Lighting Device

Abstract

The lighting device 10 comprises an elongated arrangement of LEDs 14 having outer rows r1, r2 of LEDs extending along a length direction and at least one inner row r3 of LEDs between the outer rows r1, r2 of LEDs. The pitch p1 of the LEDs in the inner row r3 is greater than the pitch p2 of the LEDs along the first and second outer rows r1, r2. Thus, by having a smaller pitch, unevenness in the outer rows r1, r2 is reduced.

Description

[Technical field]

[0001] The present invention relates to a lighting device, in particular to a lighting device comprising an elongated carrier on which LEDs are mounted. [Background technology]

[0002] There are different types of elongated LED lighting devices, including linear luminaires and tubular LED lamps. In all cases, the LEDs are discrete units, e.g., surface mounted LED chips mounted in a regular array on a substrate such as a PCB.

[0003] A tubular LED lamp is provided with pin terminals at each end for receiving in, for example, a so-called G13 lampholder. The lamp comprises a plastic or glass tube, in particular a so-called T8 tube, an aluminium heat sink which holds the LED substrate, and a driver.

[0004] To achieve a desired range of emission angles, a desired light efficiency and lumen output, the LED substrate is typically mounted face-down into the top of an optical cavity defined by the tube.

[0005] A plastic tube is used with, for example, a plastic lamp holder, fixed with screws or glue, and the LED PCB board is mounted on an aluminum heat sink. This lamp has good mechanical properties, reliability and safety.

[0006] The glass tube is fixed to the lamp end cap, for example, using an epoxy adhesive. The LED substrate, which may comprise a PCB or a flexible circuit board, is typically glued to the inside of the glass tube using silica gel. Summary of the Invention [Problem to be solved by the invention]

[0007] One problem with this common type of lighting device is that the individual LED chips can be visible, resulting in what is known as "unevenness" that can be seen by the eye. This occurs when the LED chips are far enough apart and there is insufficient mixing of the light output from adjacent LED chips, resulting in individual LEDs being visible from outside the lamp. [Means for solving the problem]

[0008] One way to reduce the unevenness is to reduce the pitch between the LEDs, however this increases the number of LEDs required and is less cost effective for a given desired overall lumen output.

[0009] The invention is defined by the claims.

[0010] According to an example according to one aspect of the present invention, A long career and an LED arrangement along the length of an elongated carrier, A lighting device is provided in which the LED configuration comprises at least first and second outer rows of LEDs extending along a length direction and at least one inner row of LEDs between the first and second outer rows of LEDs, the pitch of the LEDs along the at least one inner row being greater than the pitch of the LEDs along the first and second outer rows.

[0011] The lighting device has multiple rows of LEDs to generate the desired light output luminous flux. However, instead of arranging the LEDs in a regular grid, one or more inner rows have a larger pitch than the outer rows. The outer rows are the rows that are laterally closer to the sides of the carrier and therefore closer to the outside world (when viewing the lighting device from either side). As a result, the unevenness of these LED rows (i.e., the visibility of the individual LED chips) is more apparent from the outside of the lighting fixture. By arranging these rows with a smaller pitch (i.e., with the LEDs closer together), the unevenness is reduced for lateral viewing angles. In this way, the overall configuration of the LEDs results in a more uniform light appearance. By arranging the LEDs in this way, with rows of different LED pitches for a given number of LEDs, the overall unevenness of the lighting device is reduced compared to a regular LED array, especially for tubular LED lamps (TLEDs) with high transmittance tubes. On the other hand, the central intensity is reduced (compared to the outer rows) and therefore the overall uniformity of the TLEDs is improved.

[0012] There may be three rows of LEDs (one middle row and two outer rows), but there may also be more than three rows with a gradually increasing pitch towards the middle.

[0013] At least one inner row of LEDs may be aligned, for example, along a centerline of the carrier. The light output distribution may be symmetric, for example, in a plane perpendicular to the length of the elongated carrier.

[0014] The lighting device may further comprise a light-transmitting housing around the carrier, which may be substantially transparent, or more preferably may be translucent and have diffusing or scattering capabilities, which reduces visible unevenness.

[0015] The light-transmitting housing may, for example, comprise a tube having a circular cross-sectional shape. The tube may be made of plastic or glass.

[0016] The carrier is preferably mounted against the inner surface of the tube, away from the central axis of the tube. This maximizes the light transmission distance from the carrier to the tube, and therefore maximizes light mixing before the LED output light reaches the tube.

