背景技术：
[0002] Through the years, there has been a demand for altering the light source color (correlated color temperature) of room illumination at households and workplaces, in accordance with the season, the time of day, and the occasion. Regarding the seasons, for example, a cool color such as whitish light may be suitable for summer seasons, whereas a warm color such as reddish light may be suitable for winter seasons. Regarding the time of day, a daylight color may be suitable during work hours because the color is said to help improving the work efficiency. During a break, on the other hand, an incandescent lamp color may be suitable because the color is relaxing.
[0003] Considering the purpose of room illumination, it is desirable to vary the light source color while maintaining a natural appearance as much as possible. In other words, it is desirable that the light source color vary so as to precisely or generally trace the Planckian Locus on the 1931 CIE chromaticity diagram.
[0004] Conventionally, the majority of room illumination sources are fluorescent lamps. Unfortunately, however, the light source colors of fluorescent lamps are fixedly determined depending on the mixing ratio of different phosphors. Thus, in order to change the light source color of a fluorescent lamp currently used for room illumination, the fluorescent lamp itself needs to be replaced with a fluorescent lamp having a desired light source color each time such a change is requested, which is too much trouble.
[0005] In view of the above, attention is being given to LEDs, which are now available in all three primary colors of red, green, and blue, thanks to recently introduced high-efficiency blue LEDs. A light source composed of a plurality of red, green, and blue LEDs arranged close to one another will produce light of a desired color as a result of mixture of red, green, and blue light (see, for example, JP Patent Application Publication No. 2004-6253). On the 1931 CIE chromaticity diagram, the light source colors of red, green, and blue LEDs are represented by apexes of a triangle encompassing the Planckian Locus. Consequently, by adjusting the relative light intensities of LEDs of the respective colors (a power supply to each LED), the light source color can be varied so as to precisely or generally follow the Planckian Locus. That is to say, a single light source can generate light of a variable color while maintaining the light close to natural light.
[0006] However, with the use of red, green, and blue LEDs, it is required to delicately control the proportions of three colors, i.e. the proportions of power supplies to the LEDs. In order to perform such delicate control, a costly control system is required.
[0007] In view of the above problems, the present invention aims to provide an illumination source of which light source color is variable in a state close to natural light, with easier control than conventionally required.
具体实施方式：
[0044] Hereinafter, a description is given to illumination sources according to embodiments of the present invention, with reference to the accompanying drawings.
[0045] Prior to a specific description of illumination sources according to the embodiments, the principles of the present invention will be described with reference to FIG. 1. FIG. 1A is the 1931 CIE chromaticity diagram (hereinafter, this specific 1931 CIE chromaticity diagram is simply referred to as the “chromaticity diagram”).
[0046] An illumination source according to the present invention basically has a first light source and a second light source. On the chromaticity diagram, the color of the first light source is represented by a first point P1, whereas the color of the second light source is represented by a second point P2. By causing the first light source to solely emit light, the first light source color is obtained. By causing both the first and second light sources to emit light at the same time, a mixture of the first and second light source colors is produced.
[0047] The first point P1 is substantially on the Planckian Locus PL. The wording “substantially on” means that the first point P1 is located, on the CIE 1960uv chromaticity diagram, within a range of −5≦duv≦10, where duv (chromaticity deviation) is a result obtainedby multiplying a distance from the Planckian Locus by 1000. (Note that duv takes on a positive value when the first point P1 is above the Planckian Locus along the Y axis, and a negative value when the first point P1 is below the Planckian Locus.) The above range of −5≦duv≦10 substantially coincides with a range of deviation, from the Planckian Locus, of the chromaticity regions of five typical light source colors (daylight, daylight white, white, warm white, and incandescent lamp colors) of fluorescent lamps defined in Japanese Industrial Standard (JIS): Z9112. That is, one principal application of the illumination source of the present invention is to be used as a replacement for a fluorescent lamp. Note that five quadrilaterals in FIG. 1A represent the chromaticity regions of the five colors defined in JIS mentioned above, namely daylight D, daylight white W, white W, warm white WW, and incandescent lamp color L. The correlated color temperatures of the five light source colors fall within a range of the lowest of 2600 K to the highest of 7100 K. The illumination source of the present application is designed to have a light source color of which correlated color temperature varies within the above-specified range.
