GB2497875A - LED lighting unit - Google Patents

Abstract

A light emitting diode lighting unit has longitudinal and transverse axes and comprises a base 12 extending along the longitudinal axis. A partial diffuser 20 has diffusion bands and clear bands each extending along the longitudinal axis of the lighting unit arranged in an alternating pattern across at least a part of the transverse axis of the lighting unit. A plurality of LEDs 14A, B, C are located along the longitudinal axis of the lighting unit such that respective transverse positions of at least a subset of the LEDs are different to the transverse positions of respective neighbouring LEDs.

Description

LED LIGHTING UNIT

The present invention relates to an LED lighting unit.

LEDs are increasingly used in commercial applications to create white light. This is due to their being more efficient than conventional light sources and having a longer service life. The initial cost of LEDs is comparatively high but LED costs are falling as volumes increase, while costs of conventional lamp technologies such as fluorescent and metal halide are rising. It is anticipated that virtually all new lighting will usc LED sources within 10 years.

Glare is an unwanted effect of lighting where a user's vision is adversely affected by objects that they perceive as being too bright. Glare is generally caused by two adjacent objects having very different brightnesses: A 100w light bulb seen against a white ceiling has subjectively less glare

than one viewed against a dark background.

Glare is often considered to occur where one surface has a brightness, measured in Candelas per Meter Squared (cd/m2), that is more than 10 times that of an adjacent surface.

A typical individual LED produces 100 lumens of light from a very small light emitting surface -typically 3mm x 5mm i.e. 15x106 m2. This creates a light intensity of more than 1,000,000 cd/m2. By contrast, a conventional T8 fluorescent tube has a surface brightness of just 10,000 cd/m2. Hence typically an individual LED is 100 times brighter than a fluorescent tube over the same surface area.

Consequently it can be expected that if a light is designed such that the LEDs are directly visible then there are likely to be problems with glare.

Existing solutions to this problem all seek to increase the effective radiating surface of the light, so that the brightness per metre squared is reduced. Hence installing a diffuser in front of the LEDs so that the light is spread out over a larger area reduces glare, but has the disadvantage that the diffuser absorbs light and so reduces overall efficiency.

An alternative solution is to aim the LEDs away from the user and reflect the light from a larger surface. However this similarly reduces efficiency as the reflector will also absorb light.

In another solution, for ceiling mountcd lights the LEDs are shielded from view beyond a certain angle so that glare will only be perceived if people dclibcrately look up into thc light. However, aiming all the light downward in this way creates unwanted shadows, dark walls and dark ceilings, which in many environments are undesirable.

Hence it is desired to produce a light that has improved overall efficiency compared to standard diffusers, reduces glare compared to a naked LED, and provides a broad lighting angle.

The present invention seeks to address or mitigate this desire.

In a first aspect, an LED lighting unit is provided in accordance with claim 1.

Further respective aspects and features of the invention are defined in the appended claims.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1A and I B are respective plan and cross-sectional schematic diagrams of an LED strip-light.

Figures 2A and 2B are respective plan and cross-sectional schematic diagrams of an LED lighting unit in accordance with an embodiment of the present invention.

Figures 3A and 3B are respective plan and cross-sectional schematic diagrams of an LED lighting unit in accordance with an embodiment of the present invention.

Figure 4 is a plan schematic diagram of an LED lighting unit in accordance with an embodiment of the present invention.

Figure 5 is a flow diagram of a method of manufacturing an LED lighting unit in accordance with an embodiment of the present invention.

An LED lighting unit is disclosed. In the fbllowing description, a number of specific details are presented in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to a person skilled in the art that these specific details need not be employed to practice the present invention. Conversely, specific details known to the person skilled in the art are omitted fur the purposes of clarity where appropriate.

Referring to Figures 1 A and 1B, which respectively show the plan and cross-sectional views of a strip-light style lighting unit, a hybrid solution combining features of the diffuser and the shielded LEDs mentioned previously may be envisaged that is suitable fur LED lighting units, and in particular fur LED strip-lights intended to replace fluorescent tubes.

