LED lamp

A LED lamp for use in lighted sign assemblies has a base configured to engage an associated electrical socket, a light array extending from the base, the base has conductive elements on the outer surface thereof to effect a power connection to the socket and internal contacts coupled thereto. The light array consists of three elongated circuit boards extending from the end of the base and oriented with respect to each other to form an array of triangular cross section. Each of the circuit boards has a multiplicity of light emitting diodes mounted upon its outer surface and spaced along its length, and a conductor connected to the diodes. A power transfer circuit electrically connects the circuit board conductor to the contacts in the base to provide electrical power to the diodes, and a generally tubular housing of light transmitting material mounted upon and extending from the end of the base in spaced relationship to the array.

BACKGROUND OF THE INVENTION 
The present invention relates to lighted exit and emergency signs, and, 
more particularly, to LED lamps for such signs. 
Exit and emergency signs are widely employed in commercial and industrial 
buildings, as well as in multi-unit residential buildings to identify 
exits and provide other information to persons who may be within the 
structure. Some such signs are continuously illuminated; others are 
illuminated only in the event of emergencies such as the loss of power; 
and still others are illuminated by the building power supply normally and 
by battery power when building power is lost. Such signs are usually 
illuminated by one or more incandescent or compact fluorescent lamps, each 
of which will normally have a rating of 15-25 watts. The use of 
incandescent and fluorescent lamps results in a power requirement which is 
particularly significant when the signs are powered by a battery supply in 
the event of an emergency. 
There have been efforts to utilize light emitting diodes (LEDs) to effect 
illumination of exit and emergency signs so as to reduce the amount of the 
power required, and such efforts have necessarily involved the use of a 
relatively large number of spaced light emitting diodes to provide the 
necessary candlepower for adequate illumination. In some such signs, the 
light emitting diodes have been oriented in rows corresponding to the 
configuration of the letters in a stencil or lettered plate under which 
they are disposed. Because of this orientation, an undesirable result is 
that the light emitting diodes produce a multiplicity of bright spots in 
the illuminated legend of the sign even when diffuser material is placed 
between the LEDs and the legend stencil or plate. 
In addition to the lower power consumption (an array may require only 2 
watts), light emitting diodes generate less heat and accordingly are much 
longer lived. The lower power consumption also enables the reduction of 
the size and cost of DC power supplies to provide emergency power. 
Accordingly, there are decided advantages to employing LEDs despite the 
objectionable point source appearance. 
Recently, there have been efforts to utilize LED lamps as replacements in 
existing incandescent signs. These lamps have used one or two lamp bases 
which seat a circuit board with LEDs mounted thereon inside a glass 
tubular housing. With either the single or double board version, the lamps 
must be positioned in the socket so that the face of the board is 
substantially parallel to the stencil plate if maximum illumination of the 
stencil is to be obtained. Moreover, the light emitted is highly 
directional rather than diffuse. 
It is an object of the present invention to provide a novel LED lamp for 
exit and emergency signs incorporating light emitting diodes as the light 
source which is not critical to its orientation relative to the stencil 
and which provides relatively diffuse illumination of the indicia of the 
sign legend. 
It is also an object to provide such an LED lamp providing a substantially 
uniformly lighted appearance for the characters of the legend. 
Another object is to provide such an LED lamp which can readily replace the 
incandescent and fluorescent light units in existing exit and emergency 
signs having single and double face stencil plates. 
Yet another object is to provide such an LED lamp which can easily be 
manufactured with different types of lamp bases including candelabra 
screw, medium screw, intermediate screw, single or double contact bayonet, 
and the PL (bi-pin) base used with compact fluorescent lamps. 
A further object is to provide such an LED lamp which may be fabricated 
readily and economically from components which may be readily assembled. 
SUMMARY OF THE INVENTION 
It has now been found that the foregoing and related objects may be readily 
attained in a LED lamp having a base which is configured to engage an 
associated electrical socket. The base has conductive elements on the 
outer surface thereof to effect a power connection to the socket and 
internal contacts coupled thereto. 
Three elongated circuit boards extend from the other end of the base and 
are oriented with respect to each other to form an array of triangular 
cross section. Each of the circuit boards has a multiplicity of light 
emitting diodes mounted upon the outwardly disposed surface thereof and 
spaced along the length thereof. The circuit board also has conductor 
means connected to the diodes. 
