Card – picture – or sign exhibiting – Illuminated sign – Lamp box
Reexamination Certificate
1998-06-25
2001-09-04
Jones, Deborah (Department: 1775)
Card, picture, or sign exhibiting
Illuminated sign
Lamp box
C040S541000, C362S812000, C359S599000, C428S343000, C428S458000, C428S460000, C428S461000, C428S472000
Reexamination Certificate
active
06282821
ABSTRACT:
FIELD OF INVENTION
This invention relates to diffuser films for use in the signage industry to increase lighting efficiency.
BACKGROUND OF INVENTION
Lighted signs are everywhere in modern countries. The sign can educate, entertain, inform, or warn the viewer. The sign can be designed for close or distant viewing. Lighting is provided to assure the viewer can see the message, particularly during dimly lit days or nighttime.
Lights require energy to power them. Modern countries readily can provide the power, but those who pay for the energy are always seeking more efficient delivery of the power and more efficient usage of the power. The energy required to power a lighted sign should not be wasted for economic and environmental reasons.
Lighted signs can be “front lit” or “back lit”. The former typically include such signs as billboards or other displays where the light is shone from the perimeter of the sign at an angle toward the sign. The latter typically have a translucent surface through which the light is seen and on which the message or image is placed. Uniformity of light emanating from the translucent surface is important. Often, the translucent surface includes some element that diffuses the light to reduce the identification by the viewer of the point or linear source of the light within the sign housing. Moreover, typical backlit signage today allows less than 30% of the light to escape from inside the sign for viewing. Clearly, a more efficient lighting system is needed.
The lighted sign can be in any configuration: Light sources can be neon, fluorescent, incandescent, halogen, high intensity discharge (HID), light emitting diodes (LED), or light fibers. The sign can be integral to a building, mounted as a fixture on a building, freestanding, or a part of other apparatus or equipment. The light can be powered continuously, periodically, episodically, or irregularly. Whenever the sign is lighted, the power used should not be wasted.
The lighted sign cavity can be any geometric configuration.
Lighted signs that have a perimeter shape of a complex geometry to convey the intended message are entirely different types of signs from lighted signs that rely on a Euclidean geometry with the intended message within the perimeter. In the industry, an example of the former type of sign is called “channel letters” and can generically be called “complex shape lighted signs.” The latter are called “sign cabinets” because the perimeter of the sign is irrelevant to the message being conveyed.
Nonlimiting examples of sign cabinets include rectangular, oval, circular, elliptical, and other Euclidean geometrical shapes. Nonlimiting examples of complex shape lighted signs include letters, profiles, silhouettes, characters, or any other shape desired by a customer that helps to advertise, educate, warn or the like.
Lighting of Euclidean geometric sign cabinets is more predictable than complex shape lighted signs, because even distribution of the light is quite difficult to obtain unless the light source has substantially the same shape as the viewing area of the sign.
SUMMARY OF INVENTION
What the art of lighted signage needs is a diffuser layer for use in association with the translucent surface of a lighted sign, that can improve the luminance efficiency of the lighted sign and therefore increase the brightness, reduce the power consumption or achieve a combinations of these benefits.
“Luminance efficiency” means the total flux (in lumens) exiting the translucent surface of a lighted sign cavity divided by the total flux emitted by the light source(s) within the lighted sign cavity.
One aspect of the invention is a low-loss, partially diffuse-reflective and partially diffuse-transmissive diffuser film, optionally laminated to a clear, non-diffusing substrate if necessary to provide structural integrity, for use in association with at least a portion of a translucent surface of a lighted sign cavity having interior surfaces at least as reflective as painted walls, wherein the diffuser film provides an increase in luminance efficiency of the lighted sign over a lighted sign that does not have such film applied therein.
Preferably when co-laminates are present for structural integrity, the low loss diffuser film occurs as the layer closest to the interior of the sign cabinet.
Light incident upon the diffuser film of the present invention from the interior of the lighted sign cavity is partially reflected and partially transmitted by the diffuser film. The reflected light is returned to the cavity of the lighted sign. The transmitted light passes through diffuser film and, optionally, the co-laminates of the diffuser film if present, and exits the lighted sign to the viewer without further reflection.
Luminance efficiency is provided by the diffuser film of the present invention because there is no significant absorption of light as such light reaches the low-loss, diffuser film of the present invention.
Therefore, “low-loss” means the absence of absorption of light in the diffuser film of the present invention when such light reaches such film from inside a lighted sign. A diffuser film of the present invention is low-loss even though it may be partially transmissive and partially reflective. For every 100 lumens reaching the diffuser film, 58 lumens might be reflected and returned to the lighted sign cavity and 41 lumens might be transmitted through the translucent surface. But only 1 lumen could be considered as absorbed by the diffuser film and lost to luminance efficiency. That means luminance efficiency using diffuser films of the present invention results in 99 luminance efficiency. With this unexpected luminance efficiency, the entire engineering science of lighted signs can be rewritten to take such superior luminance efficiency into consideration for energy consumption, lighting effect, or both.
Any significant absorption in the translucent surface of a lighted sign might occur within any co-laminates with the film to the translucent surface, namely, optional adhesive and substrate layers that could be needed to adhere and support, respectively, the diffuser film of the present invention to the translucent surface of a lighted sign.
Moreover, any significant absorption affects only the light transmitted by the diffuser film. Reflection of light from the interior side of the film back into the lighted sign cavity occurs without significant absorption.
When the reflectivity, R, of the diffusing film is greater than about 50 percent, light emitted by the source within the lighted sign cavity is, on average, reflected by the face and the walls several times before exiting the translucent surface of the lighted sign. This recycling of light within the lighted sign cavity is critical when uniform illumination of the transmitted light over the surface of the translucent face is required. The diffuser films of the present invention minimize loss of luminance efficiency and substantially and unexpectedly increase the efficiency of the recycling process of light reflected within the lighted sign cavity.
Optionally, but preferably, the low-loss diffuser film of the present invention is used in conjunction with diffuse reflective films that line the walls of the lighted sign cavity, as disclosed in copending, coassigned, U.S. patent application. Ser. No. 09/070,380, now abandoned, coassigned, U.S. Pat. No. 6,080,467, diffusely reflecting multilayer polarizers and mirrors (such as those disclosed in coassigned, U.S. Pat. No. 5,825,542, microporous membranes (such as thermally induced phase separated films as disclosed in coassigned, U.S. Pat. No. 5,976,686, the disclosures of which are incorporated by reference herein.
Briefly, such a film is applied to at least a portion of an interior surface of a lighted sign housing. It captures the lumens of light from the light source or those lumens of light reflecting back from a diffusing panel or sides and backs of the light cabinet or those lumens reflected by the translucent surface and re-emits such light with little loss until such light eventu
Deyak Frank L.
Freier David G.
Kaytor Scott R.
Strand Neal T.
3M Innovative Properties Company
Bjorkman Dale A.
Jones Deborah
Stein Stephen
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