In these Figures, a lighting unit 10 comprises a partial diffuser 20 comprising in turn diffusion bands 22 and clear bands 24. In an embodiment of the present invention the diffusion bands are translucent and operate in the conventional manner of a diffuser, and may be formed for example by selectively frosting the surface of the partial diffuser, or applying strips of a suitable diffusing material to a transparent substrate The clear bands are thus transparent and absorb less light than the diffusion bands. The diffusion bands and clear bands each extend along a longitudinal axis of the lighting unit and, as shown in Figure 1, are arranged in an alternating pattern across at least a part of the transverse axis of the lighting unit. Typically the clear bands are equally spaced.

It will be appreciated that whilst the clear and diffusion bands may be made of glass and/or plastic, similar functionality can be obtained for example using diffuser bands made of perforated metal strips (where diffusion occurs for example due to diffraction through the perforations), typically made from sheet metal 0.4 -1.2mm thick. Such a perforated metal strip may be mounted on a transparent substrate (glass or plastic) or may be strong enough to not require a substrate (or just require periodic support), in which case the clear bands of the partial difThser may optionally simply be gaps between the perforated metal diffusion bands. Such a metal-only arrangement may be more suitable for outdoor ancL/or security lighting applications.

In any event, the partial diffuser can therefore allow some direct light from the LEDs 14 to be projected downward, with greater efficiency compared to the diffuser bands, whilst diffusing the outward facing light to limit glare at more acute viewing angles.

However, the alternating clear bands and diffusion bands can result in visible bands of brighter light (34A,B,C) and darker light (32A,B,C) being projected onto a surface (typically the floor).

This is unsatisfactory, as a more uniform illumination is typically desired.

Consequently in accordance with an embodiment of the present invention, and referring to Figures 2A and 2B which respectively show plan and cross-sectional views of a lighting unit 10', then an LED lighting unit such as a strip-light has a longitudinal axis and a transverse axis, and comprises a base 12 extending along the longitudinal axis of the strip light. The partial diffuser comprises diffusion bands and clear bands as described previously, each extending substantially along the longitudinal axis of the light and arranged in an alternating pattern across at least a part of the transverse axis of the light.

It will be appreciated that the transverse extent of the ahernating bands in conjunction with the distance of the bands from the LEDs determines the angular range under the light within which some direct light will be perceived by users. Hence different widths of partial diffuser may be provided for different uses of lights, with for example lights to be positioned on high shop ceilings having a smaller width of alternating bands than lights for use in domestic housing with lower ceilings.

A plurality of LEDs are then located along the longitudinal axis of the strip light, for example by being attached to the base. In an embodiment of the present invention, the base is (or comprises) a printed circuit board (PCB) comprising the electrical connections and holes required by the LEDs, and hence the LEDs may be directly inserted into the base in connection with a suitable electrical circuit for illumination. in another embodiment, the LEDs may be electrically connected independently of the base and simply use the base for mechanical support (e.g. the base may simply provide holes for the LEDs), or any mix of the two. A typical strip-light may comprise as a non-limiting example 20 to 200 LEDs, and in typical embodiments common strip-light lengths may comprise 84 or 168 LEDs.

The LEDs are generally evenly spaced along the longitudinal axis of the light.

However, in an embodiment of the present invention, the transverse positions of at least some of the LEDs on the transverse axis are different to those of their neighbours.

In Figure 2A, the transverse positions of the LEDs are shown to progress across the width of the partial diffuser, so that the LEDs appear to be positioned diagonally with respect to the partial diffuser.

Referring now to Figure 2B, for clarity only 3 of the 20 to 200 LEDs are again shown at positions on the transverse axis of the strip light that progress across the width of the partial diffuser. Arrows from the three LEDs 14A,B and C illustrate that for this arrangement there is no longer clear regular banding on the floor, because the different positions of each LED with respect to the clear and diffuse bands in the partial diffuser means that each LED casts its own light and dark banding onto the floor at correspondingly different positions; these different light and dark bands therefor tend to cancel each other out, resulting in a more even illumination.

