CN101839423B - Method for improving brightness uniformity of LED backlight - Google Patents

Abstract

The invention discloses a method for improving the brightness uniformity of LED backlight sources. According to the relationship between the characteristic parameters of the LEDs used and the optical system of the backlight source, the brightness distribution function of the LED in the backlight source module is measured and calculated, and further calculated The arrangement distance and arrangement mode of the LEDs in the backlight source are obtained, thereby improving the uniformity of the brightness of the LED backlight source.

Description

A method for improving the brightness uniformity of LED backlight

technical field

The invention relates to a method for improving the brightness uniformity of a light-emitting diode (hereinafter referred to as LED) backlight of a liquid crystal display (hereinafter referred to as LCD), in particular to an LED backlight with uniform brightness of the entire screen obtained by arranging LEDs at unequal intervals.

Background technique

At present, liquid crystal display (LCD) has become the mainstream flat panel display device. However, since the liquid crystal itself does not have the characteristic of emitting light, the backlight has become an indispensable and important part of the liquid crystal display. The performance of the backlight directly determines the brightness and color of the liquid crystal display. Efficiency, power consumption and other indicators. The most widely used LCD backlight is the cold cathode fluorescent lamp (CCFL), but in comparison, the use of light-emitting diodes (LED) as the LCD backlight has low driving voltage, low power consumption, good color reproduction, and environmental adaptability. Strong, no mercury pollution and other advantages. At present, there are two types of LED backlight structures for LCDs: side-type and direct-type. The side-type is generally used for small and medium-sized liquid crystal displays, and the LED backlight for large-size LCDs is generally a direct-type structure.

In the application of LED backlight, whether it is a side-type or a direct-type structure, the arrangement spacing of LEDs is generally uniform, so that the full-screen brightness uniformity of the LED backlight, especially the brightness of the edge of the backlight is significantly lower than that of the LED backlight. other areas. The main purpose of this patent is to propose a method for arranging LEDs non-uniformly by using the luminous characteristics of LEDs and the relationship between them and the optical system of the backlight source, so as to improve the brightness uniformity of the LED backlight source.

Contents of the invention

The purpose of the present invention is to propose a method for improving the brightness uniformity of LED backlight sources, reduce costs, and improve the brightness of LED backlight sources.

The LED arrangement method that the present invention proposes is realized like this:

According to the characteristic parameters of the LED and the characteristics of the optical system of the backlight module, measure the brightness distribution function of the LED, calculate the brightness of any point in the backlight, and obtain the LED lamp under the condition that the brightness uniformity of any point meets the design requirements The arrangement spacing and arrangement method, the specific steps are:

(1) First, according to the number n of LEDs required by the backlight device and the size of the LED backlight, calculate the distance between the LEDs when the LEDs are evenly arranged. is d, and the uniform arrangement spacing of LEDs is a=d/(n-1); in the direct-lit backlight device, the size of the LED backlight is l (length)×w (width), and the number of LEDs arranged in the long direction is na and the number nb of LEDs arranged in the width direction satisfy na×nb=n, then the arrangement spacing of LEDs in the length and width directions are l/(na-1) and w/(nb-1) respectively;

(2) According to the luminous flux Φi of a single LED and the number n of LEDs used in the backlight, calculate the total luminous flux Φ=nΦi of the LED backlight, and then calculate the average value of the LED backlight according to the transmittance parameters of the optical system of the backlight If the brightness is L, the brightness uniformity of the LED backlight requires that the brightness change range of the whole screen be L±ΔL (ΔL=7.5%L);

(3) Use a color analyzer to measure the brightness distribution function of a single LED after passing through the backlight optical system. The specific method is: take the LED as the center, select several test points in the horizontal, vertical and other directions, and measure its brightness value , then obtain the luminance distribution function L=f(x, y) of LED by fitting, x and y are respectively taking LED as the center, the distance coordinates of any point on the plane to the LED, and L is the brightness of any point;

(4) Calculation of LED non-uniform arrangement spacing. It is known that the size of a single LED is la (length) × lb (width). First, place the first LED on the edge of the backlight (taking the horizontal direction as an example). The distance between the centers of two LEDs may be any value between la(lb) and l/2. According to the actual application requirements, the step size of the change of the LED arrangement distance is Δl, that is, the possible value of the distance between any two LED arrangements is la, la+Δl, la+2Δl, la+3Δl..., until the end of l/2, the horizontal and vertical arrangements are symmetrical;

When the number na of LEDs is an odd number, the center position is k=(na-1)/2+1. The brightness value calculation method of any point is as follows:

for Di＝la:Δl:l/2;

i is taken from 1 to k-1, and the possible arrangement distance Di of the i-th and i+1-th LEDs is obtained;

Dk=Dk-1, Dk+1=Dk-2...Dna-1=D1;

