GB2471836A

GB2471836A - Light emitting diode apparatus having a predetermined spectrum of wavelengths

Info

Publication number: GB2471836A
Application number: GB0911941A
Authority: GB
Inventors: Frank Trebes
Original assignee: NEOPHOS DEV Pte Ltd
Current assignee: NEOPHOS DEV Pte Ltd
Priority date: 2009-07-09
Filing date: 2009-07-09
Publication date: 2011-01-19
Also published as: WO2011004019A1; GB0911941D0

Abstract

A lighting apparatus for lighting a room with a light having a predetermined spectrum of wavelengths. The lighting apparatus comprises a plurality of positions to place light-emitting diodes, LEDs, 101 to 111 and a plurality of light-emitting diodes 2. A first subset of the plurality of light-emitting diodes, 101 and 111, emits light of a first colour and a second subset of the plurality of light-emitting diodes, 102 to 110, emits light of a second colour. The spectrum of the first colour is closer to the spectrum of the predetermined spectrum than the spectrum of the second colour to the predetermined spectrum. The light-emitting diodes of the first subset are placed such that at outer positions of the apparatus and the light-emitting diodes of the second subset are placed at the inner positions of the apparatus.

Description

Lighting apparatus for rooms The invention relates to a lighting apparatus for rooms. Ar- tificial light in rooms often leads to an unpleasant impres-sion of the light. Light bulbs and fluorescent tubes emit light that make objects and the skin of humans look pale. It is known that light-emitting diodes may be used to emphasize the colours of objects, e.g. fruits in convenience stores.

However, the use of these diodes is restricted to certain colours. Improvements to the spectrum of artificial light are desirable.

According to the invention, a lighting apparatus for lighting a room with a light having a predetermined spectrum of wave-lengths is provided. The lighting apparatus has housings with a plurality of positions to place light-emitting diodes. The lighting apparatus further has a plurality of light-emitting diodes that are placed in the positions of the housing. A first subset of the plurality of light-emitting diodes emits light of a first colour and a second subset of the plurality of light-emitting diodes emits light of a second colour. The spectrum of the first colour is closer to the predetermined spectrum than the spectrum of the second colour to the prede-termined spectrum. The light-emitting diodes of the first subset are placed at the outer positions of the apparatus and the light-emitting diodes of the second subset are placed at the inner positions of the apparatus.

Each LED comprises not one wavelength but a spectrum around its dominant colour. One of the possible colours is white be-cause blue LED's with a yellow coating emit white light. The spectrum of an LED to be closest to the predetermined spec- trum is understood as having a good overlap between predeter-mined and dominant spectrum. The holding comprises outer and inner positions. The outer positions are understood as to be the positions having the largest distance to the centre of the holding.

If the spectrum is close, the correlation factor between the spectrums x(A) and yl(A) is large. The correlation factor is calculated by the following formula: J x(2)vl(A)dA rhol= x2(2)dA *J y12(A)d2 whereby A is the wavelength in nm.

The lighting apparatus provides a light that gives an impres-sion of only one colour even though the colour results from mixing at least two colours. This makes it possible to gener-ate light with desired colours without being restricted to the colours that lamp bulbs or single LED types originally provide. However, it is essentially that the outer positions are filled with LED's of a colour being closest to the prede- termined spectrum. Otherwise, the light would look non-uniformly with clearly distinguishable colours other than the predetermined spectrum. It is believed that a colour at the outer positions is not completely mixed because, at the edges of the light cone emitted by the lighting apparatus, the light of the outer LED's misses at the outer ends light from other LED's.

As discussed above, artificial light often makes objects look pale. One of the reasons is that the spectrum provided by ar-tificial light misses specific wavelengths. E.g. artificial light often misses wavelengths for red light. By contrast, the spectrum of daylight emitted by the sun comprises these wavelengths including red. By combining a plurality of LED's having different wavelengths, LED's emitting red light may be included. Thus, the emitted light of the lighting apparatus comprised red light, which makes e.g. the skin of humans look more natural. Further, if a lighting apparatus is used in convenience stores to light fruit, the same lighting appara-tus may be used to light green lettuce as well as the meat, because the lighting apparatus may include green LED5 as well as red LED5, which provide the wavelength to emphasize the natural colour of the respective objects.

