GB2420613A

GB2420613A - Lighting

Info

Publication number: GB2420613A
Application number: GB0419380A
Authority: GB
Inventors: Kenneth Miller
Original assignee: BESPOKE LIGHTING Ltd
Current assignee: COLLINS, MARY
Priority date: 2004-08-27
Filing date: 2004-08-27
Publication date: 2006-05-31
Also published as: GB0419380D0

Abstract

A picture light comprising a circuit and a controller for sending a current to the circuit that changes in polarity, the circuit comprising a first light source which illuminates when current flows though it in a first direction but does not illuminate when current flow through it in the opposing direction, and a second light source which illuminates at least when current flows through it in the opposing direction, wherein the controller is configured to vary the durations for which the current is in the first or opposing directions and/or the amplitude of the current in first direction relative to the current in opposing directions and consequently vary the intensity of the first light source changes relative to intensity of the second light source.

Description

1 2420613 P305556GB Lighting System This invention relates to a light, and

in particular to a light for illuminating a wall mounted picture or other work of art.

Usually, the room which houses paint pictures, paintings or similar works of art will have ceiling mounting lighting such as a strip light or spot lights. However, ambient room lighting such as this is often insufficient to do justice to the art work.

It is usual therefore, particularly in larger rooms such as those commonly found at stately homes, art galleries and museums, to install additional lighting which illuininates the art work in addition to the surrounding ambient lighting. It is known therefore to provide a wall or frame mounted light which illuminates the specific work of art hung on the wall. Such a light serves the purpose of illuminating the work of art to optimise the view of work to the viewer. lt is possible to use lamps or fluorescent light as the light source. However, there are numerous problems with these forms of lighting. In particular they can produce excessive heat or TJV light which may in time deade the illuminated painting.

Such lights normally produce white light, which in many situations may be suitable for ijiuminatiug a painting. However, in other situations it is preferred to have different coloured lighting. Whilst it would be unusual for a strongly coloured lighting such as a specific red or blue light to be used it is frequently desirable to va the exact so called "shade of white" i.e. the extent to which the light is an equal mix of the spectrum or alternatively is loaded towards a particular colour. The colour/shade desired will depend on the particular art work, on the room in which it is located and the effect of any ambient lighting- Changing the shade in this way is currently done by either changing the bulb or by using colour filters. Such filters result in a reduction in light intensity and therefore may have to be accompanied by a more powerful bulb which will generate more beat on the picture. ConsequentlY in order to vary between a large range of shades available it is necessary to have an excessively large nwnber of filters andlor bulbs at great cost to the user.

S If it is desired for example to have a slightly more reddish light than usual then a filter would be used in which much of the non red light is blocked but there is no increase in intensity of the red light in order compensate for this reduction.

It is an object of the present invention to provide an improved light and in particular an improved picture light which allows improved adjustability of colour/shade.

According to the first aspect of the invention there is provided a picture light comprising a circuit and a eonii'oller for sending a current to the circuit that changes in polarity, the circuit comprising a first light source which illuminates when current flows though it in a first direction but does not illuminate when current flow through it in the opposing direction, and a second light source which illuminates at least when current flows through it in the opposing direction, wherein the controller is configured to vary the durations for which the current is in the first or opposing directions and/or the amplitude of the current in first direction relative to the current in opposing directions and consequently vary the intensity of the fit light source changes relative to intensiW of the second light source.

The embodiment of the invention will now be describecL byway of example only, with reference tO the following figures in which: Figure I is a front isometric view of picture lighting in accordance with the present invention; Figure 2 is an exploded isometric view of the picture light of figure 1; Figure 3 is an isometric view of a sub assembly of the present invention including three LED modules; Figure 4 is a schematic circuit diagram of part of the circuit for an LED module of figure3; and Figures 5a, b and c are representations of pulsed current from the controller in figure 3 for use in the circuit of figure 4.

In figure 1 a picture light 10 has a the main body 12 with various support means 14.

The main body 12 contains a light source and has an aperture from which light escapes to be directed onto the painting in use.

With reference to figure 2 it can be seen that thc main housing 12 includes a lighting bus 14.

The lighting bus 14 incoontes a power nil, in the fo of a printed circuit board (PCB) 16, and a number of LED modules 18. The PCB 16 is configured to cooperate with and to be retained within the lighting bus 14.

With reference to figure 3 the PCB 16 defmes copp tracks 20 and 22. The copper tracks 20 and 22 prode electhcal power to each of the LED modules 18. The LED modules 18 are retained within the lighting bus 14 such that they are moveable along the copper tracks 20 and 22 to receive power irrespective of theft position by virtue of the contact with tracks 20, 22.