Li=f(1)+f(2)+f(3)...+f(na);

i ranges from 1 to na, Li represents the brightness value of the i-th point, and f(j) represents the brightness value of the j-th LED at point i;

When the number na of LEDs is an even number, the center position is between k=na/2 and k+1. The brightness value calculation method of any point is as follows:

for Di＝la:Δl:l/2;

i is taken from 1 to k, and the possible arrangement distance Di of the i-th and i+1-th LEDs is obtained;

Dk+1=Dk-1, Dk+2=Dk-2...Dna-1=D1;

Li=f(1)+f(2)+f(3)...+f(na);

i ranges from 1 to na, Li represents the brightness value of the i-th point, and f(j) represents the brightness value of the j-th LED at point i;

The formula for calculating the spacing in the vertical direction is similar to that in the horizontal direction, except that the possible values of the spacing between any two LEDs are lb, lb+Δl, lb+2Δl, lb+3Δl..., until the end of l/2,

The uniformly arranged LEDs are adjusted according to the calculated arrangement spacing in the horizontal and vertical directions, so as to obtain an LED backlight with uniform brightness.

As a simplification of the present invention, the non-uniform arrangement of LEDs in both the side-entry type and the direct-lit type can be arranged non-uniformly and symmetrically along the horizontal and vertical directions based on the center of the backlight source. In addition, in order to meet the needs of dynamic dimming of the LED backlight source, the LEDs can be arranged first, and then the regions can be divided.

According to the characteristic parameter and brightness distribution function of the LED lamp tube, the invention improves the brightness uniformity of the LED backlight without changing the optical system of the LED backlight module, without increasing the cost, and only changing the arrangement of the LEDs.

Description of drawings

FIG. 1 is a schematic structural view of a single-side side-entry backlight device for a liquid crystal display;

Fig. 2 is a schematic structural diagram of a double-side side-entry backlight device for a liquid crystal display;

FIG. 3 is a schematic diagram of the arrangement structure of LEDs in a side-entry backlight device;

4 is a schematic structural diagram of a direct-type backlight device for a liquid crystal display;

5 is a schematic structural view of an embodiment of a direct-type backlight device;

The content of the present invention will be described in further detail below in conjunction with the accompanying drawings.

Detailed ways

1 and 2, the side-lit backlight module includes a reflector 120, a light guide plate 130, a diffusion plate 140 and an optical film 150, and the LED tube 110 can be placed on one side or both sides of the light guide plate. Can be white LED or multi-color LED. In the side-type backlight module, it is first necessary to calculate the required number of LED light tubes 110 according to the characteristic parameters of the LED light tubes 110 and the design index of the liquid crystal display.

Referring to FIG. 3 , the LED light tubes 110 are arranged at unequal intervals on the circuit board 160 , and all the LED light tubes 110 are placed at the same angle, which is one of the embodiments of this patent. Measure and calculate the horizontal luminance distribution function L=f(x) of the LED lamp tube 110 after passing through the reflector 120, the light guide plate 130, the diffusion plate 140 and the optical film 150, where x is any point on the circuit board 160 to the LED arrangement circuit The distance from the center of the plate 160, L is the brightness value. Then calculate the arrangement spacing x1, x2 .

Referring to Fig. 4, in the direct type backlight module, the LED lamp tube 110 is placed directly under the light guide plate 130, the LED lamp tube 110 can be a white LED or a multi-color LED, the reflector 120 is located on the circuit board 160, and the reflector is drilled to make The LED lamp tube 110 can be exposed. In the direct-lit backlight module, the number of required LED light tubes 110 must be calculated first according to the design index of the liquid crystal display and the characteristic parameters of the LED light tubes 110, and then the arrangement and arrangement distance of the LED light tubes 110 should be calculated.

Referring to Fig. 5, all the LED lamp tubes 110 of the direct-lit backlight are arranged non-uniformly in the horizontal and vertical directions, and the placement angles of all the LED lamp tubes 110 on the circuit board 160 are kept consistent, which is the principle of this patent. The second embodiment. In this embodiment, at first measure and calculate the luminance distribution function L=f(x, y) of the LED lamp tube 110 used after passing through the reflector 120, the light guide plate 130, the diffuser plate 140 and the optical film 150, wherein x is arbitrary in the horizontal direction. The distance from a point to the vertical line of the center of the LED backlight, y is the distance from any point in the vertical direction to the horizontal line of the center of the LED backlight, and L is the brightness value. Then according to the total number of LED lamp tubes 110 required by the backlight source, and the components of the brightness distribution function f(x, y) of a single LED lamp tube 110 in the horizontal direction and the vertical direction, the arrangement of the LED lamp tubes 110 in the horizontal direction is calculated respectively. The distance x1, x2...xn-1 and the arrangement distance y1, y2...ym-1 of the LED light tubes 110 in the vertical direction can be used to obtain the arrangement and arrangement distance of all the LED light tubes 110 in the entire backlight. By arranging the LED lamp tubes 110 at this pitch, a backlight with high brightness uniformity can be obtained.