In an embodiment of the lighting apparatus, the arrangement of the colours of the light emitting diodes is axis- symmetrical. This ensures that the light is equally distrib-uted and mixed in the room.

Preferable the number of light-emitting diodes is odd, also ensuring a uniform distribution of the light.

Providing the positions of the housing in form of a row makes it possible to fix the lighting apparatus on a bar. Such bars are inconspicuous when distributed in rooms.

Alternatively, the positions for light-emitting diodes are placed concentrically. With this measure, the lighting appa-ratus may be fitted in a conventional lamp holder for a bulb lamp.

The distance d between neighboured light-emitting diodes preferably holds the following condition: 5mm < d < 30 mm, preferably d < 20 mm. A shorter distance would lead to insuf-ficient heat dissipation, whereas a distance larger than 30 mm would mean that the light of the light cones do not suffi-ciently mix. An observer would get the impression that there is plurality of light sources having different colours.

Neighbour is understood as following: Neighbours of one LED are LED's that have the shortest distance to the one LED. An LED may have one neighbour or a plurality of neighbours. The distance is measured from the centre of the light-emitting part of the LED.

If the light cone of each of the light-emitting diodes has an opening angle of 160 and 170 degree, the light is broadly distributed without the need of a further optical apparatus like a lens. In an alternative embodiment, a lens is provided to focus the emitted light of the LED's.

In a further embodiment, each light-emitting diode is hold in a holder forming an opening, whereby upper part of the light-emitting diode is 0 mm to 1mm lower than opening end of the holder. This ensures that the light cones are completely mixed.

To summarize, eleven to twenty-one LED's are combined by placing them as close as possible together. The LED's produce a light that is well mixed and as homogeneous as possible.

The LED module formed by these LED's is arranged in a lamp such that the LED's are not visible. The actual lighting of the room is done via reflections from walls and ceilings. The lamps may be mounted in short distance to an object to be il-luminated, because the light source is not visible to the user and does not damage the object due to the low power con- sumption as well as by not emitting ultra-violet resp. infra-red light.

In an embodiment, lenses are provided to change the angle of the emitted light cone. The lamps may be realized in form of bars or in radial form as retrofit in existing lamps.

The light is used to produce scenes in housing spaces in analogy to stage lighting. The atmosphere, the time of day and the location is identifiable by the light. The light fits to the scene and supports the general impression of the loca-tion. Different scenes are provided by the choice of modules.

By combining different modules, atmospheres may be created.

The modules may be adapted for lighting e.g. paintings and statues in museums.

Embodiments will now be described with reference to the ac-companying drawings.

Figure 1 illustrates a first embodiment of a lighting appa-ratus.

Figure 2 illustrates a second embodiment of a lighting appa-ratus.

Figure 3 illustrates a third embodiment of a lighting appa-ratus.

Figure 4 illustrates a fourth embodiment of a lighting appa-ratus.

Figure 5 illustrates a fifth embodiment of a lighting appa-ratus.

Figure 6 illustrates a sixth embodiment of a lighting appa-ratus.

Figure 7 illustrates a seventh embodiment of a lighting ap-paratus.

Figure 8 illustrates an eighth embodiment of a lighting ap-paratus.

Figure 9 shows a cross-section through a lighting apparatus.

Figure 10 illustrates the change of brightness during dim-ming.

Figure 11 illustrates spectrums of artificial and natural light.

Figure 12 illustrates spectrum of natural light.

Figure 13 illustrates spectrums of LED's.

Figure 1 shows a first embodiment of a lighting apparatus, illustrating a view on the lighting apparatus 1 being switched on. Eleven light-emitting diodes (LED's) 101 to 111 are arranged in a row. Each of the LED's 101 to 111 is fixed in a holder 2 and emits a light cone, which is indicated by a circle 3 around the holder 2. In the holder 2 of each LED, a character indicates the colour of the emitted light. The first LED 101, the sixth LED 106 and the last LED 111 emit orange light. The second LED 101 and the tenth LED 110 emit yellow light, whereas the third LED 103, the fifth LED 105, the seventh LED 107 and the ninth LED 109 emit red light each. The fourth LED 104 emits white light. The fourth LED 104 is a blue LED having a yellow covering such that the emitted light appears to be white. The LED 101 has one neighbour, as well as the LED 111, the other LED's have two neighbours.