Each LED module 18 has an LED bank 24 directed towards the aperture of housing unit 12 in order to illuminate the picture in use. The LED module 18 is positioned on the copper track so that it is in communication with relevant circuits printed on the PCB 16.

Each LED bank 24 may contain a number of LEIYs of the same, or different colour.

Alternatively each LED bank 24 may only contain a single LED with the colour varying between the LED modules 18.

in the embodiments described below with reference to figure 4 each bank 24 comprises three LED'S, a red LED 25, a blue LED 26 and a green LED 27. AlternativelY the LED modules 18 can each comprise a single LED with each of the three modules having the red LED 25, blue LED 26 and green LED 27 respectiVely.

Connected to the copper tracks 20, 22 of PCB 16 is a 30. The microcontroller 30 includes an on-chip Pulse width Modulation (PWM) eoniroller. The microcontroller 30 is connected to an AC power supply which it takes as its input, with a pulsed 5V DC signal outputted to PCB 16. Though in figure 3 microcontroller 30 is shown separate from the PCB 14 it can be integrated into the board.

In communication with microcontroller 30 is a an input port 32 such as a USB socket which enables a Personal computer to be connected to the light 10 in order to affect the PWM controller. Alternatively the microcontToller 30 can be incorporated within a customised unit with built in variable controls to enable a user to directly alter the P'Wlvl settings without need for a separate computer.

fiire 4 there is sho a circuit 50 for one of the LED modules iS that is integrated intothePCBl4.

The circuit 50 comprises two terminals 52 and 54 which receive the modulated digital pulses from a controller 30. On the side of terminal 54 the circuit 50 has three parallel branches 56, 58 and 60.

Branch 56 comprises a single path between the terminal 52 and 54, which path includes a diode 62 the red LED 25 and a resistor which shall be referred to as the red light resistor 64 and has a resistance of approximatelY 33 Ohms.

The diode 62 and LED 25 point in the direction from terminal 52 to terminal 54.

ccordingly current in the conventional diagrammatic sense can flow from terminal 52 to terminal 54 and in so doing will generate light from the red LED 25. Current is

S

prevented from flowing through from terminal 54 to terminal 52 by diode 62 and current in this direction will not generate light from the red LED 25.

Branch 58 comprises a single path between terminals 52 and 54. On this path is a diode 68 the blue LED 26 and a resistor; the "blue light resistor" 66. The blue light resistor 66 has a resistance of approximately 2.5 Ohms.

Diode 68 and blue LED 26 are directed towards terminal 57 allowing current through from the terminal 54 to terminal 52 and generating light from the blue LED with current passing in this direction. The diode 68 prevents current from running through the blue light LED from terminal 52 to terminal 54 and light will not be generated from the blue LED 26 by current running in this direction.

Starting from terminal 54, branch 60 initiallY comprises a single circuit path element 61 which runs from tenninal 54 to a junction 61. At junction 67 the branch splits into two alternative paths 70 and 72. Path 70 continueS to a junction 74 where itself splits into two alternative paths 76 and 78. Path 76 continueS directly to terminal 52. Path 78 and path 72 reconnect at junction 80 before onneeting via a single path 82 to terminal 52.

Branch 60 comprises a resistor, the "green light resistor" 69 on path 61, diode 88 on path 70, diode 90 on path 16, diode 92 on path 72 and diode 94 on path 82. Branch 60 also comprises the green LED 27 which is located on path 78. Diodes 94 and 88 are orientated directionallY towards terminal 54 to allow current to flow from left to right whereas diodes 90 and 92 are pointed towards terminal 52 and allow current to flow in the conventional sense from right to left. The green LED 27 is directed towards terminal 54 and will generate light when current flows through it from left to right.

The green light resistor 69 has a resistance of I Ohms.

Current flowing from terminal 54 to terminal 52 will travel along path 61 through the green light resistor 84 to junction 67. Current in this direction will then flow through path 69 but not path 70 due to the opposite directions of diodes 88 and 92. At junction current prevented from reaching terminal 52 via path 82 by the orientation of diode 94. Instead the current flows through green LED 27 to junction 74 and flows through path 76 and diode 90 to the terminal 52. AccordinglY when current flows from terminal 54 to terminal 52, light is generated by green LED 27 and resistors load is S provided by the green light resistor 69.

