Patent Application
20150019168
The present invention relates to an LED classification method for classifying a plurality of LEDs (light-emitting diodes) on the basis of their chromaticity distribution as to whether or not they can be used in a backlight of a liquid crystal display apparatus.
In recent years, as backlights of liquid crystal display apparatuses, backlights using long-lived and micropower LEDs as light sources are becoming widely used. Such a backlight normally uses white LEDs. A white LED is generally constituted by a combination of a blue LED and a phosphor. Such a white LED gives a white light through a color mixture of (a) a blue light emitted from the blue LED chip and (b) light emitted by the phosphor's being excited by the blue light. For example, a white LED using a green and a red phosphors gives a white light through a color mixture of (a) a green and being excited by a blue light and (b) the blue light.
In order for such a white LED to be used in a backlight, it is necessary to apply a phosphor according to the display characteristics of a liquid crystal panel in a liquid crystal display apparatus so that the white LED emits a desired color of white.
For example, Patent Literature 1 discloses a method that makes it possible to easily and quickly provide to a manufacturing process a phosphor capable of converting a luminescent color of white produced by a blue LED and a phosphor into a more even tone of color. In this method, with respect to a content correlated with a relationship between light source color information and required luminescent color information of a white LED through a coefficient associated with a phosphor material, a phosphor material associated with a coefficient found by applying light source color information and required luminescent color information of a particular white LED as presented by a client is specified. This makes it possible to, without the need to wait for a light-emitting element to be actually obtained, quickly obtain, as phosphor-specifying information, the type of a phosphor raw material, the composition ratio of thereof, the mixing ratio (part(s) by weight) thereof with respect to the base material, etc. that substantially satisfy the requested luminescent color information as requested by the client.
Meanwhile, Patent Literature 2 discloses a method in which a white LED can be quickly manufactured by calculating such a mixing concentration of a phosphor by software in a non-trial-and-error manner that the white LED has high color reproducibility. In this method, first, a process of causing a mixed-lighting spectrum and a standard spectrum to approximate to each other is performed, the mixed-lighting spectrum having been obtained through a mixture of (a) light from two types of phosphor whose concentrations have been adjusted and (b) light from an LED. Next, a process of calculating the amount of space that is surrounded by the chromaticity coordinates of the three primary colors into which the mixed-lighting spectrum has been divided by a color filter and calculating the chromaticity coordinate position of a white light constituted by the three primary colors. Such a process is computationally executed.
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2001-107036 A (Publication Date: Apr. 17, 2001)
Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2010-93237 A (Publication Date: Apr. 22, 2010)
Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2007-322850 A (Publication Date: Dec. 13, 2007)
Each of these methods disclosed in Patent Literatures 1 and 2 is a method in which the concentration etc. of a phosphor during the manufacture of a white LED is determined. However, in the case of a backlight using a plurality of white LEDs each constituted by a combination of a blue LED and a phosphor, forming a phosphor layer so that the phosphor is used in a desired concentration and amount is very difficult even with such an optimum determination of the concentration etc. of the phosphor. For this reason, there is nonuniformity in the concentration and amount of the phosphor during the manufacture among the white LEDs. Further, since there are also variations in the characteristics of the blue LEDs and the light-emitting layers among products, there are variations in the peak wavelength of blue lights among the white LEDs. This causes variations in the balance of light intensity between the excitation lights of the phosphors and the blue lights of the blue LEDs, so there is also undesirably variation in chromaticity among the white LEDs.
Direct use of such chromaticity-varied white LEDs in a backlight presents such inconvenience that there is nonuniformity in display colors within a display surface. Conventionally, such inconvenience has been overcome by selecting, for use in a backlight, only white LEDs so classified according to chromaticity rank that their chromaticity distribution falls within a predetermined range.
However, even as a result of selecting white LEDs that emit lights whose chromaticity falls within a predetermined range, the chromaticity of the white LEDs on a panel display after transmission of the lights through the liquid crystal panel is divided by the influence of the color filter in particular into groups falling within a range of variation in chromaticity according to the peak wavelengths of the blue lights, with the result that there is an enlargement in the range of variation. This leads to the emergence of white LEDs that deviate from the desired chromaticity rank range on the panel display of the liquid crystal panel. A reason for this is explained in detail below.