[0048] Next, the position of the second point P2 is described by additionally referencing to FIG. 1B. FIG. 1B is an enlarged view of the first point P1 and its nearby area. The second point P2 resides at such a position that a line segment L1 connecting the points P1 and P2 is substantially in parallel with a line L3 tangent to the Planckian Locus PL at a point on a line L2. The line L2 is normal to the Planckian Locus PL and passes through the first point P1.
[0049] Here, a description is given to the meaning of “the line segment L1 is substantially in parallel with the tangent line L3”. The first light source color corresponds to the first point P1, whereas the second light source color corresponds to the second point P2. Combination of the first and second light source colors results in the creation of a color (determined depending on the proportions of the two colors) represented by the coordinates locating a point (point P1•2) on the line segment L1 connecting the chromaticity coordinates of the two colors. In the following embodiments, the first light source is always made to emit light, whereas the second light source is made to emit light at a varying intensity (relative intensity) so as to obtain a desired light source color (color temperature). In order to keep the point P1•2 within the range of −5≦duv≦10 as much as possible, the line segment L1 is required to extend along the Planckian Locus PL. The wording “the line segment L1 is substantially in parallel with the tangent line L3” means that the line segment L1 is made to extend along the tangent line L3 so that the point P1•2 falls in the range of −5≦duv≦10. In other words, it is sufficient that the line segment L1 is in parallel with the tangent line L3 (i.e. the line segment L1 and the tangent line L3 extend in a substantially same direction) to an extent that the point P1•2 falls in the range of −5≦duv≦10 as the light intensity of the second light source is made to vary relative to the first light source. The wording “substantially in parallel” is used to express the above meaning.
[0050] Furthermore, the wording “substantially in parallel” includes cases where the line segment L1 intersects the Planckian Locus PL. Specifically, the wording include cases where (i) the first point P1 is on the Planckian Locus PL and the line segment L1 intersects the Planckian Locus PL once, (ii) the first point P1 is inside the Planckian Locus PL that smoothly curves and the line segment L1 intersects the Planckian Locus PL once, (iii) the first point P1 is outside the Planckian Locus PL that smoothly curves and the line segment L1 intersects the Planckian Locus PL twice, and (iv) the first point P1 is outside the Planckian Locus PL that smoothly curves and the line segment L1 is tangent to the Planckian Locus PL.
[0051]FIGS. 2 and 3 are graphs showing, regarding each of illumination sources of later-described specific examples, the light source color (correlated color temperature Tc and chromaticity deviation duv) plotted against the general color rendering index Ra, as the light intensity of the second light source is varied relatively to the first light source. Numbers in parentheses correspond to the examples. References will be made to FIGS. 2 and 3 as necessary in a description of each example.
EMBODIMENT 1
[0052]FIG. 4A is a plan view and FIG. 4B is a front view both showing the schematic structure of an illumination source 2 according to an embodiment 1.
[0053] The illumination source 2 is composed of a multi-layer printed wiring board 4 (hereinafter, simply “printed wiring board 4”) and light emitting elements which are white LEDs 6 and orange LEDs 8 mounted on the printed wiring board 4. Specifically, twelve white LEDs 6 and seven orange LEDs 8 are mounted. Each of the LEDs 6 and 8 is so-called a bullet-shaped LED. The white LEDs 6 and the orange LEDs 8 are electrically connected by the wiring (not illustrated) of the printed wiring board 4, as shown in a circuit diagram of FIG. 4C. More specifically, the twelve white LEDs 6 are serially connected (the serially connected twelve white LEDs 6 are correctively referred to as a “white LED array 10”) and the seven orange LEDs 8 are serially connected (the serially connected seven orange LEDs 8 are collectively referred to as an “orange LED array 12”). In the embodiment 1, the first light source is constituted by the white LED array 10, whereas the second light source is constituted by the orange LED array 12.