[0017] For example, the tube has a wall thickness adjacent a side of the carrier that is greater than the wall thickness on the opposite side facing the LEDs on the carrier.

[0018] This greater wall thickness is provided in the locations of the outer rows of LEDs closer to the wall, which results in greater scattering by the tube material, thereby further reducing the uniformity of those outer rows of LEDs.

[0019] The carrier may for example comprise a printed circuit board, and the lighting device may further comprise a heat sink to which the printed circuit board is attached.

[0020] The heat sink is, for example, aluminum.

[0021] The lighting device may comprise a tubular LED or a linear luminaire.

[0022] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0023] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Figure 1] 1 shows a lighting device in the form of a tubular LED lamp. [Diagram 2] 2 shows a cross section perpendicular to the length of the lighting device of FIG. 1; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described with reference to the figures.

[0025] It should be understood that the detailed description and specific examples, while illustrating exemplary embodiments of the devices, systems, and methods, are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to denote the same or similar parts.

[0026] The present invention provides a lighting device with an elongated LED configuration having outer rows of LEDs extending along a length direction and at least one inner row of LEDs between the outer rows of LEDs. The pitch of the LEDs in the inner rows is greater than the pitch of the LEDs in the first and second outer rows. Thus, by having a smaller pitch, unevenness in the outer rows is reduced.

[0027] FIG. 1 illustrates in simplified schematic form a lighting device 10 in the form of a tubular LED ("TLED") lamp. In the top image, FIG. 1 shows a perspective view showing hidden internal details, and in the bottom image, a close-up of a portion of the top image. TLED lamps can be used as a direct replacement for traditional fluorescent tubes. In this way, the benefits of solid state lighting are obtained without incurring the expense of modifying existing light fixtures.

[0028] The lighting device comprises an elongated carrier 12, such as a rigid or flexible PCB, having an arrangement of LEDs 14 along the length of the elongated carrier 12.

[0029] The elongated carrier 12 is mounted on a heat sink 16, such as an aluminum heat sink, within an outer tubular housing 18. For tubular LEDs, the outer tubular housing 18 is typically a cylindrical plastic or glass tube. However, the tube may be non-circular, and thus tubular LEDs are not limited to the circular profile of traditional fluorescent tubes.

[0030] The carrier 12 is mounted against the inside surface of the tube, away from the central axis of the tube. This maximizes the light transmission distance from the carrier to the tube, and therefore maximizes light mixing before the LED output light reaches the tube.

[0031] End caps 20 are secured to the ends of the tubes and include electrical connection pins 22. Each end cap has two pins 22 parallel to the elongated axis of the tubular housing 18, offset on each side from the central axis of the end cap 20. Each end cap electrically connects to an internal driver board (not shown) and to the PCB that mounts the LEDs.

[0032] In accordance with the present invention, the LED 14 configuration comprises first and second outer rows r1, r2 of LEDs 14 extending along a length thereof, the outer rows extending along a side of the carrier 12. Between the first and second outer rows r1, r2 is an inner row r3 of LEDs.

[0033] The pitch p1 of the LEDs along the inner row r3 is greater than the pitch p2 of the LEDs along the first and second outer rows r1, r2.

[0034] The total number of LEDs (i.e., in all rows combined) is selected to produce a desired light output flux, however, instead of arranging the LEDs in a regular grid, the inner rows have a larger pitch p1 than the outer rows.

[0035] The outer rows are closer to the inner wall of the tubular housing 18 than the inner rows. As a result, the unevenness of these outer rows of LEDs (i.e., the visibility of the individual LED chips) is typically more apparent from the outside of the lighting fixture. There is less light mixing before the light reaches the tubular housing. Therefore, any scattering or diffusion created by the tubular housing is less effective at hiding the unevenness of the light output from the outer rows of LEDs.

[0036] The level of diffusion or scattering produced by the material of the tubular housing is selected, for example, to achieve a desired visual appearance of the internal structure of the lighting device, particularly obscuring internal design details. A housing with greater transparency is more efficient and allows for better control of the light output distribution, but a more diffusive or scattering housing material will better hide LED unevenness.

[0037] Arranging the outer rows with a smaller pitch (i.e., with the LEDs closer together) reduces unevenness compared to the middle rows, especially for lateral viewing angles. In this way, the overall configuration of the LEDs results in a more uniform light appearance. By arranging the LEDs in this way, with rows of different LED pitches for a given number of LEDs, the overall unevenness of the lighting device is reduced compared to a regular LED array, and more transparent housing materials may be used, allowing better control of the light output distribution.