As noted above, in Figures 2A and 2B, the LEDs are shown in a linear arrangement across the diagonal of the partial diffuser. Whilst this arrangement is relatively easy to implement, the apparent misalignment of the line of LEDs to the line of the lighting unit and the partial diffuser can look accidental and unsightly to a user unaware of the purpose of the LED positioning.

Consequently, referring now also to Figures 3A and 3B which respectively show plan and cross-sectional views of a lighting unit 10" according to an embodiment of the present invention, then in this case the transverse positions of at least a subset of the LEDs are randomised.

As can be seen in Figure 3B, arrows from the three LEDs 14A,B and C illustrate that again there S is no longer regular banding on the floor, because the banding generated by each LED is now substantially uncorrelated with the banding cast by neighbouring LEDs. The cumulative effect of these uncorrelated bands is again to substantially cancel each other out and generate a subjectively even light on the floor.

In this case however, the randomised transverse position of at least some ofthe lights means that there is no longer an apparent misalignment of a linear sequence of LEDs in the lighting unit when observed by a user.

It will be appreciated that in either the case of the diagonal line of LEDs or the at least partially transversely randomised sequence of LEDs described above, this still results in a lighting unit in which within the selected angle below the lighting unit the illumination is overall brighter due to the clear bands of the partial diffuser than an equivalent standard LED strip-light using a standard diffuser.

In this way, advantageously the lighting unit in the above embodiments is more efficient than a standard LED lighting unit in terms of overall brightness due to the clear bands, but still reduces glare relative to a naked LED, and still provides a broad lighting angle due to the diffuser regions on either side of the banded region; and does this without generating a noticeable banding pattern on the illuminated surface.

With regards to a randomised sequence of LEDs, in an embodiment of the present invention the randomised distribution is a uniform randomised distribution on the transverse axis of the lighting unit (e.g. the strip-light. ]n other words, there is a substantially equal probability of an LED being positioned anywhere within a predetermined width across the transverse axis of the lighting unit. In an embodiment of the present invention, that width is equal to the width between the first and last clear bands of the partial difftiser. In another embodiment, it is equal to the width of N times the pitch between the clear bands of the partial diffuser, where N is between one and the total number of clear bands. In another embodiment of the present invention, that width is equal to the width across which LEDs can be mounted on the base (assuming that this is different to the other widths described above). Other suitable widths may be selected by a designer of a light as appropriate to the use of the light (for example responsive to the expected height of deployment of the light, as noted previously).

In another embodiment of the present invention, the randomised distribution is a Gaussian randomised distribution, bounded by the predetermined width across the lighting unit. It will be appreciated that the variance of the Gaussian distribution will affect how the LEDs cluster around a centreline. Hence for example a lighting unit in which the effective variance permits one standard deviation within the predetermined width will have more LEDs closer to the centreline than an equivalent light with a 1⁄4 standard deviation within the predetermined width.

Hence the line of LEDs in Figure 2A and the distribution of LEDs in Figure 3A can be considered to lie on a continuum of LED arrangements determined by thc variance of a Gaussian distribution along some or all of the diagonal line.

In another embodiment, rather than treating the randomisation as being across the transverse axis, the randomisation can be treated as occurring along a portion of the longitudinal axis. In this embodiment, the operating width of the base (i.e. the width of that portion of the base upon which LEDs are to be placed, for example as defined previously herein) is equally divided into M lines, where M is the number of LEDs in a predetermined length of the lighting unit. Hence for example M may be 14. One LED is positioned on each line, but at a random or pseudo-random position along it on the longitudinal axis. A resulting random or pseudo-random pattern of LEDs having a roughly uniform randomised distribution can then be selected for that predetermined length of the lighting unit to form a section. Sections comprising that pattern can then be rcpeated to form the desired length of strip-light. If it is desired to increase the overall brightness of the lighting unit, then more than one LED can be positioned on one or more of the lines, and thcn each is given a random longitudinal position.