[0054] The anode of a white LED 6A which is positioned at the high-potential end of the white LED array 10 is connected to a power supply terminal 16 across a limited resistance 14 (not shown in FIG. 4A) mounted on the printed wiring board 4. The anode of an orange LED 8A which is positioned at the high-potential end of the orange LED array 12 is connected to a power supply terminal 20 across a limited resistance 18 (not shown in FIG. 4A) mounted on the printed wiring board 4. In addition, the cathode of a white LED 6B and the cathode of an orange LED 8B are both connected to a common terminal 22 by the wiring (not illustrated) of the printed wiring board 4. The white LED 6B and the orange LED 8B are positioned at the low-potential ends of the respective LED arrays 10 and 12.
[0055] The illumination source 2 having the above structure is driven by a variable power device 24 known in the art. Specifically, the variable power device 24 has variable power units 24A and 24B for controlling the power supply to the power supply terminals 16 and 20, respectively. By separately controlling the power supply to the respective power supply terminals, only one of the LED arrays may be made to illuminate or both the LED arrays may be made to illuminate at the same time. Furthermore, when both the LED arrays are made to concurrently illuminate, the relative light intensities of the LED arrays may be adjusted. As shown in FIG. 4A, the white LEDs 6 and the orange LEDs 8 are arranged close to one another in a well-balanced pattern. Thus, the illumination source 2 emits light in a light source color created as a result of sufficiently mixing the white light from the white LEDs 6 and the orange light from the orange LEDs 8. Preferably, the drive current for LEDs is controlled by pulse-width modulation (PWM). That is, the variable power device 24 is preferably controllable by PWM. With the PWM control, wavelength shifts are prevented from occurring when the power supply is varied.
[0056] As later described, each white LED 6 is composed of predetermined phosphors packaged with a blue LED chip emitting blue light or with a near-ultraviolet (NUV) LED chip emitting near-ultraviolet light. The white LED 6 emits white light created as a combination of a color of light emitted directly by the chip and a color of light converted by the phosphors. On the other hand, each orange LED 8 is composed of a packaged orange LED chip, and emits orange light as directly emitted by the orange LED chip. In the present embodiment, a GaInN-based LED is used as the blue LED chip and NUV LED chip mentioned above, whereas an AlGaInP-based LED is used as the orange LED chip mentioned above.
[0057] Regarding the white LEDs 6, used in combination with a blue LED chip are green and red phosphors that convert blue light to green and red light, respectively. The phosphor of each color used in this embodiment is expressed by the following chemical formula. Green Phosphor(Sr, Ba, Ca)2SiO4: Eu2+Hereinafter, ssimnply “Green SSY”Red PhosphorSr2Si5N8: Eu2+Hereinafter, simply “Red NS”
[0058] In addition, used in combination with an NUV LED chip are blue, green, yellow, and red phosphors that convert near-ultraviolet light to blue, green, yellow, and red light, respectively. The phosphor of each color used in this embodiment is expressed by the following chemical formula. Green PhosphorBaMgAl10O17: Eu2+, Mn2+Hereinafter, simply “Green BTM”Red PhosphorSr2Si5N8: Eu2+Hereinafter, simply “Red NS”Blue Phosphor(Ba, Sr)2MgAl10O17: Eu2+Hereinafter, simply “Blue BAT”Yellow Phosphor(Sr, Ba, Ca)2SiO4: Eu2+Hereinafter, simply “Yellow SSY”
[0059] Now, a description is given to specific examples which fall within the scope of the embodiment 1.
EXAMPLE 1
[0060]FIG. 5 is a diagram showing the spectral distributions of light emitted by the blue LED chip, the green phosphor (Green SSY), the red phosphor (Red NS), and the orange LED chip all used in an example 1. In FIG. 5, the spectral outputs are all plotted to uniformly reach a peak of the value “1”. As shown in FIG. 5, the blue LED chip used in this example has a peak emission wavelength at 460 nm and the orange LED chip has a peak emission wavelength at 585 nm. The spectral distributions of the respective colors of light emitted by the green phosphor (Green SSY) and the red phosphor (Red NS) are as shown in FIG. 5.