First, the maximum value of the luminance of a blue light on the display surface of a liquid crystal panel is determined by the transmittance of a color filter (blue filter) of the liquid crystal panel through which the blue light travels (including a decrease in luminance that occurs when the blue light travels through an optical member such as an optical sheet or a diffuser between the LED light source and the liquid crystal panel) and the light intensity of the blue light emitted from the blue LED of a white LED (Light Intensity×Transmittance). On the other hand, even a white LED having its chromaticity classified into a predetermined chromaticity rank range as described above has a deviation of about ±5 nm from the peak wavelength of the blue light component. Further, the shorter the wavelength is, the lower the transmittance of the color filter (blue filter) tends to be. For this reason, such a deviation from the peak wavelength of the blue light component causes a change in the maximum value of the luminance of a blue light on the display surface of a liquid crystal panel.
As shown in
For this reason, the amount of light that is cut by the blue filter varies between the blue light having a peak wavelength of 455 nm and the blue light having a peak wavelength of 445 nm. Specifically, the shorter the peak wavelength of a blue light is, the lower the transmittance of a blue filter becomes and, accordingly, the larger the amount of light that is cut by the blue filer becomes. Therefore, when a white light containing a blue light having a short peak wavelength travels through a color filter, the chromaticity of the white light shifts toward the yellow side to the extent that the amount of the blue light is small. Moreover, due to the influence of visual sensitivity, there is a further decrease in blue light component (i.e. there is an increase in ratio of a light component by the phosphor with respect to the light component of the blue light).
The respective spectra of the white LEDs as shown in
In order to avoid such inconvenience that the chromaticity shifts toward yellow in such a case where the peak wavelength of a blue light component is short, it is necessary to make a white balance adjustment to adjust the balance between the maximum brightness of a red and a green lights and the maximum brightness of a blue light that has undesirably been lower than the desired brightness. However, such a white balance adjustment creates a new problem of an overall decrease in display luminance of the liquid crystal panel.
Further, the visual sensitivity of a human being looking at pictures at the same chromaticity and the same luminance varies depending on the viewing angle. This phenomenon is generally called an areal effect of color, and Commission Internationale de l'Eclairage (CIE) defines spectral sensitivities in a 2-degree visual field and a 10-degree visual field, respectively. As for a liquid crystal panel, this phenomenon appears as a phenomenon in which the way a color looks varies depending on the screen size of the liquid crystal panel or the distance between the viewer and the screen of the liquid crystal panel. In this phenomenon, unless the chromaticity of the white of an LED light source does not conform to a situation in which the viewer is seeing an image that is displayed on the liquid crystal panel, a white balance adjustment is required as in the aforementioned case. This creates a problem of a decrease in maximum luminance after all.
The present invention has been made in view of the foregoing problems, and it is an object of the present invention to provide white LEDs that do not raise the need to make a big white balance adjustment that leads to a decrease in luminance of a display on a liquid crystal panel and that have been selected so that a variation in chromaticity on the panel display falls within a desired range.
In order to solve the foregoing problems, an LED classification method according to the present invention is a method for classifying LEDs, the LEDs each including a combination of an LED element that emits a primary light and phosphor that, upon excitation by the primary light, emits a secondary light having a longer wavelength than the primary light, the LEDs each emitting a combined light of the primary light and the secondary light, those ones of the LEDs whose primary lights have their chromaticities falling within a predetermined chromaticity range being classified as LEDs for use in a backlight of a liquid crystal display apparatus, the method including: a chromaticity correcting step of calculating, for all of the LEDs to be classified, correction values for the chromaticities as based on transmission of the primary lights through a color filter in the liquid crystal display apparatus, and of correcting the chromaticities as corrected chromaticities on a basis of the correction values for all of the LEDs to be classified; and a chromaticity rank classification step of classifying the LEDs according to chromaticity rank on a basis of the corrected chromaticities.
Further, an LED classification device according to the present invention is an LED classification device for classifying LEDs, the LEDs each including a combination of an LED element that emits a primary light and phosphor that, upon excitation by the primary light, emits a secondary light having a longer wavelength than the primary light, the LEDs each emitting a combined light of the primary light and the secondary light, those ones of the LEDs whose primary lights have their chromaticities falling within a predetermined chromaticity range being classified as LEDs for use in a backlight of a liquid crystal display apparatus, the LED classification device including: chromaticity correcting means for calculating, for all of the LEDs to be classified, correction values for the chromaticities as based on transmission of the primary lights through a color filter in the liquid crystal display apparatus, and for correcting the chromaticities as corrected chromaticities on a basis of the correction values for all of the LEDs to be classified; and chromaticity rank classification means for classifying the LEDs according to chromaticity rank on a basis of the corrected chromaticities.