The LED backlight arrangement method proposed by the present invention has the following advantages:

According to the characteristic parameters and brightness distribution function of the LED lamp tube, the optical system of the LED backlight module is not changed, only the arrangement of the LEDs is changed, so as to improve the performance of the backlight source, and at the same time, make the brightness uniformity of the backlight source better.

(1) First, according to the number n of LEDs required by the backlight device and the size of the LED backlight, calculate the distance between the LEDs when the LEDs are evenly arranged. In the side-type backlight device, the total length of the side of the backlight on which the LEDs are placed is d, and the uniform arrangement distance of the LEDs is a=d/(n-1). In the direct-type backlight device, the size of the LED backlight is l (length)×w (width), and the number of LEDs arranged in the length and width directions is respectively na×nb=n, then the number of LEDs in the length and width directions The arrangement pitches are l/(na-1) and w/(nb-1), respectively.

(2) According to the luminous flux Φi of a single LED and the number n of LEDs used in the backlight source, the total luminous flux Φ=nΦi of the LED backlight source is obtained, and then according to the parameters such as the transmittance of the backlight optical system, the value of the LED backlight source is obtained. If the average brightness is L, the brightness uniformity of the LED backlight requires that the brightness variation range of the whole screen be L±ΔL (ΔL=7.5%L).

(3) Use a color analyzer to measure the brightness distribution function of a single LED after passing through the backlight optical system. The specific method is: take the LED as the center, select several test points in the horizontal, vertical and other directions, measure their brightness values, and then obtain the LED brightness distribution function L=f(x, y), x and y by fitting They are the distance coordinates from any point on the plane to the LED with the LED as the center, and L is the brightness of any point.

(4) Calculation of LED non-uniform arrangement spacing. It is known that the size of a single LED is la (length) × lb (width), first place the first LED on the edge of the backlight (take the horizontal direction as an example), and the distance between the centers of two adjacent LEDs may be la (lb ) and l/2, according to the actual application requirements, the step size of the change of the LED arrangement spacing is Δl, that is, the possible values of the arrangement spacing of any two LEDs are la, la+Δl, la+2Δl, la+ 3Δl..., until the end of l/2, and the arrangement in both horizontal and vertical directions is symmetrical.

When the number na of LEDs is an odd number, the center position is k=(na-1)/2+1. The brightness value calculation method of any point is as follows:

for Di＝la:Δl:l/2; (possible spacing between the first and second LEDs)

for Di+1＝Di:Δl:l/2; (possible spacing between the second and third LEDs)

for Di+2＝Di+1:Δl:l/2; (possible spacing between the third and fourth LEDs)

...

for Dk-1＝Dk-2:Δl:l/2; (possible arrangement spacing of K-1 and K LEDs)

Dk=Dk-1, Dk+1=Dk-2...Dna-1=D1;

Li=f(1)+f(2)+f(3)...+f(na) (calculation method of brightness at any point)

When the number na of LEDs is an even number, the center position is between k=na/2 and k+1. The brightness value calculation method of any point is as follows:

for Di＝la:Δl:l/2; (possible spacing between the first and second LEDs)

for Di+1＝Di:Δl:l/2; (possible spacing between the second and third LEDs)

for Di+2＝Di+1:Δl:l/2; (possible spacing between the third and fourth LEDs)

...

for Dk-1＝Dk-2:Δl:l/2; (possible arrangement spacing of K-1 and K LEDs)

for Dk＝Dk-1:Δl:l/2; (possible arrangement spacing of the Kth and K+1th LEDs)

Dk+1=Dk-1, Dk+2=Dk-2...Dna-1=D1;

Li=f(1)+f(2)+f(3)...+f(na) (calculation method of brightness at any point)

If Li satisfies the requirement of luminance uniformity, record all the corresponding LED array spacing data sets as the array spacing database for calculating the luminance value of the second test point. Calculate the brightness value of the LED at the second test point according to the LED arrangement spacing database screened out by the first test point, and select the data group that makes the second test point meet the brightness uniformity as the brightness value of the third test point Computed permutation spacing database. By analogy, it is possible to obtain the LED array spacing data set that makes the last test point meet the brightness uniformity requirement, and also obtain the array data set that makes the brightness values of all test points meet the uniformity requirement. Among these data groups that meet the requirements, find the arrangement data group that minimizes the mean square error of the luminance values of all test points, which is the desired non-uniform LED arrangement spacing. The formula for calculating the spacing in the vertical direction is similar to that in the horizontal direction, except that the possible values of the spacing between any two LEDs are lb, lb+Δl, lb+2Δl, lb+3Δl... until l/2 ends.