[0061] In the case where the illumination source 2 of the example 1 is made to illuminate solely by the white LED array 10 (FIG. 4), the relative intensities of the blue light (blue LED chip), the green light (green phosphor), and the red light (red phosphor) are as shown in FIG. 6A (in the drawings, the word “phosphor” may be abbreviated as “phos”). The resultant white light exhibits the correlated color temperature Tc of 6872 K (chromaticity deviation duv=1.2) and the general color rendering index Ra of 91. Note that the relative intensities are the ratios of the peak wavelength values of the respective color components of the white light. The x and y coordinates specified in the figure locate the light source color on the chromaticity diagram (1931 CIE chromaticity diagram), and the u and v coordinates locate the light source color on the CIE 1960uv chromaticity diagram (not illustrated).
[0062] On the chromaticity diagram shown in the figure, an open circle “◯” is at the position representing the light source color produced solely by the white LED array 10 (FIG. 4), which constitutes the first light source. Thus, the open circle “◯” coincides with the first point P1 mentioned above.
[0063] On the chromaticity diagram in the figure, a black circle “●” is shown at the position representing the light source color that would be produced given that the orange LED array 12 (FIG. 4), which constitutes the second light source, is made to illuminate. Thus, the black circle “●” coincides with the second point P2 mentioned above.
[0064] In the case where both the white LED array 10 and the orange LED 12 are made to illuminate at the same time, the relative intensities of the blue light (blue LED chip), the green light (green phosphor), the orange light (orange LED), and the red light (red phosphor) are as shown in FIG. 6B. The resultant white light exhibits the correlated color temperature Tc of 4185 K (chromaticity deviation duv=1.0) and the general color rendering index Ra of 51. On the chromaticity diagram in the figure, an open square “⋄” is shown at the position representing the color of the white light on the chromaticity diagram. The illumination source 2 on the whole emits light in a light source color represented by the coordinates of the open square “⋄” (hereinafter, the light source color produced by causing both the white LED array 10 and the orange LED array 12 to concurrently illuminate is referred to as a “mixture color”).
[0065] It is naturally appreciated that the mixture color may be arbitrarily varied within a wide range as indicated by the line (1) in FIG. 2, by adjusting the relative light intensity of the orange LED array 12 to the white LED array 10. When the correlated color temperature Tc is within the range of 6872≧Tc≧3100, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 5600≦Tc≦6872, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 6650≦Tc≦6872, the general color rendering index Ra is not less than 90.
[0066] In the chromaticity diagrams which will be referred to in a description of each example, the open circle “◯” indicates the position representing the light source color produced solely by the first light source (white LED array). The black circle “●” indicates the position representing the light source color that would be produced if the second light source (orange LED array) is made to solely illuminate. The open square “⋄” indicates the position representing the light source color produced by causing both the first and second light sources to illuminate at the same time.
EXAMPLE 2
[0067] An example 2 is basically identical to the example 1, except that each white LED is composed of an NUV LED chip instead of a blue LED chip.
[0068]FIG. 7 is a diagram showing the spectral distributions of light emitted by the NUV LED chip, the green phosphor (Green BTM), the red phosphor (RED NS), the blue phosphor (Blue BAT), the yellow phosphor (Yellow SSY), and the orange LED chip all used in the example 2. In FIG. 7, similarly to FIG. 5, the spectral outputs are all plotted to uniformly reach a peak of the value “1”. As shown in FIG. 7, the NUV LED chip has a peak emission wavelength at 395 nm, whereas the orange LED chip has a peak emission wavelength at 585 nm, similarly to the one used in the first example. The spectral distributions of the respective colors of light emitted by the green phosphor (Green BTM), the red phosphor (Red NS), the blue phosphor (Blue BAT), and the yellow phosphor (Yellow SSY) are as shown in FIG. 7.
[0069] In the case where the illumination source 2 of the example 2 is made to illuminate solely by the white LED array 10 (FIG. 4), the relative intensities of the blue light (blue phosphor), the green light (green phosphor), the yellow light (yellow phosphor), the yellow light (yellow phosphor), the red light (red phosphor), and the near-ultraviolet light (NUV LED chip) are as shown in FIG. 8A. The resultant white light exhibits the correlated color temperature Tc of 7017 K (chromaticity deviation duv=0.7) and the general color rendering index Ra of 91.