In the foregoing configuration, the chromaticity correcting step or the chromaticity correcting means calculates, for all of the LEDs to be classified, correction values for the chromaticities as based on the assumption that the primary lights have traveled through the color filter, and corrects chromaticities as corrected chromaticities on the basis of the correction values for all of the LEDs to be classified. Then, the chromaticity rank classification step or the chromaticity rank classification means classifies the LEDs according to chromaticity rank.
Such classification according to chromaticity rank with use of corrected chromaticities makes it possible to more appropriately classify the LEDs according to chromaticity rank on the basis of the prediction of a change in intensity of light by the color filter. Mounting in the respective backlights of liquid crystal display apparatuses of LEDs selected on the basis of such classification according to chromaticity rank makes it possible to suppress variation in luminance of light having traveled through the color filter from the backlight.
Thus configured, the LED classification method according to the present invention brings about an effect of making it possible to easily select LEDs that do not need to be made lower in luminance even when mounted in a backlight.
An embodiment of the present invention is described below with reference to
[Liquid Crystal Display Apparatus]
(Configuration of a Liquid Crystal Display Apparatus)
As shown in
The backlight 3 is an edge-light backlight, placed on the back side of the liquid crystal panel 4, which illuminates the whole surface of the liquid crystal panel 4, and has a plurality of light-emitting devices 5 and a light guide plate 6. The light-emitting devices 5 are white LEDs, mounted at predetermined intervals on the sides of the light guide plate 6, which emits light toward the light guide plate 6. As mentioned above, each of the white LEDs includes a blue LED and a red and a green phosphors that are excited by blue light from the blue LED. The light guide plate 6 deflects lights emitted from the light-emitting devices 5 so that the lights exit toward the light crystal panel 4.
The liquid crystal panel 4, constituted by filling the space between two opposed transparent substrates with liquid crystals, changes the transmittance of light from the backlight 3 by changing the alignment of the liquid crystals in units of matrices of pixels. Further, the liquid crystal panel 4 has a color filter 7 placed on the display surface side. The color filter 7 has filters formed for their respective colors of red (R), green (G), and blue (B) for every three subpixels constituting a pixel, and the filters have transmission spectra shown in
As shown in
The backlight 8 is a direct backlight, placed on the back side of the liquid crystal panel 4, which illuminates the whole surface of the liquid crystal panel 4, and has a plurality of light-emitting devices 5 and a mounting substrate 9. The light-emitting devices 5 are mounted at predetermined intervals on the whole surface of the mounting substrate 9 and emit direct light to the liquid crystal panel 4. Since this backlight 8 can modulate brightness for each small region (e.g., a pixel), it is excellent in energy saving and can increase the contrast ratio between light and dark.
(Configuration of an LED)
The LED 10 shown in
The frame body 11 is placed on the lead frame 13. Further, the frame body 11 is made of a nylon-based material and has a depressed portion 11a. The depressed portion 11a has an inclined surface formed as a reflecting surface that reflects light emitted by the LED chip 12. It is preferable that in order to efficiently take out the light emitted by the LED chip 12, the reflecting surface be made of a metal film containing silver or aluminum.
The lead frame 13 is insert-molded in the frame body 11. The lead frame 13 has a top end formed in a divided manner, with a part thereof exposed on the bottom surface of the depressed portion 11a of the frame body 11. Further, the lead frame 13 has a bottom end forming an external terminal by being cut into a predetermined length and bent along the outside wall of the frame body 11.
The LED chip 12 (LED element) is for example a GaN semiconductor light-emitting element having a conductive substrate, and has a bottom electrode formed on the bottom surface of the conductive substrate and has a top electrode formed on the other surface. Light (primary light) emitted by the LED chip 12 is a blue light that falls within the range of 430 to 480 nm and has its peak wavelength at 450 nm. Further, the LED chip 12 is die-bonded with conductive brazing filler metal to one side of the top end of the lead frame 13 that is exposed on the bottom surface of the depressed portion 11a. Furthermore, the LED chip 12 has its top electrode wire-bonded to the other side of the top end of the lead frame 13 via the wire 14. In this way, the LED chip 12 is electrically connected to the lead frame 13.
The resin 15 seals in the depressed portion 11a by being charged into the depressed portion 11a. Further, the resin 15 is preferably silicone resin, as it is required to be highly durable against the short-wavelength primary light.