The lighting apparatus emits a light that gives an impression of a sunrise. A light of a natural sunrise is mainly charac-terized by a wavelength that is close to orange. Thus, the orange LED's are placed at the outer positions of LED row.

Thus, an observer cannot differentiate between the colours of the inner LED's. He may not see the red light of LED 103, but a light being a mixture of the red colour with colours of the other LED's 102, 104, 106 and so on. The orange LED's 101 and 111 are placed at the outer positions because an observer would recognize that the colour of the outer LED is not close to the predominant colour.

The light of the LED row 1 is preferably reflected by walls and the ceiling of the room. The reflections ensure that the light of the LED's 101 to 111 is mixed several times.

The emulation of natural light is done by the following steps. The spectrum of the natural light is measured. The spectrum x(A) is the sum of all light intensities x at the respective wavelengths A. To emulate the natural spectrum, a spectrum is simulated by superimposing a plurality of LED's, the LED's being of dif-ferently coloured LED types. The superimposed spectrum is called predetermined spectrum.

The dominating impression of the colour of the predetermined spectrum is determined by an averaging step and is identified by measuring the spectral profile x(X) of the predetermined spectrum.

The spectral profiles of the LED's are measured. The LED of a first type has a intensity-wavelength function y1(2'), the LED of a second type has a intensity-wavelength function y2(A), the LED of a third type has a intensity-wavelength function y3(A).

Then correlation coefficients are calculated.

J x(2)yl(A)dA rhol= 0 x2(2)d2 * J y12(A)d2 x(2)y2(2)dA rho2= 0 Jx2(2)d2 *Jv22(2)d2 Jx(A)y3(A)dA rho3= 0 x2(2)d2 *J y32(2)d2 The LED basic module comprises coloured LED's arranged in form of a chain having an odd number of LED's. The outer po- sitions are at both ends of the chain. LED's having the larg-est correlation factor are positioned at the outer positions.

At the middle position of the chain preferably the same type of LED is positioned as at the outer positions.

For the inner positions, LED types with decreasing correla-tion factors are chosen. The other types of LED types are axis-symmetrically arranged between outer positions.

Figure 2 shows a second embodiment of the lighting apparatus in form of an LED row. The lighting apparatus 1 comprises eleven LED's 201 to 211. The first LED 201, the third LED 203, the sixth LED 206, the ninth LED 209 and the eleventh LED 211 emit blue light, while the second LED 202, the fourth LED 204, the eighth LED 208 and the tenth LED 210 emit green light. The fifth LED 205 emits yellow light and the seventh LED 207 emits red light.

The LED's having other colours than orange are placed at in-ner positions of the row 1. For a human observer, the light of the inner LED's is mixed with the light of the other LED' 5.

The lighting apparatus 1 emits the light of blue sky. The green and blue LED's are axis-symmetric in relation to a line perpendicular to the row in the middle of LED 206. The sky- light is mainly blue. Accordingly, the blue LED's are ar-ranged at the outer positions. The LED's 24 and 25, of which the wavelength is far away from blue, are arranged in the middle of the row.

Figure 3 shows a lighting apparatus according to a third em-bodiment. The first LED 301, the second LED 302, the fourth LED 304, the sixth LED 306, the eighth LED 308, the tenth 310 and eleventh LED 311 emit white light. The third LED 303 and the ninth LED 309 emit red light, while the fifth LED 305 emit yellow light and the seventh LED 307 emits green light.

This light emitted by this lighting apparatus 1 appears to be perfect white light. Again, the outer LED's emit white light, whereby LED's of other colours are placed at inner positions of the row.

Figure 4 illustrates a fourth embodiment of a lighting appa-ratus. The first LED 401, the third LED 403, the sixth LED 406, the ninth LED 409 and the eleventh LED 411 emit orange light. The second LED 402, the fourth LED 404, the eighth LED 408 and the tenth LED 48 emit white light. The fifth LED 405 and the seventh LED 407 emits green light.