[0070] In the case where both the white LED array 10 and the orange LED array 12 are made to illuminate at the same time, the relative intensities of the blue light (blue LED chip), the green light (green phosphor), the red light (red phosphor), the near-ultraviolet light (NUV LED chip), and the orange light (orange LED) are as shown in FIG. 8B. The resultant white light exhibits the correlated color temperature Tc of 5291 K (chromaticity deviation duv=−0.9) and the general color rendering index Ra of 80.
[0071] Similarly to the example 1, it is naturally appreciated that the mixture color may be arbitrarily varied within a wide range as indicated by the line (2) in FIG. 3, by adjusting the relative light intensity of the orange LED array 12 to the white LED array 10. When the correlated color temperature Tc is within the range of 7107≧Tc≧3070, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 5280≦Tc≦7017, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 5950≦Tc≦7017, the general color rendering index Ra is not less than 90.
[0072] As described above, the illumination source 2 according to embodiment 1 undergoes changes in light source color (correlated color temperature) by controlling power supplies to the white LED array 10 and the orange LED array 12 (by controlling two power supply systems). The control required herein is easier than conventional control of power supplies to LEDs of R, G, and B (control of three power supply systems). Furthermore, the correlated color temperature is variable within the above-mentioned range and the color deviation is maintained within the above-mentioned range.
EMBODIMENT 2
[0073] An embodiment 2 of the present invention is basically similar to the embodiment 1, and the different lies mainly in the structure of the second light source (orange LED array) Accordingly, the same reference numerals are used to denote the same components, and no or brief description is given to such components. A description hereinafter focuses on the difference.
[0074] In the embodiment 1, the second light source is composed of the orange LEDs 8 (FIG. 4) all of which are of the same type. In the embodiment 2, the second light source is composed of two types of orange LEDs. The difference between the two types of orange LED lies in peak emission wavelength.
[0075]FIG. 9A is a plan view and FIG. 9B is a front view both showing the schematic structure of an illumination source 32 according to the embodiment 2.
[0076] The illumination source 32 is composed of a multi-layer printed wiring board 34 (hereinafter, simply “printed wiring board 34”), and a plurality of bullet-shaped LEDs mounted on the printed wiring board 34 in the same pattern as the embodiment 1.
[0077] Among the LEDs, six LEDs denoted by the reference numeral 36 are orange LEDs having a first peak emission wavelength and four denoted by the reference numeral 38 are orange LEDs having a second peak emission wavelength shorter than the first wavelength. Specific examples of the first and second wavelengths will be mentioned later in descriptions of examples. Note that the white LEDs 6 are identical to those used in the embodiment 1, although a smaller number of them are used in this embodiment.
[0078] The white LEDs 6 and the orange LEDs 36 and 38 are electrically connected by the wiring (not illustrated) of the printed wiring board 34, as shown in a circuit diagram of FIG. 9C. Specifically, nine white LEDs 6 are serially connected (hereinafter, the nine serially connected white LEDs 6 are collectively referred to as a “white LED array 40”). Furthermore, the six orange LEDs 36 are serially connected to constitute a first LED array 42, and the four orange LEDs 38 are serially connected to constitute a second LED array 44. The LED arrays 42 and 44 are connected in parallel across limited resistances 46 and 48 (hereinafter, the parallel connected LED arrays 42 and 44 are collectively referred to as an “orange LED array 50”). In the embodiment 2, the first light source is constituted by the white LED array 40 and the second light source is constituted by the orange LED array 50.
[0079] The resistivity ratio between the limited resistances 46 and 48 is set so as to make the first and second LED arrays 42 and 44 substantially equal to each other in light intensity (peak wavelength value). With this arrangement, the orange LED array 50 produces a light source color represented on the chromaticity diagram substantially by a midpoint between the chromaticity coordinates of the first LED array 42 and of the second LED array 44.
[0080] Hereinafter, a description is given to specific examples 3-13 which fall within the scope to the embodiment 2. Note that the white LEDs 6 used in the examples 3-8 are composed of blue LED chips, whereas the white LEDs 6 used in the examples 9-13 are composed of NUV LED chips.
