Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02614873 2007-12-27
COLD-CATHODE FLUORESCENT LAMP ASSEMBLY FOR LIGHTING APPLICATIONS
This application is a division of copending, commonly owned, Canadian Patent
Application No.
2,479,631 filed August27, 2004.
FIELD OF THE INVENTION
The present invention relates generally to lighting sign applications and more
specifically to a
compact and cost-efficient assembly employing cold-cathode fluorescent lamps
in edge-lit emergency
lighting signs.
BACKGROUND OF THE INVENTION
The use of cold-cathode fluorescent lamps for general applications is well
known in the art. U.S.
Patent No. 6,135,620 provides one example showing the use of such lamps in
EXIT signs, traffic signals,
light bulbs and for general lighting applications.
Cold-cathode fluorescent lamps are desirable since they are more efficient and
offer savings in both
energy consumption and operating expenses. Such cold-cathode lamps operate at
a very low current
(although the voltage is quite high) and they have a longer life when compared
with standard fluorescent
lamps. Cold-cathode fluorescent lamps are low power consumption lamps with
long life expectancy and low
maintenance requirements. These lamps are often used to provide background
illumination in various lighting
applications. Cold-cathode fluorescent lamps require a substantial AC voltage
typically several hundred
volts, in order to achieve optimal light output. Although the frequency at
which a cold-cathode lamp is
driven varies, typically they are operated at a drive current frequency on the
order of about 10 50 KHz, and
have a life expectancy of 15,000 25,000 hours.
One difficulty with these types of lamps, as addressed by the above patent, is
in making it easy to
install and replace them. Generally cold-cathode fluorescent lamps are stand-
alone tubes having a variety
of plugs and wires extending therefrom for insertion into a dedicated socket.
Due to the fragility of the lamp
itself, extreme care must be taken during such installation as well as in
shipping, handling and storage.
Additionally, as indicated above, voltages required for cold-cathode
fluorescent lamp operation are generally
high (upwards of 1500 VAC) and thus inserting such a lamp when the fixture is
still powered creates the
potential for electrical shock.
Additionally, the lamp assembly using an edge-lit panel for emergency light
signs such as a lighted
exit sign is well known in the art. Typically, the panel includes a front side
and back side having two layers
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of paint, a colored layer for legend and a white layer for the background. The
light coming through
illuminates both the legend and the background while traveling through
multiple reflections and refractions
on panel surfaces.
Traditionally, a prior art edge-lit panel 50 of an exit or any other sign as
shown in Fig. 5 consists of
a glass or plastic (acrylic) panel having a front side 50a and backside 50b.
The panel 50 typically has two
layers of paint (screening), a layer 52 for the legend text (usually red or
green color) and a white layer 54 for
the background. The layers 52 and 54 are screened on the backside 50b of the
panel (the legend is in a
mirror). As an option the legend may have an engraved contour 59 which is
typical l" depth and width on
the backside of the acrylic panel 50 to accentuate the contrast between the
legend and background. The light
56 as shown by vertical lines falls from the top edge of the panel 50
illuminates both the legend 52 and
background 54 while traveling through multiple reflections 57 and refractions
58 on the surfaces of the panel
50.
This method has several disadvantages. First, poor uniformity of the
background illumination
(shadow around the legend letters), poor contrast ratio between the legend 52
and background 54, and a
certain colored light migration (pink shadow) from the legend 52 to the
surrounding background 54, due to
the multiple light reflections 57. In order to meet the UL924 visibility
requirements for exit signs, the
edge-lit panel 50 must be exposed to intense light sources (e.g.: two 8-Watt
fluorescent lamps) which
consume electrical power and dissipate heat.
In U.S. Patent No. 4,435,743, there is shown an edge-lit sign or panel that
has a translucent light
reflecting layer formed of white paint applied to the backside. Further, two
opaque layers are applied to the
front side of the device. In this method, the legend is not internally
illuminated, which makes the panel look
black and white, i.e., the legend remains black in complete darkness.
