Certificate
2000-06-26
2003-02-25
Sember, Thomas M. (Department: 2875)
Illumination
Plural light sources
Particular wavelength
C362S497000, C362S800000, C362S545000
Reexamination Certificate
active
06523976
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an illuminator assembly incorporating light emitting diodes, and more particularly to vehicular, portable, and other specialty white-light illumination systems utilizing light emitting diodes having complementary hues.
Due to limitations in human vision in low light level environments, white-light illuminator systems have long been used to produce artificial illumination and enhance visibility during nighttime or overcast conditions or within interior quarters obscured from the reach of solar illumination. Illuminators are therefore generally designed to mimic or reproduce daytime lighting conditions, to the extent possible, so that illuminated subjects of interest are bright enough to be seen and have sufficient visual qualities such as color and contrast to be readily identifiable.
A diversity of illuminator systems such as stationary lamps in buildings, portable flashlights, and vehicular headlamps and courtesy lights have evolved throughout history and have traditionally produced white light for general, spot, or flood illumination, using a variety of sources such as candles, oil, kerosene, and gas burning elements, incandescent and halogen bulbs, and fluorescent and other arc-discharge lamps. White light is critical in such uses because of its unique ability to properly render colored objects or printed images relative to one another and its similarly unique ability to preserve luminance and color contrast between adjacent objects or printed images having different colors. For instance, a blue photographic image of an ocean panorama will be readily distinguished by an unaided observer from black photographic images of volcanic rocks when the photograph containing these images is illuminated by white light. The two images would be, however, virtually indistinguishable from one another if illuminated with a deeply red colored illuminator. Another example arises from the need to properly identify differently colored regions on conventional aeronautical or automotive maps. On an automotive map, white-light illuminators make it easy to discern the difference between the yellow markings for urban regions and the surrounding white rural areas. A deeply yellow colored illuminator would make this distinction virtually impossible. On an aeronautical chart, white-light illuminators make it possible to discern the difference between the characteristic blue markings for certain types of controlled airspace and the green pattern of underlying terrain, whereas a deeply red colored illuminator would make this distinction virtually impossible.
Furthermore, these issues of color discrimination and contrast go beyond the simple need for accurate identification. It is, for example, a well-known fact that high contrast is critical for avoiding severe operator eye fatigue and discomfort during prolonged visual tasks, whether the subject of study is a book, magazine, newspaper or a map. White-light illuminators provide more universally high contrast and good color discrimination, thereby avoiding these annoying and dangerous physiological side effects.
The extensive evolution and widespread use of white-light illuminators, along with rapidly advancing technology and a phenomenon known as “color constancy,” have fostered acceptance of a rather broad range of unsaturated colors as “white.” Color constancy refers to the well-known fact that the level and color of slightly unsaturated or near-white illumination over an area can vary moderately without substantially altering the perceived colors of objects in that setting relative to one another. An example of this is the appearance of an outdoor scene to an observer wearing slightly amber or green sunglasses. After a brief moment of adaptation upon donning the sunglasses, an observer becomes unaware that the scene is being passed through a slightly colored filter. Another example is the tacit acceptance of a wide variety of “white” illuminators in residential, commercial, and public illumination. The bluish or cool white from various fluorescent lamps is virtually universal in office buildings, whereas the yellowish or warm white of incandescent lamps is dominant in residential lighting. The brilliant bluish-white of mercury vapor and metal halide lamps is commonplace in factory assembly lines, whereas the bronze-white emission of the high-pressure sodium lamp dominates highway overhead lighting in urban areas. Despite the discernible tint of each of these sources which would be evident if they were compared side by side, they are generally accepted as white illuminators because their emissions are close enough to an unsaturated white to substantially preserve relative color constancy in the objects they illuminate. In other words, they render objects in a manner that is relatively faithful to their apparent “true” colors under conditions of natural illumination.
There are limits to the adaptability of human color vision, however, and color constancy does not hold if highly chromatic illuminators are used or if the white illumination observed in a setting is altered by a strongly colored filter. A good example of this limitation can be experienced by peering through a deeply colored pair of novelty sunglasses. If these glasses are red, for instance, then it will be nearly impossible to discern a line of red ink on white paper, even though the line would stand out quite plainly in normal room illumination if the glasses are removed. Another illustration of this effect is the low-pressure sodium lamp used for certain outdoor urban illumination tasks. This type of lamp emits a highly saturated yellow light which makes detection and or identification of certain objects or printed images very difficult if not impossible, and, consequently their commercial use has been very limited. As will be discussed later, a similar problem arises from prior-art attempts to use high intensity red or amber light emitting diodes (LEDs) as illuminators since they, like the low-pressure sodium lamp, emit narrow-band radiation without regard for rendering quality.
In order to improve the effectiveness of white-light illumination systems, various support structures are typically employed to contain the assembly and provide energy or fuel to the incorporated light source therein. Furthermore, these systems typically incorporate an assortment of optical components to direct, project, intensify, filter, or diffuse the light they produce. A modern vehicle headlamp assembly, for instance, commonly includes sealed electrical connectors, sophisticated injection-molded lenses, and molded metal-coated reflectors which work in concert to collimate and distribute white light from an incandescent, halogen, or arc-discharge source. A backlight illuminator for an instrument panel in a vehicle or control booth typically contains elaborate light pipes or guides, light diffusers, and extractors.
Of course, traditional white-light sources, which generate light directly by fuel combustion, are no longer suitable for most vehicular, watercraft, aircraft, and portable and certain other applications where an open flame is unsafe or undesirable. These therefore have been almost universally superseded by electrically powered, white-light sources. Furthermore, many modern electric light sources are relatively inefficient, e.g., conventional tungsten incandescent lamps, or require high voltages to operate, e.g., fluorescent and gas discharge lamps, and therefore are not optimal for vehicular, portable, and other unique illuminators used where only limited power is available, only low voltage is available, or where high voltage is unacceptable for safety reasons.
Because no viable alternatives have been available, however, illuminators for these overland vehicles, watercraft, aircraft, and the other fields mentioned have used low-voltage incandescent white-light illuminators for quite some time to assist their operators, occupants, or other observers in low light level situations. In automobiles, trucks, vans and the like, white-light ill
Knapp Robert C.
Roberts John K.
Turnbull Robert R.
Gentex Corporation
Price Heneveld Cooper DeWitt & Litton
Rees Brian J.
Sember Thomas M.
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