EXAMPLE 3
[0081]FIG. 10 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 3. The wavelength peaking at 625 nm is a wavelength component of the first LED array 42 (FIG. 9), and the wavelength peaking at 565 nm is a wavelength component of the second LED array 44 (FIG. 9).
[0082]FIG. 11A is a diagram showing the spectral distribution of light emitted solely by the white LED array 40 (FIG. 9). FIG. 11B shows the coordinates of the light source color on the chromaticity diagram, along with other data. The resultant white light exhibits the correlated color temperature Tc of 7112 K (color deviation duv=0.3) and the general color rendering index Ra of 91.
[0083]FIG. 12A is a diagram showing the spectral distribution of light emitted by causing both the white LED array 40 and the orange LED array 50 to illuminate at the same time. FIG. 12B shows the coordinates of the light source color on the chromaticity diagram, along with other data. The resultant white light exhibits the correlated color temperature Tc of 4071 K (color deviation duv=0.9) and the general color rendering index Ra of 85.
[0084] The mixture color may be arbitrarily varied within a wide range as indicated by the line (3) in FIG. 2, by adjusting the relative light intensity of the orange LED array 50 to the white LED array 40. When the correlated color temperature Tc is within the range of 7112≧Tc≧3110, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc falls within the range of 3650≦Tc≦7112, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 4860≦Tc≦7112, the general color rendering index Ra is not less than 90.
EXAMPLE 4
[0085]FIG. 13 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 4. The wavelength peaking at 620 nm is a wavelength component of the first LED array 42 (FIG. 9), and the wavelength peaking at 570 nm is a wavelength component of the second LED array 44 (FIG. 9).
[0086]FIG. 14A shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced solely by the white LED array 40 (FIG. 9). The resultant white light exhibits the correlated color temperature Tc of 7112 K (color deviation duv=0.3) and the general color rendering index Ra of 91.
[0087]FIG. 14B shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced by causing both the white LED array 40 and the orange LED array 50 to illuminate at the same time. The resultant white light exhibits the correlated color temperature Tc of 4234 K (color deviation duv=−4.5) and the general color rendering index Ra of 83.
[0088] Furthermore, the mixture color may be arbitrarily varied within a wide range as indicated by the line (4) in FIG. 2, by adjusting the relative light intensity of the orange LED array 50 to the white LED array 40. When the correlated color temperature Tc is within the range of 7112≧Tc≧2550, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 3870≦Tc≦7112, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 5450≦Tc≦7112, the general color rendering index Ra is not less than 90.
EXAMPLE 5
[0089]FIG. 15 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 3. The wavelength peaking at 615 nm is a wavelength component of the first LED array 42 (FIG. 9), and the wavelength peaking at 575 nm is a wavelength component of the second LED array 44 (FIG. 9).
[0090]FIG. 16A shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced solely by the white LED array 40 (FIG. 9). The resultant white light exhibits the correlated color temperature Tc of 6950 K (color deviation duv=4.5) and the general color rendering index Ra of 91.
[0091]FIG. 16B shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced by causing both the white LED array 40 and the orange LED array 50 to illuminate at the same time. The resultant white light exhibits the correlated color temperature Tc of 4451 K (color deviation duv=−4.2) and the general color rendering index Ra of 81.
[0092] Furthermore, the mixture color may be arbitrarily varied within a wide range as indicated by the line (5) in FIG. 2, by adjusting the relative light intensity of the orange LED array 50 to the white LED array 40. When the correlated color temperature Tc is within the range of 6950≧Tc≧4020, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 4500≦Tc≦6950, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 6300≦Tc≦6950, the general color rendering index Ra is not less than 90.
EXAMPLE 6
[0093] In the examples 3-5 above, the resistivity ratio between the limited resistances 46 and 48 is set so as to make the first and second LED arrays 42 and 44 shown in FIG. 9 substantially equal in light intensity (peak wavelength value).