Therefore, this design would not meet
the requirements for a colored legend in both stand-by (AC) and emergency
mode.
The problems of the prior art are met with the invention of the parent
application, wherein a cold-
cathode fluorescent light assembly comprises: a lower housing unit and an
upper housing unit shaped to
cover the lower housing unit, wherein the lower housing unit is divided into
an upper frame and a lower
frame, the lower frame including a light reflector incorporated therein; first
and second cathode lamps
disposed within the lower frame, wherein the first and second cathode lamps
function independent of each
other; a first electrical circuit disposed within the upper frame and
connected to the first cathode lamp; and
a second electrical circuit disposed within the upper frame and connected to
the second cathode lamp,
wherein the first and second electrical circuits function independent of each
other.
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SUMMARY OF THE INVENTION
On the other hand the present invention may be considered as providing a
display light sign assembly
comprising: a parabolic-shaped reflector frame having top and bottom surfaces,
and side walls extending
from at least a first end to a second end.; an upper frame disposed on the top
surface of the reflector frame;
at least one cold-cathode fluorescent lamp disposed within the reflector frame
wherein the reflector frame
reorients radial beams from the lamp into parallel light beams; and at least
one essentially semi-transparent
elongated, protective panel attached to the reflector frame extending from the
first end to the second end,
wherein the parallel light beams are directed into the panel.
In another embodiment of the present invention, there is provided an edge-lit
panel comprising: a
front side and a backside, the backside including a semi-transparent frosted
surface; a white opaque
lamination glued onto the frosted surface; and a legend printed on the front
side using first and second layers
of semi-transparent materials. The first layer is white and the second layer
is colored. As light passes through
the first layer it splits in a manner that part of the light is reflected back
into the panel and the other part of
the light illuminates the second layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded perspective view of the component parts of the
invention.
Figure 2 is a top perspective view of the assembled unit of Fig. 1.
Figures 3A and 3B are exploded perspective views of the upper and lower
housing units,
respectively, of the assembly.
Figures 3C and 3D are section views of the upper and lower housing units,
respectively, of the
assembly.
Figure 4 is a transversal section view of the lower housing with a cold
cathode lamp and with an
edge-lit panel.
Figure 5 is a perspective view of a prior art edge-lit emergency exit sign.
Figure 6 is a perspective view of an edge-lit emergency sign of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to Figures 13 of the present invention, there is shown a
cold-cathode fluorescent
lamp assembly 10, mainly utilized for emergency lighting. Figure 1 shows a
perspective view of the
component parts of the lamp assembly while Figure 2 shows a top perspective
view of the assembled unit.
The assembly 10 is divided into an upper housing unit IOa and a lower housing
unit 10b. An exploded
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perspective view of the upper housing unit l0a and the lower housing unit l Ob
is shown in Figure 3A and
Figure 3B respectively. Additionally, a sectional view of the upper housing
unit l0a and the lower housing
unit lOb is shown in Figure 3C and Figure 3D, respectively.
The lower housing unit l Ob is made of two frames: an upper frame 12 and a
lower frame 13. The
upper frame 12 is a generally rectangular planar support frame, preferably
made of metal. The upper frame
12 includes a top planar surface 12a, a bottom planar surface 12b and
sidewalls 12c and 12d on two long
sides of the rectangular frame 12. The lower frame 13 is also a generally
rectangular support frame made
of metal. The lower frame 13 includes a top planar surface 13a, a bottom
planar surface 13b and side walls
13c and 13d on two long sides of the rectangular frame. The lower frame 13 is
connected to the upper frame
12. Specifically, the top surface 13a of the lower frame 13 is attached
longitudinally along to the bottom
surface 12b of the upper frame 12. The lower frame 13 is also known as a
reflector frame because the bottom
surface 13b is coated with a specular (shiny) metal deposition. Additionally,
two independent cold-cathode
fluorescent lamps 14a and 14b are disposed longitudinally in the reflector
frame 13 as shown in Figure 1.
