A tubular LED light source.
The .present invention relates to a tubular LED light source, comprising a bulb portion having an outer tubular wall of translucent material, a plurality of light emitting diodes (LED) disposed inside said bulb portion with a substantially uniform distribution over the length thereof and over the inside circumference of said outer wall and electrical power supply connectors (3) for said light emitting diodes (LED) .
As such the use of light emitting diodes (LED's) for a multitude of different lightening purposes have become well-known in the art, typical ex- amples being so-called strip-lights as ■ used for emer-^ gency purposes and directional . guidance in aircrafts, theatres etc. and various forms of light sources for information, entertainment and/or advertising purposes. Typical examples can be found in the following prior art publications: US-A1-2001-16105, US-A1-2001- 36082, US-A1-2002-114168, US-A-6 , 145 , 996 , WO 96/19093, WO 99/06759, WO 00/31463 and WO 02/31463.
With the development of light emitting diodes (LED's) to provide increased light output the use of - LED-based light sources have become an option as substitution for fluorescent light tubes for many of the lightening purposes, for which the use of fluorescent light tubes has conventionally been preferred for economic reasons in terms of energy consumption and operational life. Compared to ordinary fluorescent light tubes LED-based light sources will typically provide improvement in respect of reduction of energy consumption, reduced heat emission, significant ex-
tension of operational life and elimination of flashing of the light source on ignition and environmental hazards resulting from the content of gases in fluorescent light tubes. In US-A1-2002 0060526 a tubular LED light source is disclosed, which has the same dimensions and end caps as a conventional fluorescent light tube and is suitable for mounting in a conventional fluorescent light tube socket. One or more groups or ar- rays of LED's are mounted on one or more surfaces of a common circuit board extending in a plane parallel to the axis of the tubular bulb portion of the light source to emit light through one or more sides of the bulb portion. To provide structural strength to the circuit board along the length of the bulb portion the circuit board is designed with a H-shaped cross- sectional profile, and each of the LED's is mounted on the circuit board at an angle with respect to adjacent LED's to produce a predetermined radiation pattern or dispersion of light, whereby the geometrical structure and the mounting of the light source become complicated.
In another prior art example of a tubular LED light source, disclosed in DE-U1-200 13 605 a number of linear LED arrays are disposed on individual side faces of a tubular member arranged inside and coaxial with the tubular bulb portion of the light source and having the cross-sectional profile of a regular polygon, such as a regular octagon, such that each LED array forms a linear chain directed in the axial direction of the tubular light source. Although the geometrical configuration of this light source provides an improved light distribution, the need for an
additional tubular inner member for mounting of the LED's adds to complication and costs of the device.
On the background of this prior art it is the object of the invention to provide a tubular LED light source of the kind set forth of a significantly simpler geometrical configuration, which is useful as a substitution for conventional fluorescent light tubes in any application thereof ranging from ordinary lightening applications to specific applications like various forms of coloured and XJV light sources.
According to the invention this object is achieved by a tubular LED light source as defined, which is characterized in that the light emitting diodes (LED) are confined to a plurality of individual LED configurations disposed in distinct radial planes in the bulb portion and each comprising a number of light emitting diodes arranged with substantially uniform spacing and at substantially equal separation from said inside circumference of the outer wall of the bulb portion, said configurations forming individual electrical LED arrays in connection with said power connectors .
The disposition of individual groups or arrays of LED's in a plurality of distinct radial planes provides a simple geometrical structure to the light source together with a low consumption of materials and a simplified manufacture and mounting of the light source.
Advantageous and preferred embodiments of the light source according to the invention are set forth in the dependent claims .
In one preferred embodiment the number of light emitting diodes of each of said configurations is ar-
ranged at the circumference of a common supporting disk member such as a printed circuit board member disposed in one of said radial planes.
The disk member of each configuration may have the form of a substantially regular polygon with a number of sides equal to the number of light emitting diodes in said configuration, the light emitting diodes being mounted at individual sides of the board member. The disk members of all configurations of light emitting diodes may advantageously be interconnected by a single substantially flat and rigid connection member such as a printed circuit board member extending substantially in an axial plane of the light source and providing electrical conductors for the LED arrays, provided by the configurations.
In a further development of this embodiment a desired substantially uniform light distribution over the length and circumference of the bulb portion may be obtained by connection of the disk members (5) of the LED configurations with the single connection member with the discrete positions of the light emitting diodes alternating between said radial planes.