Power transfer means is provided for electrically connecting the conductor 
means of the circuit boards to the contacts in the base and to provide 
electrical power to the diodes. Mounted upon and extending from the other 
end of the base in spaced relationship to the diodes is a generally 
tubular housing of light transmitting material. 
Desirably, there is included connector means for joining the circuit boards 
to hold them in the array, and this is effected by notches in the sides of 
the boards adjacent their ends, in which are seated connector means 
comprising circular wire clips. The power transfer means includes means 
for converting alternating current to direct current, and the means for 
converting alternating current includes an AC input capacitor and an AC to 
DC converter. Preferably, the AC input capacitor is a cylindrical film 
capacitor axially extending between the base and the adjacent end of the 
circuit boards. 
Desirably, the base has apertures therein to allow air to pass therethrough 
into and from the interior of the generally tubular housing, and the 
circuit boards are of substantially equal dimension and the cross section 
of the array is an equilateral triangle. 
An emergency sign utilizing the lamps includes a housing, at least one 
plate providing indicia thereon mounted in the housing, and at least one 
lamp socket in the housing behind the plate. The LED lamp is seated in the 
socket and illuminates the indicia plate. 
Usually, the sign has two indicia bearing plates disposed on opposite sides 
of the housing and the socket and lamp are disposed therebetween.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
Turning first to the embodiment of FIGS. 1 and 4-7, therein illustrated is 
an elongated LED lamp embodying the present invention which is comprised 
of a generally tubular glass housing 10, a generally triangular light 
array generally designated by the numeral 12, an AC film capacitor 16, and 
a base designated by the numeral 20. This lamp is intended for use in an 
incandescent lamp socket. 
The glass housing 10 is either clear or it may be frosted to diffuse the 
light. The end 11 of the housing 10 is semispherical and the other end 13 
provides a circular opening. The glass housing 10 provides mechanical 
rigidity to the lamp assembly and protects the light array 12 from direct 
contact. If frosted, it will also diffuse the light passing therethrough. 
The light array 12 comprises three elongated printed circuit boards 24 of 
equal length and width which are assembled in side-to-side relationship to 
provide a triangular cross section, equilateral triangular configuration. 
Each of the boards 24 includes a multiplicity of LEDs 26 in a rectilinear 
row, and the longitudinal axes of the rows of LEDs in the array are spaced 
apart 120.degree.. Although the glass tube 10 helps disperse the light 
generated by the LEDs 26, the relatively uniform dispersion of light is 
mainly due to the novel triangular configuration of the light array 12. 
The lamp base 20 includes a threaded, generally tubular metallic element 44 
with a contact 40 at its lower end and an enlarged cup shaped collar 
portion 42 at its upper end. Seated in the collar portion 42 is the 
cylindrical base 34 on the mounting member generally designated by the 
numeral 14 which has a larger diameter cup shaped body portion 32 with 
axially extending passages 36 therethrough. The upper surface of the body 
portion 32 is configured to seat the lower end of the cylindrical AC film 
capacitor 16. Adhesive (not shown) may be used to bond the metallic 
element 42 and mounting member 14, and may also be used to bond the AC 
film capacitor 16 and the metallic element 44. The glass tube 10 seats 
snugly within the cup shaped body portion 32 and is adhesively bonded 
thereto. 
As seen in FIGS. 4, 5 and 7, two wire clips 46 seat in special shaped 
notches 48 located adjacent the ends of the printed circuit boards 24 to 
assemble the boards 24 and provide mechanical rigidity. 
As seen in FIG. 1, the electrical circuit assembly includes an input AC 
film capacitor 16, which together with diodes 28 and a resistor 29, as 
seen in FIG. 5, convert the input AC (alternating current) to DC (direct 
current) as required by LEDs 26 without any step-down transformer as in 
common practice. In addition, interconnecting circuit board leads 30 are 
soldered to the conductive paths on adjacent circuit boards 24 to provide 
an electrical connection between the individual circuit boards 24 of the 
light array 12. 
The end of the light array assembly 12 nearest to the lamp base 20 abuts 
one end of the axial-lead AC film input capacitor 16. The capacitor 16 is 
a cylinder and a circular bushing 50 is seated within the triangular array 
12 to facilitate the alignment of the longitudinal axis of the capacitor 
16 and of the board array 12 as illustrated in FIG. 6. 