[0038] Thus, for a given level of unevenness that is deemed acceptable, the light transmission of the tubular housing can be maximized.

[0039] It should be noted that the rows do not have to have a perfectly uniform pitch. Thus, pitches p1 and p2 can be considered to be the average pitch along the length of the row. It should also be noted that there may be more than three rows. For example, there may be two or more intermediate rows. If there are more than three rows, the pitch may gradually increase towards the center of the carrier, or all intermediate rows may have the same pitch.

[0040] The intermediate rows are shown along the centerline of the carrier. If there are two (or any even number) intermediate rows, they may be spaced apart on either side of the centerline. The power distribution is, for example, symmetrical in a plane perpendicular to the length of the elongated carrier.

[0041] Figure 2 shows a cross section perpendicular to the length of the lighting device. Figure 2 shows three rows of LEDs, r1, r2, and r3. Figure 2 shows that the optical path length to the side of the lighting device is shorter for the outer rows r1, r2 than for the inner row r3. This difference in path length causes different visible irregularities for the different rows of LEDs, especially when the lighting device is viewed from the side rather than directly below the lighting device.

[0042] Light emitted from the sides of the lighting device is also outside the main output intensity distribution of the LEDs (e.g., covering an angle of 120 degrees, but with a peak intensity in the perpendicular emission direction). Thus, the light intensity is lower at these steep lateral angles, which also makes the LED structure more visible. Again, this effect is compensated for by the LED pitch selection described above.

[0043] FIG. 2 shows an optional additional feature in which the tubular housing 18 has a wall thickness t1 adjacent the side of the carrier that is greater than the wall thickness t2 facing the LEDs on the carrier, i.e., the wall thickness t2 facing the LED carrier 12.

[0044] This greater wall thickness is therefore provided at the locations of the outer rows of LEDs closer to the wall of the tubular housing, which results in greater scattering by the tube material, thereby further reducing the uniformity of those outer rows of LEDs.

[0045] The thickness of the tubular housing may vary gradually between values ​​t1 and t2, thereby providing a gradual change in thickness depending on the intensity of the LED at different angles.

[0046] The above examples relate to TLED lamps. However, the invention can be applied to any type of linear luminaire with LEDs housed in an elongated housing or simply mounted on an elongated carrier to create a strip of light. Linear luminaires may use lenses or other beam shaping configurations or covers to distribute the light output and do not necessarily need to have a completely surrounding housing such as a tube.

[0047] Variations to the disclosed embodiments can be understood and can be effected by those skilled in the art in practicing the claimed invention, upon study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0048] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0049] It should be noted that when the term "adapted to" is used in the claims or the specification, it is intended to be equivalent to the term "configured to."

[0050] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A long career and an LED arrangement along the length of the elongate carrier; a light-transmitting housing around the carrier; 1. A lighting device comprising: the LED configuration comprises at least first and second outer rows of LEDs extending along the length direction and at least one inner row of LEDs between the first and second outer rows of LEDs, wherein the pitch of the LEDs along the at least one inner row is greater than the pitch of the LEDs along the first and second outer rows, and the light-transmitting housing comprises a tube.

2. The lighting device of claim 1 , wherein the at least one inner row of LEDs is along a centerline of the carrier.

3. The lighting device of claim 1 , wherein the tube has a circular cross-sectional shape.

4. 3. The lighting device according to claim 1 or 2, wherein the tube is made of plastic or glass.

5. 3. A lighting device according to claim 1 or 2, wherein the carrier is mounted against an inner surface of the tube away from a central axis of the tube.

6. 3. A lighting device according to claim 1 or 2, wherein the tube has a wall thickness adjacent a side of the carrier, the wall thickness being greater than a wall thickness facing the LED on the carrier.

7. 3. A lighting device according to claim 1 or 2, wherein the carrier comprises a printed circuit board, and the lighting device further comprises a heat sink to which the printed circuit board is attached.

8. 8. The lighting device of claim 7, wherein the heat sink is aluminum.

9. 3. The lighting device according to claim 1 or 2, wherein the lighting device comprises a tubular LED.

10. 3. The lighting device of claim 1 or 2, wherein the lighting device comprises a linear luminaire.

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