Preferably, the LED configurations may comprise equal numbers of light emitting diodes ranging from 3 to 15 light emitting diodes and may be disposed with a substantially uniform separation of 15 to 100 mm
Other features and advantages of the invention will become apparent from the accompanying schematic drawings, in which
Fig. 1 is a perspective view of a straight linear embodiment of a tubular LED light source according to the invention;
Fig. 2 is a cross-sectional view of the embodiment in fig. 1 showing a single LED configuration therein;
Fig. 3 shows an alternative embodiment of a single LED configuration for a tubular LED light source according to the invention;
Figs. 4 and 5 show alternative configurations of tubular LED light sources according to the invention; and Fig. 6 is an example of an electrical diagram for a light source as shown in fig. 1.
In the embodiment shown in fig. 1 the tubular LED light source according to the invention comprises a substantially straight linear tubular bulb portion having an outer wall 1 of a translucent material, which may typically be clear or frosted glass, plastics such as acrylic materials or the like. The tubular outer wall 1 is connected with end caps 2, in which power connectors 3 are disposed, e.g. by being embedded in electrically insulating material. The power connections 3 may comprise pin connectors of a form allowing mounting of the LED light source in a standard socket for fluorescent light tubes.
Inside the bulb portion a number of configura- tions 4 of light emitting diodes are disposed in distinct radial planes distributed along the length of the tubular bulb portion with a substantially uniform separation. Typically, the separation of adjacent radial planes for the LED configurations 4 may be in the range from 20 to 50 mms .
As shown in fig. 2, each of the configurations 4 may comprise a common support member, which in the illustrated embodiment is formed by a disk-shaped
printed circuit board member 5 having a circumference fitting the inside of the tubular outer wall 1. The printed circuit board member 5 may have a circumference in the shape of a substantially regular polygon such as an octagon. Light emitting diodes (LED's) 6 are mounted at the circumferential edge of the disk 5 with a substantially uniform spacing, preferably with one LED at each side of the polygonal circumference, and at a short substantially equal separation from the inside of the outer wall 1. The LED's 6 may be electrically connected in series to form an individual LED array by means of electrical conductors 7 printed on the printed circuit disk 5.
As shown in fig. 1, the printed circuit disks 5 of the LED configurations 4 may be mechanically and electrically interconnected by a common elongate and substantially flat and rigid connection member such as a printed circuit board 8 extending in an axial plane throughout the length of the bulb portion be- tween the end caps 2. For engagement with the circuit board 8 each of the printed circuit disks 5 may be formed with a narrow slit 9 matching the thickness of the printed circuit board 8 and extending from the center of one of the sides of the polygonal circum- ference of the disk 5 to a slit bottom spaced from the opposed side of the polygonal circumference of the disk. Correspondingly, a number of shorter slits 10 may be formed as seen in fig. 1 with uniform spacing along one of the longitudinal side edges of the circuit board 8 for accurate localisation of the disks 6 in substantially uniformly spaced radial planes.
By this arrangement a tubular LED light source
is obtained with a substantially uniform light emission along the length and circumference of the bulb •.portion.
As illustrated by dashed lines in fig. 2 the slits 9' may alternatively be formed to extend from a corner of the polygonal circumference of the disk 5 and disks provided with such slits may alternate with disks radiating inwards from the center of a polygon side, whereby the light distribution in the circum- ferential direction may be further improved.
In the alternative embodiment of a single LED configuration shown in fig. 3 the common support member for the LED's 6' is formed by an annular moulded member 11 of translucent material such as a transpar- ent acrylic material, in which the LED's 6' are encapsulated together with electrical conductors 7' . At the inner circumference of the annular acrylic member 11 engagement projections 12 may be formed for engagement with the common connection member 8'. As alternatives to the straight linear tubular LED light source shown in fig. 1 other possible shapes of tubular LED light sources according to the invention are shown in figs. 4 and 5. Fig 4 illustrated a light source 13 forming a closed ring, in which Individual LED configurations 4'. are disposed in radial planes with a separation substantially as shown in fig. 1. Fig 5 shows a light source 14 bent into an U-shaped configuration, equally with individual LED configurations 4'' disposed in distinct ra- dial planes. For non-linear or curved configurations as illustrated in fig. 4 and 5 the common connection member (not illustrated) for the LED configurations 4' and 4'', respectively, may be formed of a flexible
material, which can be deformed to follow the nonlinear or curved shape of the bulb portion.
According to the simplified example of a wiring, diagram shown in fig. 6 AC mains voltage is supplied to a power supply arrangement 15 provided on the printed circuit board 8, from which DC operation voltage is applied in parallel to all the LED configurations 4, within each of which operation current is supplied to the series-connected LED's 6 via a re- sistor 16 acting as a current limiter.
Whereas the invention has been described with reference to a few exemplified embodiments, it will be apparent to persons skilled in the art that many modifications in detail will be possible to accom- plish the structure according . to the invention with LED's disposed in a number . of distinct radial planes of a tubular bulb portion with substantially uniform spacing over the length and circumference thereof.