It will be appreciated that the overall effect is similar to that of the transverse randomisation described previously, in that for a longitudinal progression along the strip-light the transverse positions of at least some of the LEDs will be uncorrelated.

It will be appreciated that in either case (transverse or longitudinal randomisation), the random pattern need only be generated once, and may then be repeated for each subsequent lighting unit or section thereof. It is not necessary that the LEDs in any one lighting unit are in a uniquely random configuration with respect to any other lighting unit.

It will also be appreciated that whether the LEDs are positioned randomly in the transverse direction at regular longitudinal intervals, or positioned randomly in the longitudinal direction at regular transverse intervals, as per the embodiments above, the resulting lighting unit in both cases can be described as having a pattern comprising different transverse positions for successive LEDs along the longitudinal axis of the lighting unit.

As noted above, in practice the random positioning of LEDs may be implemented under some form of computer control, such as with a standard surface-mount printcd circuit board device, which will position thc LEDs in the lighting unit -for example on the printed circuit board forming some or all of the base 12. Consequently in an embodiment of the present invention the randomised transverse positions of the LEDs are a pseudorandom pattern generated in accordance with a predetermined rule, implemented by the computer, or are such a pattern prepared in advance and then stored on the computer. As noted above, the rule may be responsive to a variance or standard deviation value as applicable. Such pseudorandom number generators are known in the art and are not discussed further here.

As noted above it will be appreciated that it is not necessary to randomise each instance of the lighting unit differently; a pattern comprising different transverse positions for successive LEDs can be predetermined, for example using a pseudorandom pattern as described above for some or all of the LEDs, and this pattern can be used for each copy of the lighting unit or section thereof In particular, in an embodiment of the present invention the printed circuit board base 12 may be fabricated according to this predetermined pattern or a repeated sequence thereot so that circuit tracks and component holes are at corresponding positions for the LEDs.

Hence, in an embodiment of the present invention, a printed circuit board suitable for use in the LED lighting unit has a longitudinal axis and a transverse axis (e.g. for a strip-light form factor), and comprises a plurality of pairs of holes for accommodating respective LEDs located along the longitudinal axis of the lighting unit, and electrical connections servicing the respective pairs of holes (for example conductive tracks located sufficiently close to the holes to enable electrical contact upon soldering the LEDs to the printed circuit board), and wherein the respective transvcrsc positions of at least a subset of the pairs of holes are different to the transverse positions of respective neighbouring pairs of holes on the printed circuit board, in a corresponding manner to that described for the LEDs themselves herein.

The surface-mount printed circuit board device then positions the LEDs in the holes according to the same predetermined pattern.

It will be appreciated that not all of the LEDs in a lighting unit need to be randomised using one of the above described techniques; rather this is preferred because it both improves the appearance of the lighting unft and also because uncorrelated banding from randomly positioned LEDs will tend to cancel out more quickly (i.e. require fewer overlapping bands from correspondingly fewer LED5) than banding from partially correlated LEDs such as those of Figures 2A and 2B.

Hence more generally neighbouring LEDs should simply have different transverse positions so as to generate banding on the illuminated surface at correspondingly different positions, so that the overall illumination of the surface becomes subjectively even. The proportion of LEDs whose transverse position is substantially uneorrelated with a neighbouring LED (i.e. randomised) may then be increased to make the lighting source look more regular and to reduce the potential for residual banding effects on the illuminated surface.

Hence for a lighting unit in which neighbouring LEDs have different transverse positions, the proportion of randomly transversely positioned LEDs amongst those LEDs may be] 0%, or more preferably 20%, or more preferably 30%, or more preferably 40%, or more preferably 50%, or more preferably 60%, or more preferably 70%, or more preferably 80%, or more preferably 90%, or more preferably 100%, with a corresponding increased randomness in the projected banding in the illuminated surface ifirther improving the uniformity of the light.

Hence for example a linear sequence of LEDs non-parallel to the longitudinal axis of the lighting unit (as in Figure 2A) may be interspersed with randomly transversely positioned LEDs, or as noted above a transversely randomised pattern of LEDs may repeat after a suftable distance.