The reflector frame 13 of the present invention serves two purposes. First, it
orients the light beam
and second, it protects the lamp against any mechanical stress. The reflector
frame 13 has a parabolic shape
for maximum focus towards an edge-lit panel. The reflector 13 preferably has
guiding edges and stoppers
to guide the edge-lit panel in the lamp proximity while protecting the lamp
against the impact with the panel
as will be described in detail below with reference to Figure 4.
Additionally, the upper and lower housings 10a, 10b serve as a packaging for
first inverter circuit
16a and a second inverter circuit 16b which are disposed on the top surface
12a of the frame 12. A portion
of the side wall 12d is open to accommodate the inverters 16 within the top
surface 12a. The top surface 12a
of the frame 12 includes a hole at each end through which wires extend to
connect the first inverter circuit
16a to lamp 14a and similarly connect the second inverter circuit 16b to lamp
14b. So, the upper frame 12,
serves mainly to package the inverters 16 and the reflector frame 13 serves
mainly to protect the lamps 14
and guide the light beams. The inverter circuits 16a and 16b are configured to
convert the received
low-voltage DC battery voltage from an outside power into a high AC voltage
appropriate to supply the
lamps 14a and 14b respectively as will be discussed below.
Additionally, this assembly 10 represents a redundant light source, i.e., if
one of the lamps 14a and
14b or inverter circuit 16a and 16b fails, the other one will continue to
light. Each of the lamps, 14a and 14b
with their own inverter circuits, 16a and 16b function independent of each
other. Further, it is understood
that while the lamp assembly 10 is shown having two lamps 14a and 14b, it may
have any number of lamps.
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The upper housing unit l0a is generally a rectangular planar cover preferably
made of metal, is
shaped to mate with the frame 12. The cover 10a includes a hole through which
preferably a power
connector such as a plug 20 is inserted with wires to connect the plug 20 to
the inverter circuits 16a and 16b.
The plug 20 provides DC line power to the circuits 16a and 16b. Sidewalls of
the cover 10a are shaped to
fit into slots (not shown) in frame 12. The cover 10a forms a mechanical
coupling surface shaped to engage
a groove in a housing (not shown in Figures I and 2) to facilitate insertion
and mounting of the assembly 10
to an emergency light sign such as an EXIT sign. Although the lamp assembly 10
is preferably to be made
of metal, other materials can be used such as plastic, PVC, etc.
In a preferred embodiment of the present invention, the inverter circuits 16a
and 16b in the lamp
assembly are provided with a low voltage and power consumption. The plug 20
provides this low voltage
DC line power to the inverter circuit 16a and 16b. The voltage power
preferably is in the range of 6Vdc to
12Vdc, thereby reducing and/or eliminating the risk of high-voltage hazard.
The inverter circuits 16a and
16b preferably include a high frequency switch mode power supply to convert
low DC line voltage into a
high AC voltage appropriate for lamps 14a and 14b, respectively. The inverter
circuits 16a and 16b are made
to be extremely compact and 16a and 16b are preferably coupled to a battery
charger and/or low-voltage DC
back up circuits (not shown) such as, 6V to 12V DC power supply. Therefore,
the circuitry in the lamp
assembly 10 requires only low voltage to be powered up. Also, all the voltage
components such as inverter
circuits 16a and 16b, wires etc. are inside the metallic lamp assembly 10,
which is electrically grounded to
the low-voltage socket. The combination of a lamp assembly powered from a low
voltage source and the
grounding of the metal housing, protects the user from electrical shock upon
installation or relamping even
with the exit sign powered by the AC line. Additionally, each inverter 16a and
16b has a built-in fuse to
disconnect a faulty or short circuit thereby preventing energy losses at the
power supply.