The lighting apparatus according to the fourth embodiment emits light having a sand colour. Sand has a brown colour be-ing close to orange. Accordingly, the orange LED's are placed at the outer positions.

Figure 5 illustrates a fifth embodiment of a lighting appara-tus. The first LED 501, the sixth LED 506 and the eleventh LED 511 emit white light, while the second LED 502, the fourth LED 504, the eighth LED 508 and the tenth LED 510 emit yellow light. The third LED 503, the fifth LED 505, the sev-enth LED 507 and the ninth LED 509 emit green light. The light emitted by this lighting apparatus 1 appears to look like Caribbean water over sand.

Figure 6 illustrates a fifth embodiment of a lighting appara-tus. The first LED 601, the third LED 503, the fifth LED 505, the seventh LED 507, the ninth LED 509 and the eleventh LED 511 emit white light, while the second LED 502, the fourth LED 504, , the sixth LED 506, the eighth LED 508 and the tenth LED 510 emit green light. The light emitted by this lighting apparatus 1 appears to look like Caribbean water.

Figure 7 illustrates a seventh embodiment of a lighting appa-ratus. The first LED 701, the sixth LED 706 and the eleventh LED 711 emit white light, while the second LED 702, the fourth LED 704, the eighth LED 708 and the tenth LED 710 emit green light. The third LED 703, the fifth LED 705, the sev-enth LED 707 and the ninth LED 710 emit green light. The light emitted by this lighting apparatus 1 appears to look like dark blue sky.

Figure 8 illustrates an eighth embodiment of a lighting appa-ratus. The LED's of this lighting apparatus are arranged in circles around a white central LED 800. A first circle around the central LED 800 consists of six LED's 810, 811, 812, 813, 814 and 815. LED's with subsequent numbers are neighbours, whereby the LED's 810 and 815 are also neighboured. LED's 810, 812 and 814 are green, whereas LED's 811, 813 and 815 are red.

A second circle of LED 820, 821, 822, 823, 824, 825, 826, 827, 829, 8291 and 8292 is arranged around the first circle.

Again, LED's with subsequent numbers are neighboured, whereby LED's 829 and 8291 are neighboured as well as the LED's 8292 and 820. The LED's 820, 824 and 828 emit green light, whereas the LED's 821, 823, 825, 827, 829 and 8292 emit yellow light.

The LED's 822, 826 and 8291 emit red light.

A third circle, which is the outer circle of the lighting ap-paratus 1 is arranged surrounding the second circle. The third circle comprises the LED's 830, 831, 832, 833, 834, 835, 836, 837, 838, 839, 840, 841, 842, 843, 844, 845, 846 and 847 which all emit white light. The lighting apparatus 1 emits a perfect white light. Thus, the white LED's are ar-ranged in the outer positions of this apparatus.

The outer positions are those of the LED's 830, 845, 842, 839, 836 and 833 because they have the largest distance to the centre of the lighting apparatus which is the centre of LED 800.

The white LED is the predominant colour of the overall spec-trum of the lighting apparatus. Accordingly, white LED's are placed at the outer positions and in the centre. As it will be seen in Figure 11, natural white light also comprises lar-ger intensities of red and green light.

Figure 9 shows a cross-section through a lighting apparatus.

There are shown two LED's having a distance d, which is 10 mm in this embodiment. The distance is measured from the centre of the light-emitting part of the first LED 101 to the centre of the light-emitting part of the second LED 102. The LED's are placed in holders 1001 and 1002 that form an opening each. The holders 1001 and 1002 are covered by a reflecting metal to reflect the light from the LED's. The light emitted by the LED's leaves the holder 1001 and 1002 through the opening, whereby the angle of the light cone depends on the characteristics of the LED's and the position of the open-ings. The upper ends of the holders are a length f above the upper end of the LED's. The length f is 1 mm in this case.