The phosphors 16 and 17 are scattered across the resin 15. The phosphor 16 is a green phosphor that emits a green secondary light (having a peak wavelength of 500 nm or longer to 550 nm or shorter) that is longer in wavelength than the primary light, and is for example made of a Eu-activated sialon phosphor material. Meanwhile, the phosphor 17 is a red phosphor that emits a red secondary light (having a peak wavelength of 600 nm or longer to 780 nm or shorter) that is longer in wavelength than the primary light, and is for example made of a phosphor material obtained by combining CaAlSiN3:Eu. The use of such phosphors 16 and 17 makes it possible to obtain a three band LED 10 with good color rendering properties.
In the LED 10 thus configured, as the primary light emitted from the LED chip 12 passes through the resin 15, a portion of the primary light excites the phosphors 16 and 17 to be converted into a secondary light. The emitted light (combined light) obtained by mixing the primary light and the secondary light is radiated outward substantially in the form of a white light.
As shown in
[LED Classification Device]
The LED classification device 21 shown in
(Configuration of the Memory, the Storage Section, and the Display Section)
The memory 22 is a volatile memory in which to temporarily store characteristics measurement values obtained by an LED characteristics measuring device 31 measuring the characteristics of the LEDs 10 or in which to temporarily store arithmetic data generated through arithmetic processing by the arithmetic processing section 25. The characteristics measurement values are values which, for all of the LEDs 10 to be classified, are stored in the memory 22 in association with codes so assigned to the respective LEDs 10 that the LEDs 10 can be identified. The LED characteristics measuring device 31 is a device that measures the characteristics of the LEDs 10. The LED characteristics measuring device 31 measures the chromaticity, peak wavelength, etc. of each LED 10 with a large number of LEDs 10 emitting light and output the chromaticity, peak wavelength, etc. of each LED 10 as characteristics measurement values.
The storage section 23 is a storage device in which to save results of classification of the LEDs 10 as obtained through arithmetic processing by the arithmetic processing section 25, and is constituted by a hard disk device and the like.
The display section 24 is a display device for displaying the results of classification.
(Configuration of the Arithmetic Processing Section)
The arithmetic processing section 25 performs a process for classifying the LEDs 10 on the basis of the characteristics measurement values obtained from the LED characteristics measuring device 31. The arithmetic processing section 25 uses the following arithmetic expressions to correct the chromaticities (x,y) of light emitted by the LEDs 10 to be corrected chromaticities (x1,y1) based on the assumption that the light emitted by the LED 10 has traveled through the aforementioned color filter 7 (blue filter) (chromaticity correcting means). Further, the arithmetic processing section 25 classifies the LEDs 10 according to chromaticity rank on the basis of the corrected chromaticities (x1,y1).
It should be noted here that the chromaticities (x,y) and the corrected chromaticities (x1,y1) are chromaticities obtained through conversion by a common 2-degree visual field color matching function. Apart from these, for all of the chromaticities (x,y) and the corrected chromaticities (x1,y1), chromaticities obtained through conversion of spectral data by a 10-degree visual field color matching function may be used. Therefore, the arithmetic processing section 25 may correct the chromaticities with a 10-degree visual field color matching function.
Light emitted by a flat surface light source that is used in a television or the like may look in different colors depending on the situation in which a person actually sees the light. This is because the way a color looks varies depending on the visual-field range. In general, in the case of a calculation of the chromaticity of a light source that is used in a display, a chromaticity adjustment is made by using a 10-degree visual field color matching function rather than a 2-degree visual field color matching function. It is preferable to employ such a method to homogenize chromaticity, as the method causes a color to look uniform to a human being.
Specifically, the 2-degree visual field is to determine a color in the situation in which a viewer sees a sample having a diameter of 1.7 cm at a distance of 50 cm, and the 10-degree visual field is to determine a color in the situation where the viewer sees a sample of 8.7 cm at the same distance. It is appropriate that the 2-degree visual field is used for a viewing angle of 1 to 4 degrees and the 10-degree visual field is used for a viewing angle of greater than 4 degrees.
A chromaticity adjustment made by using the 10-degree visual field color matching function is applied to chromaticity correction based on the assumption of the blue filter, but can also be applied to chromaticity correction not based on the assumption of a blue filter.
According to Table 1, in a case where the viewer looks at a 14-inch or larger display at a distance of 5 m (5000 mm), it is appropriate to use a 10-degree visual field. With a common viewing position at a distance of 100 cm to 300 cm from the display and with the common size of a display for use in a television being 21 inches or larger, it seems to be appropriate evaluate the chromaticity of the display in a 10-degree visual field. Further, in the case of looking at a display for use in a personal computer, with a common viewing position at a distance of 50 cm to 100 cm from the display and with the common size of the display being 14 inches, it also seems to be appropriate to evaluate the chromaticity of the display in a 10-degree visual field.