When current flows from terminal 52 to terminal 54 the current travels through path 82 but not path 76 because of the respective orientations of diode 90 and 92. The current takes the straight path through path 78, 70 and 61 running through LED 27, diode 88 and resistor 69. It is prevented from short circuiting the green LET) 27 along path 72 by the orientation of the diode 92. AccordinglY when current flows from terminal 52 to terminal 54 light is generated by the green LED 27 across a resistance provided by the green light resistor 69.

In summary therefore, current running front terminal 52 to terminal 54 runs in parallel through the red LED 25 and the green LEE) 27 generating light from both. The respective resistor loads are set by red light resistor 64 and the green light resistor 69- The green light resistor is selected so that the intensitY of the red light is approximately double that of the green light. No blue light is generated when the current nins in this directiOn. In contrast when current runs from terminal 54 to terminal 52 no red light is generated but current runs in parallel through blue LED 26 and green LED 27- Due to the resistance of blue light resistor and the green light resistor the intensity of the blue light generated in this direction is approximately double that of the green light generatedIn figures 5k. SB and SC are shown three examples of pulse trains generated by the microcOntroller 30.

Referring to figure 5A there is shown a standard setting of pulse width modulation whereby the pulses are all of equal width and alternate between positive and negative width equal durations through both. The current of this wave can be sent through circuit 50.

Where the pulse is positive such as at 70, 74 current flows from terminal 52 to terminal 54 and therefore no blue light is generated and twice as much red light generated as green. Whenever the pulses are negative such as at 76 and 78 then the current flows from terminal 54 to terminal 52 such that no red light is generated and twice as much blue light is generated as green- Preferably the frequency is sufficiently high such as Hertz in operation such that the output which is projected on to a picture in use is seen as white light. This occurs since whilst both the red light and blue light switch on and off the flicker is too quick for the hunian eye to appreciate.

With the wave form shown in Figure SA equal intensities of red, blue and green are produced thereby forming white light. This happens since whilst the green light is produced at half the intensity of the red or blue it is generated for total double the duration and therefore the total intensity will be the same as the red or blue over an is appreciable period.

Refeing to figure SB there is sho a second wave form. The pulses are unequal width such that for each positive duration 170, 172 the pulses are short whereas when the pluses are negative such as 118 the durations are approximately twice as long.

The green LED 27 is unaffected by the direction of the current and therefore continues at the same intensity whatever the wave form. In contrast the red and blue are dependent and in this instance the blue will be on for a total duration double that of the red LED. The new pulse pattern therefore changes the shade of colour produced significantly to be bluer since the intensity of blue light is twice as high as the intensity of red light generated. Notably variation in shade produced by altering the intensity of the light sources by modulation does not require any change to the resistorS 64, 66 and 84 a and therefore no more heat has to be dissipated by them collectively, lids is considered very important in picture applications where heat can be damaging to paintings.

Figure 5C shows a third pulse modulation which can be produced by controller 30. In this example the positive pulses 270, 274 are three times as long as the pulses negative side such as 276 and 278. ConsequentlY the intensitY of the red light will be three times as much as the intensity of the blue light whilst the intensity of green light will be unaffected. The light emitted will be significantly redder.

A computer connected to port 32 is able to change the pulse modulation of the controller to generate pulses of any width and accordingly any range of intensities of red and blue light can be generated. Whenever the red light is reduced the blue light will increase intensity to compensate so that the intensity of the total light is the same, and vice versa when the blue light is reduced. It has been surprisingly found that by keeping the green light constant whilst altering only the red and blue, virtually the entire range of desired shades can be achieved despite one primarily colour (green) never being adjusted. dvntge0U5lY therefore the user merely has to increase or decrease the redness with a corresponditig increase or decrease the blue being produced and does not have to adjust the green. This simplifies the options available to the user as well as reducing the number of and complexity of components need in circt 50 helping to minimise heat generation but still maintaining the range of shades needed and requfred for displaying art.

Beneficially the resistors 64, 66 and 84 can be of very small resistance and therefore dissipate very little heat since they are only needed to maintain ratios of current between the three LED's 24, 25 and 26. No variations in resistance is needed to vary the amount of the intensity of the sources and therefore no significant change in the heat is required for this adjusirnent. The only change will be from the amount of heat generated by the LED through the increase in duration of current running through it, but LED's themselves produce little heat.

It can be seen that the arrangement of diodes for branch 60 is in effect a Ml wave rectifier since the same amount of current continuously passes through green LED 27 for both negative and positive parts of the wave.