Figure 10 illustrates characteristics of 3 LED's having dif-ferent colours. The colour generated by a string comprising these three LED's may vary with the brightness. In a first embodiment, this is achieved by equalling the current through all LED's, independent of the brightness. The brightness L is drawn in dependence of the current through the LED's. The left LED is orange, the LED in the middle is yellow and the right LED is red. For all LEDs, the brightness of the emit-ted light increases along with increasing current. However, the degree of increase differs. At a first predetermined cur-rent Ii, the brightness of the orange LED is higher than the brightness of the red LED, which is brighter than the yellow LED. Accorthngly, a current Ii f1owng through a string of these LED's gives an impression of a mainly red colour.

However, at a second current 12 that is higher than Ii, the lightness of the orange LED is higher than the lightness of the yellow LED. The lightness of the yellow LED is larger than the lightness of the red LED. Accordingly, the light emitted by a string of these three LED's gives a main impres-sion of yellow.

Figure 11 shows five examples for spectrums of white light, the spectrum being represented by the relative intensity in dependency of the wavelength. The examples are a white colour that looks cool, a light from a Sylvania Gro-Lux'TM lamp, a colour generated by a tungsten filament, a natural white col-our and the light of a low-pressure sodium lamp. All the spectrums of artificial light differ from the natural white significantly. Especially the wavelengths of green light around 550 nm are missing in the artificial light.

Figure 12 shows further spectrums of natural light. The exam-ples are, on the left hand side, a north sky light, a noon daylight, a noon sunlight, and a combination of a sunset sky and a sunlight. One the right hand side, spectrums of a blue sky and a red sunset are shown.

Figure 13 shows the spectrums of seven types of LED's. By combining LED's of different types as described above, the intensities of these LED's interpose to generated a spectrum that is close to one of the spectrums of natural light.

Claims

Claims 1. Lighting apparatus (1) for lighting a room with a light having a predetermined spectrum of wavelengths, the lighting apparatus (1) -having a plurality of light-emitting diodes (101 to 111), -and having a housing (1000) with a plurality of outer and inner positions, in which the light-emitting diodes are placed, whereby a first subset of the plurality of light-emitting diodes (101, 111) emits light of a first colour (0) and a second subset (103,105,109) of the plurality of light-emitting diodes emits light of a second col-our(R) , the spectrum of the first colour (0) being closer to the spectrum of the predetermined spectrum than the spectrum of the second colour(R) to the prede-termined spectrum, whereby the light-emitting diodes (101, 111) of the first subset are placed at the outer positions of the apparatus and the light-emitting diodes of the second subset are placed at inner positions of the apparatus.
2. Lighting apparatus according to claim 1, whereby the arrangement of the colours of the light emitting diodes (101 to 111) is axis-symmetrical.
3. Lighting apparatus according to claim 1 or 2, whereby the central LED has the same colour as the outer ones.
4. Lighting apparatus according to claim 1, 2 or 3, whereby the number of light-emitting diodes is odd.
5. Lighting apparatus according to one of the claims 1 to 4' whereby the positions (101, 111) form a row.
6. Lighting apparatus according to one of the claims 1 to 5' whereby the positions are placed concentrically.
7. Lighting apparatus according to one of the claims 1 to 6, whereby for the distance d between neighboured light-emitting diodes, the following condition holds: 5mm < d < 30 mm.
8. Lighting apparatus according to claim 7, whereby the light cone of each of the light-emitting di-odes has an opening angle of 160 and 170 degree.
9. Lighting apparatus according to claim 8, whereby each LED is placed in a holder whereby upper part of the light-emitting diode is 0 mm to 1mm lower than opening end of the holder. This ensures that the light cones are completely mixed.
10. Lighting apparatus according to one of the claims 1 to 9, whereby the plurality of LED's consists of 11 to 21 LED' 5.
11. Lighting apparatus according to one of the claims 1 to 10, whereby the distance between two spectrums are de-fined by the correlation factors of the spectrums.
12. Lighting apparatus substantially as described herein with reference to, and as illustrated in, the accompany-ing drawings.
13. Method to emulate of natural light, the method compris-ing the following steps: -measurement of the spectrum of natural light, -superimposing a plurality of LED's, the LED's being of differently coloured LED types, -calculating the correlation factors between the spec-trum of the natural light and LED types, -positioning the LED having the largest correlation factor at the outer position of the LED's in a housing.