Card – picture – or sign exhibiting – Illuminated sign – Lamp box
Reexamination Certificate
1999-05-12
2002-04-09
Green, Brian K. (Department: 3628)
Card, picture, or sign exhibiting
Illuminated sign
Lamp box
C362S377000, C362S223000, C313S025000
Reexamination Certificate
active
06367179
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an illumination source for illuminating a planar surface with a small number of tube-shaped lamps. More particularly, the present invention is directed towards an illumination source for emergency exit signs and emergency exit sign retrofit kits.
BACKGROUND OF THE INVENTION
An illuminated display sign generally comprises a light source to illuminate a display surface upon which words, symbols, or other indicia are imprinted. Illuminated display signs include a variety of advertising signs, household number display signs, information bearing signs, and a variety of emergency information signs.
As shown in
FIG. 1
, a common illuminated display sign is an emergency exit sign. Although there are a variety of exit sign configurations, a common prior art emergency exit sign
10
utilizes a rectangular shaped frame, and is commonly known as a “box type” emergency exit sign. Two surfaces
12
,
24
of the exit sign
10
are used to display information. Stencil signs have translucent letters and opaque backgrounds. Panel signs have white translucent backgrounds and translucent letters. The display surfaces
12
,
24
of emergency exit sign
10
include directional arrows
16
and letters
18
forming the word “exit.”
A variety of local regulations, safety organizations, and customs govern the exact size and placement of directional arrows
16
and letters
18
so that there are currently several different size and styles of box-type exit signs installed throughout the United States. The rectangular frame size varies across the United States, but typically is between 8″-to-14″ wide, 7″-to-11″ high, and 1.75″-to-4″ deep. The exit sign letters are typically between 6.0″-to-8″ tall and ¾″ wide. The directional arrows
16
are typically disposed to the sides of the letters
18
, but are also sometimes placed below the letters.
A suitable light source is required to illuminate the arrows
16
and letters
18
of an emergency exit sign
10
.
FIG. 2
shows a perspective view of the interior of a prior art exit sign with one exterior surface
12
removed for the purpose of illustrating the interior illumination means. Exit signs
210
of the type show are commonly manufactured with two sockets
220
to hold two incandescent bulbs
230
. The sockets are typically spaced apart along an upper edge
240
of the sign
210
. The incandescent bulbs
230
typically comprise two twenty-watt incandescent lamps.
The cost of operating a single emergency exit sign
210
utilizing incandescent-bulbs
230
can be significant. In addition to the cost of the electricity, the bulbs must be replaced biannually because of the limited operating lifetime of common incandescent bulbs. The average annual operating cost of one emergency exit sign typically averages about $50 per year.
The development of high efficiency light-emitting diodes (LEDs) permits LEDs to be used instead of incandescent bulbs. A single LED has a light output that is highly directional and confined to a narrow cone of emission angles, which makes it difficult to use a small number of LEDs to brightly illuminate an emergency exit sign. Consequently, the light output from a large number of individual LEDs, each disposed at different locations and/or pointed in different directions, is typically needed to brightly illuminate an emergency exit sign. Exit signs utilizing an illumination source comprised of LEDs use about 90% less power than incandescent bulbs and have an output illuminance above the minimum brightness requirement required by Underwriter's Laboratory® requirements which can be maintained for a useful lifetime of about 3-10 years. The power output of LEDs depends upon the color (wavelength) of the LED emission. Generally, the most efficient LEDs have a light with a red (long wavelength) color light output, although substantially dimmer LEDs with a green (short wavelength) output are commercially available as well. However, green LEDs with an output power comparable to red LEDs are now commercially available. Because of the monochromatic (single color) output of LEDs, they are best suited for illuminating stencil signs. Currently, about 80% of manufactured red stencil signs are illuminated by LEDs. This is in contrast to the early 1990s, when about 80% of exit signs were illuminated with incandescent lamps.
The standards for brightness and uniformity of illumination of the arrows
16
and letters
18
of an exit sign
10
have become more stringent in recent years in order to address concerns about public safety. A brighter, more uniformly illuminated emergency exit sign is easier to read under a variety of background illumination conditions and/or from a greater distance.
There are currently two separate sets of Underwriter's Laboratory® (UL) standards for emergency exit signs under the UL 924 standard which was issued August, 1997. The first set of standards is for new exit signs. New exit signs must have a minimum brightness of 2.5 foot lamberts (FL) as measured along each of twenty different points. The twenty measurement points of the UL 924 standard along different portions of the letters
18
of an emergency exit sign is shown in FIG.
3
. There is also a minimum uniformity ratio (UR) requirement in regards to the maximum/minimum intensity of any two of the twenty points. New exit signs must have a maximum UR of 50:1 over the letters
18
and arrows
16
, which means that the dimmest of the twenty measured points can have an optical intensity that is at most fifty times lower than the brightest of the twenty points.
A variety of conventional illumination sources may be used to satisfy the UL 924 standard for new exit signs. For example, conventional LED illumination sources used in emergency exit signs typically direct the light output of a large number of individual LEDs to illuminate the letters
18
of an exit sign. Conventional LED illumination source configurations produce an output of about 3 to 8 FL, which diminishes with age to 2.5 FL in a time period of six months-to-ten years.
The second set of UL 924 standards is for retrofit kits, with these standards being more stringent than for new exit signs. Retrofit kits include any kit to replace the standard light source of a conventional exit sign with another light source, such as an energy efficient LED light source. A retrofit kit must be capable of illuminating the letters of a retrofitted exit sign with a minimum brightness at each measurement point in excess of 6 FL and a UR of 20:1. These standards are so stringent that they exceed brightness levels achieved in conventional LED illumination sources (i.e., using common numbers and configurations of LEDs) used in new emergency exit signs.
The problem of designing a retrofit kit to satisfy the UL 924 retrofit standard is exacerbated by the many different sizes and styles of a box-exit sign currently in existence. Under the old retrofit standards, a LED illumination source with a modest number of LEDs could satisfy the illumination requirements of a variety of box-type emergency exit stencil signs. However, under the new retrofit standards, a comparatively large number of LEDs are required to form an illumination source that is bright enough and uniform enough to satisfy the present retrofit standards. Consequently, the cost of an LED retrofit kit is prohibitive when compared to the fewer LEDs needed in a new sign. Several manufacturers have ceased selling LED retrofit kits in favor of selling new exit signs. Unfortunately, the lack of LED retrofit kits may delay the conversion of the estimated 100-to-150 million emergency exit signs in the United States to more energy efficient illumination means. Even if LED illumination sources were suitable for retrofitting stencil-type signs, they are unsuitable for retrofitting panel signs because conventional LEDs have a substantially monochromatic light output. Panel signs require a white-light source to illuminate their translucent letters and
BJI Energy Solutions LLC
Green Brian K.
Kleinberg Marvin H.
Kleinberg & Lerner ,LLP
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