It should be noted that on the assumption that light emitted from a light-emitting device 5 has traveled through the color filter 7 (blue filter), a correction is made in consideration of a change in chromaticity that happens until the emitted light travels through the liquid crystal panel 4. This change in chromaticity is a change in chromaticity with respect to the chromaticity of the emitted light in a case where the light emitted from the light-emitting device 5 has traveled through optical members such as a diffuser, an optical sheet, and a light guide plate, the color filter 7 (blue filter), and the liquid crystal panel 4. This causes the correction to be a more preferable correction that is more suitable for an actual display on the liquid crystal panel 4.
Further, in the present embodiment, as described above, a correction to the transmission characteristics of the color filter 7 is a correction to the transmission characteristics of a blue filter. This is because, as mentioned above in section “Technical Problem”, the fact that a deviation of the peak wavelength of a blue light component in light emitted from a light-emitting device 5 is large at a mass-production level of the light-emitting device 5 significantly affects the difference between the chromaticity of the emitted light before the transmission of the emitted light through the color filter 7 and the chromaticity of the emitted light after the transmission of the emitted light through the color filter 7. Regarding this, correcting the transmission characteristics of the red and the green filters achieves a correction that is more suitable for an actual display on the liquid crystal panel. However, a method for correcting only the transmission characteristics of the blue filter can be said to be a simple method for correcting measured data on the light-emitting device 5 with simple correction formulas such as those mentioned below. Further, since this correction method can eliminate the need for rank classification regarding blue light peaks, it can reduce the number of characteristics classification items (control characteristics items) of the light-emitting device 5.
x1=x−α×(λp−λ0)
y1=y=β×(λp−λ0)
In the foregoing arithmetic expressions, λp is the measured value of the peak wavelength of a blue light component in light emitted by an LED 10. Since the effect of a blue light on the chromaticity is exerted not only on the peak wavelength but also on the spectral shape, this measured value is not a maximum point of emission intensity but a measured value of a dominant wavelength with the emission spectral shape taken into account. Measurement of the dominant wavelength is performed by measuring the dominant wavelength as a blue monochromatic light by, for example, extracting an emission spectrum of 480 nm or shorter. This measurement takes into account the effect of absorption of the blue LED light inside the light-emitting device 5 into the phosphors.
λ0 is the center value (average wavelength of variations) of measured values of this peak wavelength, and is set in the range of 445 nm to 450 nm. While this wavelength is calculated on the basis of the peak wavelengths of blue lights of all of the LEDs 10, it is desirable that this wavelength be calculated as an average value with respect to the total number or more of LEDs 10 that are used as a single set in the respective backlights 3 and 8 of the liquid crystal display apparatuses 1 and 2.
α and β are coefficients, and are set in the range of 0 to 0.01.
The chromaticities (x,y) and the peak wavelength λp are obtained as characteristic measurement values of an LED 10 from the LED characteristics measuring device 31.
In order to achieve the foregoing process, the arithmetic processing section 25 has a coefficient calculating section 26, a corrected chromaticity calculating section 27, and a chromaticity rank classification section 28.
<Configuration of the Coefficient Calculating Section>
The coefficient calculating section 26 (coefficient calculating means) calculates the coefficients of α and β of the arithmetic expressions on the basis of the chromaticities (x,y) and the peak wavelength λp as characteristics measurement values from the LED characteristics measuring device 31 as stored in the memory 22. Specifically, the coefficient calculating section 26 performs the following process.
(1) The coefficient calculating section 26 runs a simulation to find, on the basis of the mutually different peak wavelengths λp of two LEDs 10, the chromaticity based on the assumption that a light having the average wavelength λ0 has traveled through the color filter 7. The simulation used here is based on a function of the transmittance of the color filter 7. Specifically, the coefficient calculating section 26 performs the process of finding the transmittance with respect to the average wavelength λ0 from this function and calculating the chromaticity on the basis of a light intensity obtained by multiplying the transmittance by a light intensity with respect to the average wavelength λ0. Further, the two peak wavelengths λp are the peak wavelengths λp of two LEDs 10 that are identical in chromaticity of combined light, and are peak wavelengths λp deviating from the average wavelength λ0, with the average wavelength λ0 as the center. This deviation from the average wavelength λ0 is a maximum value of about ±5 nm. Further, the coefficient calculating section 26 finds the average wavelength λ0 by calculating the average of the peak wavelengths λp of all of the LEDs 10 as stored in the memory 22, and stores the average wavelength λ0 in the memory 22.