Claims

Claims 1. A picthrC light comprising a circuit and a controller for

sending a current to the circuit that changes in polaritY the circuit comprising a first light source which illuminates when current flows though it in a first direction but does not illuminate when current flow through it in the opposing directions and a second light source which illuminates at) east when current flows through it in the opposing direction, wherein the controller is configured to vary the durations for which the current is in the first or opposing directions andior the amplitude of the current in first direction relative tO the current in opposing directions and consequently vary the intensity of the first light source changes relative to intensity of the second light source.

2. A picture light according to claim 1 in which the controller is a pulse width modulation controller for sending pulsed DC current to the circuit and wherein is variation of the durations for which the cuirent is in the first or opposing directions is caused by modulation of the pulse widths.

3. A picture light according to claim 2 wherein the second light source does not illuminate when current flows in the first direction, so that increasing the intensity of the first light source by modulating the pulse widths decreases the intensity of the second light source and decreasing the intensity of the first light source by modulating the pulse widths increases the intensity of the second light source.

4. A picture light according to any preceding claim wherein the circuit comprises a third light source which illuminates at least when current flows through it in the opposing direction.

5. A picture light according to claim 4 wherein the third light source illuminates when current flows though it in either direction.

6. A picture light cordir'g to claim 5 wherein the third light source illuminates at the same intensity regardless of the direction of current and is therefore unaffected by variations in pulse width.

7. A picture light according to any preceding claim wherein the light sources in the circuit are connected in parallel.

8. A picture light according to claim 6 and 7 wherein the circuit comprises a fill wave rectifier in series with the third light source which provides the tbird light source with its current direction independence.

9. A picture light according to any preceding claims wherein one or more of the light sources is an LED.

10. A picture light according to any preceding claim wherein all of the light sources are LED'S.

11. A picture light according to any preceding claim wherein the third light source is an LED, and the circuit comprises Ibur diodes all in series with the third light source, two of the diodes only allowing current to pass in the first direction and are in series which each other and with the third light source, providing a first circuit path through the third light source allowing current in the first direction to pass through the LED in the correct direction tO cause illumination; the other two diodes only allow current to pass in the opposing direction and are in series which each other and tire third light source but in parallel with the first two diodes, the other diodes forming part of a second circuit path through the third light source allowing current in the opposing direction to pass through the LED in the correct direction to cause illumination 32. A. picture light according to arty preceding claims wherein the first light source produces only red light.

13. A picture light according to any preceding claims wherein the second light source produces only blue light.

14. A picture light according to any preceding claims wherein the third light source produces only green light 15. A picture light according tO ay preceding claim wherein the resistive loads of the parallel branches the circuit which respectively contain the first and second light sources are 5tantiaily equal so that if equal pulse width are generated by the controller with equal length pulses in the first and opposing current directions the intensity of light generated by the first and second light sources is approximatel)' the same.

16. A picture light according to any preceding claim when dependent on claim 4 wherein the resistive load of the parallel branch of the circuit ntaining the third light source is approximately double the resistive load of the branch containing the first light source so that if equal pulse widths are generated by the controller with equal length pulses in the first and opposing current directions the intensity of the first and third light sources is approximately the same 17. A picture light according to any preceding claim where if equal pulse widths are generated by the controller with equal length pulses in the first and opposing current directions the light from the light sources llectively produce white light 18. A picture light according to any preceding claim where the light comprises a communication port connected to the controller for connection to a computer to instruct the controller to modulate the pulse widths.

19. A picture light according to any preceding claim where the light comprises an input device such as a keypad connected to the controller allowing a buman user to instruct the controller via the keypad to modulate the pulse widths.

20. A picture light according to claims wherein the LED or LED's are selected to eliminate ultraviolet light.

21. A picture light according to any preceding claim wherein the light sources form part of an LED module and preferab1y wherein the LED module is retained in a lighting bus.

22. A light assembly comprising a circuit and a controller for sending a current to the circuit that changes in polarity, the circuit comprising a first light source which illuminates when current flows though it in a first direction but does not illuminate when current flow through it in the opposing direction, and a second light source which illuminates at least when current flows through it in the opposing direction, wherein the controller is configured to vary the durations for which the current is in the first or opposing directions and]or the amplitude of the current in first direction relative to the current in opposing directions and consequently vary the intensity of the &st light source changes relative to intensity of the second light source.

23. A light assembly according to claim 22 further comprising any of the addiüonal features defined in any of dependent clthms 2 to 21.

24. A picture light for illuminating a picture in white light comprising a red light source, a blue light source and a een light source which together can produce the white light, the picture light further comprising means for varying the intensity of the red light source, means for varying the intensity of the blue light source and means for keeping the green light source at a constant intensity.