The AC film capacitor 16 is seated within the base 20 and projects through 
the aperture 38 in the mounting member 14. The capacitor lead 22 is 
soldered to the contact 40 on the base 20 where it will be supplied AC 
power through a corresponding contact in a mating electrical socket (not 
shown). To complete the circuit, the return wire 18 is soldered to the 
inside conductive wall of the base 20. 
A board lead 23 has one end soldered to the back of one of the circuit 
board strips 24 and another end soldered to the capacitor 16. The board 
lead 23 is passed through PVC tubing 52 (seen in FIG. 3) to provide 
isolation between it and the conductive circuit on the back of printed 
circuit boards 24. 
The passages 36 allow air to circulate between the exterior and interior of 
the tube 10. 
A candelabra screw type base 20 is illustrated in FIGS. 1 and 7. However, 
the base 20 can have different configurations and contacts including a 
concentrical, intermediate or medium screw, a bayonet single (not shown), 
or a double contact (bi-pin) base seen in FIGS. 2-3 designed to fit 
compact fluorescent lamp sockets. 
In the embodiment of FIGS. 2-3, the base 20a has a cover 54 which provides 
an interface between the mounting member 14 and PL (bi-pin) base 20a. Both 
the capacitor lead 22 and the return wire 18 pass through the aperture 56 
in the cover 54 and each is soldered to a separate pin 58 of the PL 
(bi-pin) base 20a. The base 34 of the mounting member 14 extends through 
the aperture 56 and seats in the base 20a. A thin layer of adhesive 
between the surface of the mounting member 14 and cover 54 and between the 
base 34 and the interior of the base 20a bonds these elements. 
The advantages of an LED lamp include longer life and less power 
consumption than comparable incandescent and fluorescent lamps. In 
addition, unlike compact fluorescent lamps, the LEDs do not require 
special ballasts to match them to the recommended voltage and current 
rating. Thus, the LED lamp with PL (bi-pin) base adaptor 20a is a direct 
replacement for existing compact fluorescent lamps without any concern for 
the ballast rating and/or any need for wiring modifications. 
The alternative PL (bi-pin) embodiment of the LED lamp is adapted to be 
inserted into the housing of existing lighted sign assemblies as a direct 
replacement light unit for the fluorescent lamps of the original 
equipment. The major advantage is that the LED lamp is able to replace the 
existing compact adaptor without any need to remove the installed ballasts 
and/or any modifications done to the internal wiring of the already 
installed signs. 
Turning next to FIG. 8, therein fragmentarily illustrated is an exit sign 
utilizing the LED lamps embodying the present invention and generally 
designated by the numeral 60. The exit sign includes two lettered stencils 
68 and glass faceplates 70 mounted on either side of the exit sign housing 
62. Two LED lamps 60 are spaced within the housing 62 and seated within 
electrical sockets 64, which are in turn connected by wiring 66 to an 
outside power source to energize the light array 12. 
Turning next to FIG. 9, therein schematically illustrated is the circuitry 
of the LED lamp of FIG. 1. The voltage of the AC power source 72 is 
reduced by the film capacitor 16, and then rectified by the diodes 28 into 
DC current. This DC current is then limited by the resistor 29 which is 
connected in series to each circuit board 24 to power the LEDs 26. 
Due to the highly directional nature of LEDs, a single board LED lamp 
cannot evenly illuminate a two faced exit sign 62. As a result, a single 
board LED lamp cannot be used effectively in a double faced exit sign. 
Although a double board LED lamp is more effective than a single board LED 
lamp in a double faced exit sign, the LED boards must still be carefully 
oriented parallel to the faces of the exit sign in order to effectively 
illuminate the two faces of the exit sign. This will likely cause an 
installer to either mount the double board LED either too loosely in the 
socket thereby degrading the electrical connection or too tightly in the 
socket thereby over torquing the lamp. In contrast to the single or double 
board LED lamps, the novel triangular array of the circuit boards 24 and 
their corresponding LEDs 26 create a non-directional light source, the 
orientation of light array 12 is inconsequential. 
Thus, it can be seen from the foregoing detailed description and the 
attached drawings that the LED lamps of the present invention provide 
relatively uniform illumination of the indicia of the sign legend plate 
and do not require any special rotated orientation relative to the plane 
of the plate since the light rays are emanating about the entire 
circumference of the lamp. Moreover, the LED lamp can easily be 
manufactured with different types of lamp bases, including candelabra 
screw, medium screw, intermediate screw, bayonet single or double contact 
base, and the PL (bi-pin) base used with compact fluorescent lamps.