(2) By using, as a reference chromaticity, the chromaticities thus found, the coefficient calculating section 26 runs a simulation to find the amounts of change Δx and Δy from the reference chromaticity (x0,y0) of chromaticity with respect to the two peak wavelengths Δp. The simulation used here is based on a function of the transmittance of the color filter 7. Specifically, the coefficient calculating section 26 performs the process of finding the respective transmittances with respect to the two peak wavelengths λp from this function, calculating the chromaticities on the basis of a light intensity obtained by multiplying the transmittance by a light intensity with respect to the two peak wavelengths Δp, and calculating the differences between the chromaticities and the reference chromaticity (x0,y0) as the amounts of change Δx and Δy.
(3) As shown in
<Configuration of the Corrected Chromaticity Calculating Section>
The corrected chromaticity calculating section 27 (corrected chromaticity calculating means) applies the coefficients α and β stored in the memory 22 to the arithmetic expressions to compute the corrected chromaticities (x1,y1) according to the arithmetic expressions with respect to the peak wavelengths λp concerning all of the LEDs 10 as read out from the memory 22. The corrected chromaticity calculating section 27 stores, in the memory 22, the corrected chromaticities (x1,y1) thus calculated.
In each of the arithmetic expressions, (λp−λ0) is the difference (wavelength shift amount) between the peak wavelength λp and the average wavelength λ0, and as shown in
<Configuration of the Chromaticity Rank Classification Section>
The chromaticity rank classification section 28 (chromaticity rank classification means) reads out the corrected chromaticities (x1,y1) from the memory 22 and classifies the LEDs 10 according to chromaticity rank on the basis of the chromaticities (x1,y1).
The frame F is divided into smaller ranges configured such that demarcations can be made according to rank for each division. In this frame F, the corrected chromaticities (x1,y1) of the group of LEDs 10 the wavelengths of whose blue lights are short are distributed in a range D1 indicated by a solid line. In the range D1, the peak wavelength is 444.7 nm, and the average AVE1 of chromaticity is in a position indicated by a solid circle. Meanwhile, in the frame F, the chromaticities of the group of LEDs 10 the wavelength of whose blue lights are long are distributed in a range D2 indicated by a broken line. In the range D2, the peak wavelength is 446.2 nm, and the average AVE2 of chromaticity is in a position indicated by a broken circle.
<Realization Form of the Arithmetic Processing Section>
The blocks of the arithmetic processing section 25, namely the coefficient calculating section 26, the corrected chromaticity calculating section 27, and the chromaticity rank classification section 28, are realized by software (LED classification program) as executed by a CPU as follows: This LED classification program causes a computer to function as the LED classification device 21 (the coefficient calculating section 26, the corrected chromaticity calculating section 27, and the chromaticity rank classification section 28).
Alternatively, each of the blocks described above may be constituted by hardware logic, or may be realized by processing by program with a DSP (digital signal processor).
Program code (executable program, intermediate code program, or source program) for the software may be stored in a computer-readable storage medium. The objective of the present invention can also be achieved by mounting the storage medium to the LED classification device 21 in order for the CPU to retrieve and execute the program code contained in the storage medium.
The storage medium may be, for example, a tape, such as a magnetic tape or a cassette tape; a magnetic disk, such as a floppy (Registered Trademark) disk or a hard disk, or a disk, including an optical disk such as CD-ROM/MO/MD/BD/DVD/CD-R; a card, such as an IC card (memory card) or an optical card; or a semiconductor memory, such as a mask ROM/EPROM/EEPROM (Registered Trademark)/flash ROM.
The LED classification device 21 may be arranged to be connectable to a communications network so that the program code may be delivered over the communications network. The communications network is not limited in any particular manner, and may be, for example, the Internet, an intranet, extranet, LAN, ISDN, VAN, CATV communications network, virtual dedicated network (virtual private network), telephone line network, mobile communications network, or satellite communications network. The transfer medium which makes up the communications network is not limited in any particular manner, and may be, for example, wired line, such as IEEE 1394, USB, electric power line, cable TV line, telephone line, or ADSL line; or wireless, such as infrared radiation (IrDA, remote control), Bluetooth (Registered Trademark), 802.11 wireless, HDR, mobile telephone network, satellite line, or terrestrial digital network.
(Process of LED Classification by the LED Classification Device)
A process of classification of the LEDs 10 by the LED classification device 21 is described with reference to
As shown in
Furthermore, by using the aforementioned arithmetic expressions and the coefficients α and β, the LED classification device 21 calculates the corrected chromaticities (x1,y1) (step 3: corrected chromaticity calculating step, chromaticity correcting step. At this step, for all of the LEDs 10 to be classified, the corrected chromaticity calculating section 27 calculates the corrected chromaticities (x1,y1) by using the measured chromaticities (x,y) and the peak wavelength λp for all of the LEDs 10 to be classified.