[0094] In the example 6 and later-described examples 7 and 8, on the other hand, the resistivity ratio between the limited resistances 46 and 48 is set so as to make the first LED array 42 greater in light intensity (peak wavelength value) than the second LED array 44 (the first and second LED arrays 42 and 44 are shown in FIG. 9). With this arrangement, the position (second point) on the chromaticity diagram representing the light source color of the orange LED array 50 shifts toward longer wavelengths along the spectrum locus of monochromatic light around 560-620 nm. Thus, according to the examples 6-8, the mixture color is variable within a range of lower color temperatures than the range variable in the examples 3-5.
[0095] Note that the above arrangements to set the first and second LED arrays 42 and 44 to mutually different light intensities are exemplary and not limiting. Instead, for example, an arrangement as shown in FIG. 9D may be made. Specifically, the first and second LED arrays 42 and 44 are serially connected. In this case, the intensity ratio of the first and second LED arrays 42 and 44 is determined by the ratio of the numbers of LEDs constituting the respective LED arrays.
[0096]FIG. 17 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 6. The wavelength peaking at 625 nm is a wavelength component of the first LED array 42 (FIG. 9), and the wavelength peaking at 565 nm is a wavelength component of the second LED array 44 (FIG. 9).
[0097]FIG. 18A is a diagram showing the spectral distribution of light emitted solely by the white LED array 40 (FIG. 9). FIG. 18B shows the coordinates of the light source color on the chromaticity diagram, along with other data. The resultant white light exhibits the correlated color temperature Tc of 4402 K (color deviation duv=−0.5) and the general color rendering index Ra of 94.
[0098]FIG. 19A is a diagram showing the spectral distribution of light emitted by causing both the white LED array 40 and the orange LED array 50 to illuminate at the same time. FIG. 19B shows the coordinates of the light source color on the chromaticity diagram, along with other data. The resultant white light exhibits the correlated color temperature Tc of 2938 K (color deviation duv=0.2) and the general color rendering index Ra of 89.
[0099] The mixture color may be arbitrarily varied within a wide range as indicated by the line (6) in FIG. 2, by adjusting the relative light intensity of the orange LED array 50 to the white LED array 40. Suppose, for example, the mixture color is varied so that the correlated color temperature Tc of 4402 sifts lower. In this case, when the correlated color temperature Tc is 2600 K, the value of duv is 3.7. When the correlated color temperature Tc is within this range, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 2500≦Tc≦4402, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 3030≦Tc≦4402, the general color rendering index Ra is not less than 90.
EXAMPLE 7
[0100]FIG. 20 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 7. The wavelength peaking at 620 nm is a wavelength component of the first LED array 42 (FIG. 9), and the wavelength peaking at 570 nm is a wavelength component of the second LED array 44 (FIG. 9).
[0101]FIG. 21A shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced solely by the white LED array 40 (FIG. 9). The resultant white light exhibits the correlated color temperature Tc of 4402 K (color deviation duv=−0.5) and the general color rendering index Ra of 94.
[0102]FIG. 21B shows, along with other data, the coordinates locating on the chromaticity diagram the light source color produced by causing both the white LED array 40 and the orange LED array 50 to illuminate at the same time. The resultant white light exhibits the correlated color temperature Tc of 3020 K (color deviation duv=−5.0) and the general color rendering index Ra of 87.
[0103] The mixture color may be arbitrarily varied within a wide range as indicated by the line (7) in FIG. 2, by adjusting the relative light intensity of the orange LED array 50 to the white LED array 40. Suppose, for example, the mixture color is varied so that the correlated color temperature Tc of 4402 sifts lower. In this case, when the correlated color temperature Tc is 2600 K, the value of duv is −3.6. When the correlated color temperature Tc is within this range, the value of duv is maintained within the range of −5≦duv≦10. In addition, when the correlated color temperature Tc is within the range of 2600≦Tc≦4402, the general color rendering index Ra is not less than 80. When the correlated color temperature Tc is within the range of 3290≦Tc≦4402, the general color rendering index Ra is not less than 90.
EXAMPLE 8
[0104]FIG. 22 is a diagram showing the spectral distribution of light emitted by the orange LED array 50 (FIG. 9) used in the example 8. The wavelength peaking at 615 nm is a wavelength component of the first LED array 42