In another preferred embodiment of the present invention, the shape of the
reflector frame 13 is
parabolic, thereby allowing for a high-efficiency, sharp orientation of the
lamp radial beams into a parallel
light beams perpendicular to the panel edge. This is clearly displayed in
Figure 4 which shows a combination
of the lower housing unit I Ob of the lamp assembly 10 with a panel
installation 40. The lower housing unit
l Ob includes the upper frame 12 disposed on the top surface 13a of the
reflector frame 13 as shown in Figure
4. The cold-cathode lamp 14 is supported by the reflector frame 13 having a
reflector area 42. A panel 44,
preferably an edge-lit panel is essentially rectangular in shape and is
preferably made of plastic or other clear
materials. The pane144 is aligned to the lamp assembly by the side walls 13c
and 13d of the reflector 13 as
shown. As can be seen, the parallel light beams from the reflector 13 and the
lamp 14 fall directly into the
panel 44 and mainly remains focused therein. The majority of the reflected
rays from the light enter the
CA 02614873 2007-12-27
surface of the display panel 44. This is due to the parabolic shape of the
reflector 13. The reflector 13 also
has built-in panel stoppers 48 to guide the panel 44 in the proximity of the
lamp 14 so the light beams stay
within the panel 44, thereby further improving photometric efficiency.
Additionally, the stoppers 48 protect
the lamp 14 against the impact or accidental stress with the panel 44 keeping
the lamp 14 intact within the
reflector frame 13. Therefore, the parabolic shape reflector frame supporting
the lamps provides increased
lighting efficiency; mechanical protection of the lamps and guidance for
alignment of an edge-lit panel to
the lamp assembly.
In the present invention the edge-lit panel shown in Figure 6 is a rectangular
shaped panel 60 formed
of acrylic plastic or other clear materials. The panel 60 includes a front
side 60a and a backside 60b with
a semitransparent frosted surface 61 on its backside 60b. A white, opaque
lamination 62 such as plastic,
paper is preferably glued on the frosted surface 61 to increase the reflective
performance on the panel
backside 60b. The legend 64 including the word "EXIT" is printed on the front
side 60a of the panel 60 by
using two consecutive layers 64a and 64b of semi-transparent materials
(screening ink, plastic lamination,
etc.). The first layer 64a is white and has the role to split the light. The
second layer 64b is colored with
either red, green, blue, etc. The light falls from the top edge of the panel
60 as shown by straight vertical
lines 66. Part of the light is reflected back into the panel 60 as shown by
lines of multiple reflections 67,
improving the light uniformity on the background, the other part passes
through as shown by lines of multiple
refractions 68, and lights the second layer 64b of the legend 64. So, the
second layer 64b which is colored
and is illuminated by refracted light 68 coming from the panel. With this
method, the legend 64 can be
internally illuminated, i.e., red looks red in the panel 60 during complete
darkness. A legend contour 69 may
optionally be engraved on the legend side of the panel 60 as shown in Figure
6.
The edge-lit panel of the present invention as described above has several
advantages. First, there
is improved uniformity of the background having a frosted backside, white
lamination on the back, and a
white legend layer on the front side. Second, due to reflections from the
colored layer being eliminated, there
is no longer a colored, shadow on the background, i.e., white looks white.
Third, the contrast ratio between
the legend, i.e., colored layers and the background, i.e., semi-transparent
white surface can be controlled by
the transparency level of each of the two layers 64a and 64b.
In the edge-lit panel as described above, disclosed with both white layer 64a
and colored layer 64b,
however, the legend can optionally be printed without the colored layer. Also,
an additional transparent layer
of protection such as an acrylic can preferably be disposed on the front side
60a over the legend 64.
Alternatively, a double-faced edge-lit panel (not shown) can be made by either
installing two single-faced
panels back-to-back or by bending a double-length acrylic panel in a U-shape
form.
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While the particular embodiments of the present invention has been shown and
described, it will be
obvious to those skilled in the art that changes and modifications may be made
without departing from the
teachings of the invention. The matter set forth in the foregoing description
and accompanying drawings is
offered by way of illustration only and not as a limitation. The actual scope
of the invention is intended to
be defined in the following claims when viewed in their proper perspective
based on the prior art.
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