Then, the LED classification device 21 classifies the LEDs 10 according to chromaticity rank on the basis of the corrected chromaticities (x1,y1) (step 4: chromaticity rank classification step). At this step, the chromaticity rank classification section 28 classifies the LEDs 10 according to chromaticity rank in accordance with whether or not the corrected chromaticities (x1,y1) are distributed in the frame F shown in
[Effects of the LED Classification Device]
As described above, the LED classification device 21 is configured to use the arithmetic processing section 25 to correct, as the corrected chromaticities (x1,y1), the chromaticities (x,y) after transmission through the color filter 7 and classify the LEDs 10 according to chromaticity rank on the basis of the corrected chromaticities (x1,y1).
Thus, for those LEDs 10 whose peak wavelengths λp have deviated toward the longer side, the corrected chromaticities (x1,y1) are calculated so that the chromaticities (x,y) shifts toward blue (lower chromaticity) (c.f. the average AVE2 in
Moreover, by using the corrected chromaticities (x1,y1) thus corrected, the LEDs 10 can be classified according to chromaticity rank on the basis of the prediction of a decrease (shift amount) in intensity of blue light by the color filter 7. By mounting, on the respective backlights 3 and 8 of the liquid crystal display apparatuses 1 and 2, the LEDs 10 selected according to such chromaticity rank classification, variations in luminance of blue light on the liquid crystal panel 4 can be suppressed. In particular, the light emitted by the LEDs 10 whose peak wavelengths λp are short have its blue light component cut by the color filter 7 when it travels through the liquid crystal panel 4 (color filter 7), so that the chromaticity shifts more toward the yellow side. Therefore, by making the chromaticity correction, chromaticity rank classification more suitable as a light source for use in a liquid crystal panel can be performed.
It should be noted that since the yield of LEDs 10 ranked in the center of the frame F shown in
[Addition]
Since the LEDs 10 contains the phosphors 16 and 17, the emission spectrum also contains the color components of the phosphors. This allows the LED characteristics measurement device 31 to obtain a wavelength of blue light by measuring a peak wavelength. However, the measurement of a peak wavelength is easily noised and is therefore susceptible to error. To diminish the effect of noise, it is only necessary for the LED characteristics measurement device 31 to designate a range of wavelengths from 400 nm to a longer wavelength where the color components of the phosphors do not appear, and to calculate a dominant wavelength in this range of wavelengths. As mentioned earlier, for example, a dominant wavelength as blue monochromatic light is measured by extracting an emission spectrum of 480 nm or shorter. This measurement takes into account the effect of absorption of the blue LED light inside the light-emitting device 5 into the phosphors.
(Addition)
An LED classification method and an LED classification device according to the present embodiment can also be expressed as follows:
An LED classification method is a method for classifying LEDs, the LEDs each including a combination of an LED element that emits a primary light and phosphor that, upon excitation by the primary light, emits a secondary light having a longer wavelength than the primary light, the LEDs each emitting a combined light of the primary light and the secondary light, those ones of the LEDs whose primary lights having their chromaticities falling within a predetermined chromaticity range being classified as LEDs for use in a backlight of a liquid crystal display apparatus, the method including: a chromaticity correcting step of calculating, for all of the LEDs to be classified, correction values for the chromaticitites as based on transmission of the primary lights through a color filter in the liquid crystal display apparatus, and of correcting the chromaticities as corrected chromaticities on a basis of the correction values for all of the LEDs to be classified; and a chromaticity rank classification step of classifying the LEDs according to chromaticity rank on a basis of the corrected chromaticities.
Further, an LED classification device is an LED classification device for classifying LEDs, the LEDs each including a combination of an LED element that emits a primary light and phosphor that, upon excitation by the primary light, emits a secondary light having a longer wavelength than the primary light, the LEDs each emitting a combined light of the primary light and the secondary light, those ones of the LEDs whose primary lights having their chromaticities falling within a predetermined chromaticity range being classified as LEDs for use in a backlight of a liquid crystal display apparatus, the LED classification device including: a chromaticity correcting section for calculating, for all of the LEDs to be classified, correction values for the chromaticities as based on transmission of the primary lights through a color filter in the liquid crystal display apparatus, and for correcting the chromaticities as corrected chromaticities on a basis of the correction values for all of the LEDs to be classified; and a chromaticity rank classification section for classifying the LEDs according to chromaticity rank on a basis of the corrected chromaticities.