It will be appreciated that by chance some LEDs may be located at the same transverse posftion within the lighting unit, but that in general neighbouring LEDs will not have the same transverse position. Finally, if pairs of LEDs are mounted together, these can be treated as single LEDs (or single light sources) for the purpose of the above techniques, so that such LEDs are randomised or otherwise transversely re-positioned on a pairwise basis.

Thus more generally at least one subset of the LEDs may be respectively randomly positioned on the transverse axis of the lighting unit, and this or these subsets may be contiguous or non-contiguous, or a mix of both.

Referring now to Figure 4, this figure illustrates a dual lighting unit 10" according to an embodiment of the present invention having the form factor of a strip-light, and comprising 168 LEDs. The LEDs are mounted on eight printed circuit boards as shown collectively forming a base for two rows of LEDs. Hence in this case the lighting unit is equivalent to a lighting unit with two fluorescent tubes mounted lengthwise side by side. It would appreciated that onc equivalent strip-light would therefore comprise 84 LEDs.

The first row comprises 84 LEDs, formed by a first PCB 12A having 14 LEDs, a second and third PCB 12B,C having 2x14 LEDs and a fourth PCB 12D having 14 LEDs. The second row is the same as the first. These PCBs thus form blocks of two lengths, from which strip-lights may be constructed in a modular fashioa.

The blocks have randomised patterns as described herein. Notably there are several positions on each block where there are two LEDs at the same longitudinal position. In these cases, the additional LED is separately provided for emergency lighting purposes.

In an embodiment of the present invention the remaining LEDs are arranged to have different transverse positions to their neighbours as follows: A pattern for a set of 14 LEDs successively offsets them over a predetermined width, such as for example 20mm, to transversely offset each by width! No. LEDs, so in this case 20/14=1.5mm to form an interim diagonal pattern.

Then 6 of the 14 LED positions were moved transversely by a pseudo random amount within the predetermined width to generate a non-linear effect in the final pattern. It will be appreciated that the pseudo random amount may have a finite granularity, e.g. the same offset step (in this

example 1.5mm).

A pattern for a set of 2x14 LEDs comprises a repeat of the pattern for the 14 LEDs, but with the first instance of the pattern shifted transversely by half the offset determined for the 14 LED pattern (i.e. in this example by 0.75mm). The second instance of the pattern is shifted transversely in the other direction, again by 0.75mm, so that the total transverse offset between the two versions of the pattern are again 1.5mm.

Of course it will be appreciated that patterns and block sizes may be selected as appropriate to a designer's needs according to any of the principles described herein.

In an embodiment of the present invention, the partial diffuser for each lighting unit comprises 8 narrow clear bands spaced 10mm apart (not shown).

Hence the predetermined transverse width limited to be an integer multiple of the pitch (distance) between the clear bands, in this case a multiple of two.

Finally, in an alternative embodiment of the present invention, the partial diffuser operates as a partial baffle. In this case the structural arrangement is overall similar to that of the partial diffuser described above, but rather than having diffusion bands 22, the baffle bands are opaque.

Similarly to the extent that the sides of the partial diffuser have a diffusion surface, on a partial baffle they would be opaque. Thus a partial baffle limits the angle of illumination to a limited angle below the light, with the baffle bands performing a similar function to the diffusion bands of limiting glare from the LEDs housed within. Meanwhile the LEDs are arranged at least partially in an uncorrelated fashion as described previously herein.

Typically such a partial baffle would be constructed of metal fbr durability, though of course an opaque plastic or ceramic or other suitable material may be used. Typically the clear bands of the partial baffle are simply gaps between the baffle material, but may be formed from plastic or glass, such as a toughened safety glass.