(5) On the basis of calculating the non-uniform arrangement spacing of the LEDs, adjust the evenly arranged LEDs, so as to obtain an LED backlight with uniform brightness.

In the side-type backlight device, according to the one-dimensional distribution function of the brightness of the LED tubes along the circuit board, the arrangement spacing of the LED tubes along the direction of the circuit board is calculated. Usually, the arrangement spacing is unequal.

In the direct-type backlight device, according to the two-dimensional distribution function of the LED lamps, the arrangement distance and the arrangement mode of the LED lamps in the backlight are calculated to be arranged along the horizontal and vertical directions.

In the direct type backlight device, the LED backlight arranged in the horizontal direction and the vertical direction, the spacing between the LEDs arranged in the horizontal direction and the vertical direction are not equal.

In the direct-lit backlight device, the LEDs in the horizontal and vertical directions are arranged at unequal intervals, and the arrangement manners of the unequal intervals in the horizontal and vertical directions may be the same or different.

Claims (1)

1. method that improves LED-backlit source brightness uniformity, it is characterized in that: according to the characteristic parameter of LED and the optical system characteristics of backlight source module, measure the Luminance Distribution function of LED, calculate the brightness of arbitrfary point in the backlight, in the situation that the brightness uniformity that guarantees the arbitrfary point meets design requirement, obtain arrangement pitches and the arrangement mode of LED fluorescent tube, concrete steps are:

(1) at first, according to the required LED number n of backlight arrangement and the size in LED-backlit source, calculate LED distance between LED when evenly distributed, in the side entrance back source apparatus, the backlight side overall length of placing LED is d, and the uniform arrangement pitches of LED is a=d/ (n-1); In bottom lighting type backlight device, the LED-backlit source is of a size of long l * wide w, the LED quantity nb that arranges on the LED quantity na that length direction is arranged and the cross direction satisfies na * nb=n, and then the arrangement pitches of LED is respectively l/ (na-1) and w/ (nb-1) on length and the cross direction;

(2) the LED number n that adopts according to the luminous flux phi i of single LEDs and backlight asks for the total light flux Φ in LED-backlit source=n Φ i, then according to the transmitance parameter of backlight optical system, obtains the mean flow rate in LED-backlit source

Then the brightness uniformity in LED-backlit source requires full frame brightness excursion everywhere to be

Wherein $\mathrm{\ΔL}=7.5\%\stackrel{\‾}{L};$

(3) measure the Luminance Distribution function of single LEDs after the backlight optical system with color analysis instrument, concrete grammar is: centered by LED, choose respectively several test points in horizontal and vertical and other directions, measure its brightness value, then obtain Luminance Distribution function L=f(x, the y of LED by match), x and y are respectively centered by LED, any point is to the range coordinate of LED on the plane, and L is the brightness of arbitrfary point;

(4) calculating of the non-homogeneous arrangement pitches of LED, known single LEDs is of a size of long la * wide lb, take horizontal direction as example, at first place the first LEDs at the edge of backlight, the spacing at adjacent two LEDs centers may be the arbitrary value between la and the l/2, based on the actual application requirements, the step-length that the LED arrangement pitches changes is got Δ l, the probable value that is any two LEDs arrangement pitches is la, la+ Δ l, la+2 Δ l, la+3 Δ l ... until l/2 finishes, the arrangement of horizontal and vertical direction is symmetric arrays;

When LED number na was odd number, then the center was k=(na-1)/2+1, and the brightness value computational methods of arbitrfary point are as follows:

for?Di=la:Δl:l/2;

I gets 1 to k-1, tries to achieve the possible arrangement pitches Di of i and i+1 LEDs;

Dk=Dk-1,Dk+1=Dk-2……Dna-1=D1;

Li=f(1)+f(2)+f(3)…+f(na);

I gets 1 to na, and Li represents the brightness value that i is ordered, and f (j) represents j the brightness value that LED is ordered at i;

When LED number na was even number, then the center was between k=na/2 and k+1, and the brightness value computational methods of arbitrfary point are as follows:

for?Di=la:Δl:l/2;

I gets 1 to k, tries to achieve the possible arrangement pitches Di of i and i+1 LEDs;

Dk+1=Dk-1,Dk+2=Dk-2……Dna-1=D1;

Li=f(1)+f(2)+f(3)…+f(na)；

I gets 1 to na, and Li represents the brightness value that i is ordered, and f (j) represents j the brightness value that LED is ordered at i;

Distance computation formula and the horizontal direction of vertical direction are similar, and the probable value that is any two LEDs arrangement pitches is lb, lb+ Δ l, lb+2 Δ l, lb+3 Δ l ..., until the l/2 end,

Arrangement pitches according to calculating gained horizontal and vertical direction is adjusted evenly distributed LED, thereby obtains the LED-backlit source of brightness uniformity.

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