The LED classification method may be preferably configured such that the chromaticity correcting step includes: a coefficient calculating step of calculating an average wavelength of peak wavelengths of the primary lights as obtained for all of the LEDs to be classified, of calculating a reference chromaticity as of a time when a primary light having the average wavelength has traveled through the color filter and amounts of change in the chromaticities with respect to the reference chromaticity, and of calculating, as coefficients of the correction values for the chromaticities, inclinations of the amounts of change with respect to a shift amount of each of the peak wavelengths from the average wavelength, respectively; and a corrected chromaticity calculating step of calculating the correction values by multiplying a difference between the peak wavelength and the average wavelength by the coefficients, respectively, and of calculating the corrected chromaticities by subtracting the correction values from the chromaticities obtained for all of the LEDs to be classified, respectively.
The LED classification device may be preferably configured such that the chromaticity correcting section includes: a coefficient calculating section for calculating an average wavelength of peak wavelengths of the primary lights as obtained for all of the LEDs to be classified, for calculating a reference chromaticity as of a time when a primary light having the average wavelength has traveled through the color filter and amounts of change in the chromaticities with respect to the reference chromaticity, and for calculating, as coefficients of the correction values for the chromaticities, inclinations of the amounts of change with respect to a shift amount of each of the peak wavelengths from the average wavelength, respectively; and a corrected chromaticity calculating section for calculating the correction values by multiplying a difference between the peak wavelength and the average wavelength by the coefficients, respectively, and for calculating the corrected chromaticities by subtracting the correction values from the chromaticities obtained for all of the LEDs to be classified, respectively.
In the foregoing configuration, since the coefficients of the correction values are calculated in the coefficient calculating step or by the coefficient calculating section on the basis of the inclinations of the amounts of change in chromaticity with respect to the reference chromaticity obtained on the basis of the assumption that the primary light has traveled through the color filter, a change in chromaticity due to the transmission of the primary light through the color filter is reflected in the correction values. Moreover, in the corrected chromaticity calculating step or by the corrected chromaticity calculating section, the corrected chromaticities are calculated by subtracting, from the chromaticities, the correction values thus obtained.
This makes it possible to easily cause a change in chromaticity by the color filter to be reflected in chromaticity correction.
The LED classification method or the LED classification device is preferably configured such that the primary lights are blue lights.
As for the blue lights, as mentioned earlier, due to variations in peak wavelength among the LEDs, the intensity of light having traveled though the color filter varies, with the result that display colors are affected. To this, as mentioned earlier, by correcting the chromaticity on the basis of the prediction of a change due to transmission through the color filter, the LEDs can be properly classified according to chromaticity rank on the basis of a change in chromaticity distribution by the color filter.
The LED classification method or the LED classification device is preferably configured such that the chromaticity correcting step or the chromaticity correcting means corrects the chromaticities by using a 10-degree visual field color matching function.
Correction of the chromaticities with a 10-degree visual field color matching function leads to homogenization of chromaticity observed by the human eye. Therefore, a color is produced which looks uniform to the human eye, and an adjustment is made so that desired chromaticity is attained.
Further, an LED classification program is a program for causing a computer to functions as each of the sections of the LED classification device. Further, a storage medium is a computer-readable storage medium having the LED classification program stored therein. The LED classification program and the storage medium are encompassed in the technical scope of the present embodiment.
The present embodiment has been described in terms of classification of LEDs 10 each including a green phosphor and a red phosphor. However, the phosphors that the LEDs 10 each include are not so limited. For example, the LEDs 10 may each include, instead of including a green phosphor and a red phosphor, a yellow phosphor that is excited by a blue light of a blue LED. This makes it possible to obtain pseudo-white through a mixture of the blue light of the blue LED and the yellow light of the yellow phosphor.
While, in the present embodiment, the LED characteristics measurement device 31 is provided outside the LED classification device 21, the LED characteristics measurement device 31 may alternatively be provided as a part of the LED classification device 21.
The present invention is not limited to the description of the embodiments above, but may be altered by a skilled person within the scope of the claims. An embodiment based on a proper combination of technical means disclosed in different embodiments is encompassed in the technical scope of the present invention.
An LED classification method according to the present invention is suitably applicable to a liquid crystal display apparatus using LEDs as a backlight, as the method corrects the chromaticities of LEDs on the basis of the prediction of a change in luminance of light having traveled through a color filter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-019151 | Jan 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/066300 | 6/26/2012 | WO | 00 | 7/30/2014 |