Rcfbrring now to Figure 5, in an embodiment of the present invention a method of manufacturing an LED lighting unit, such as a unit having strip-light fbrm fictor, and having a longitudinal axis and a transverse axis, comprises: -In a first step slO, sequentially positioning LEDs longitudinally along the lighting unit base; -Wherein the step of sequentially positioning LEDs longitudinally along the lighting unit base comprises the sub-step s12 of positioning at least a subset of the LEDs at a respective transverse position different to the transverse position of a respective neighbouring LED.

It will be apparent to a person skilled in the art that variations in the above method corresponding to operation of the varions embodiments of the apparatus as described and claimed herein are considered within the scope of the present invention, including but not limited to the respective transverse positions of at least a subset of the LEDs being substantially uncorrelated with the transverse position of their immediately neighbouring LEDs As noted above, the LEDs will typically be positioned by a standard surface-mount printed circuit board device operating under software control to carry out the above method.

Consequently, it will be appreciated that the methods disclosed herein may be carried out on conventional hardware suitably adapted as applicable by software instruction or by the inclusion or substitution of dedicated hardware.

Thus the required adaptation to existing parts of a conventional equivalent device may be implemented in the form of a non-transitory computer program product or similar object of manufacture comprising processor implementable instructions stored on a data carrier such as a floppy disk, optical disk, hard disk, PROM, RAM, flash memory or any combination of these or other storage media, or realised in hardware as an ASIC (application specific inteated circuit) or an FPGA (field programmable gate array) or other configurable circuit suitable to use in adapting the conventional equivalent device. Separately, if applicable the computer program may take the fbrm of a transmission via data signals on a network such as an Ethernet, a wireless network, the Internet, or any combination of these or other networks.

Claims (1)

1. <claim-text>CLAIMS1. A light emitting diode (LED) lighting unit having a longitudinal axis and a transverse axis, comprising: a base extending along the longitudinal axis of the lighting unit; a partial diffuser comprising diffusion bands and clear bands each extending along the longitudinal axis of the lighting unit and arranged in an alternating pattern across at least a part of the transverse axis of the lighting unit; and a plurality of LEDs located along the longitudinal axis of the lighting unit; andwherein the respective transverse positions of at least a subset of the LEDs are different to the transverse positions of respective neighbouring LEDs of the lighting unit.</claim-text> <claim-text>2. An LED lighting unit according to claim 1, in which the transverse positions of at least a subset of the LEDs are randomised.</claim-text> <claim-text>3. An LED lighting unit according to claim 2, in which the LEDs have a distribution selected from the list consisting of: a uniform randomised distribution on the transverse axis of the lighting unit; and ii. a Gaussian randomised distribution on the transverse axis of the lighting unit.</claim-text> <claim-text>4. An LED lighting unit according any one of the preceding claims in which the distribution of the LEDs on the transverse ax[s of the lighting unit is limited to a width that is an integer multiple of the distance between two clear bands of the partial diffuser.</claim-text> <claim-text>5. An LED lighting unit according to any one of the preceding claims, in which the transverse positions of at least a subset of the LEDs are a pscudorandom pattern generated in accordance with a predetermined rule.</claim-text> <claim-text>6. An LED lighting unit according to any one of the preceding claims, in which the lighting unit has a strip-light form factor.</claim-text> <claim-text>7. An LED lighting unit according to claim 6, in which the lighting unit comprises a longitudinal sequence of between 40 and 200 LEDs.</claim-text> <claim-text>8. An LED lighting unit according to any one of the preceding claims, in which the respective transverse positions of at least a subset of the LEDs, being different to the transverse positions of respective neighbouring LEDs of the lighting unit, thereby form a pattern; and that paftem is repeated along the length of the LED lighting unit.</claim-text> <claim-text>9. An LED lighting unit according to any one of the preceding claims, in which the partial diffhser is constructed from one or more selected from the list consisting of i. glass; and ii. plastic 10. An LED lighting unit according to any onc of the preceding claims, in which the partial diffuser is constructed from perforated metal.11. An LED lighting unit according to any one of the preceding claims, in which the partial diffuser operates as a partial baffle, having opaque dififision bands.12. An LED lighting unit substantially as described herein with reference to the accompanying drawings.</claim-text>