The so-called backlight should be a light source located behind the liquid crystal display, and its luminous effect will directly affect the visual effect of the liquid crystal display module. The liquid crystal display itself does not emit light. The graphics or characters it displays are the result of its modulation of the optical fiber, which has become the initial stage of the development of the backlight source. Now the backlight source has become an independent electronic discipline, and has gradually become a research and development hotspot.

Application of LED Backlight on LCD

In the current improvement of light efficiency, thereby increasing the ratio of screen output light to light source output light, improving the LCD light source is one of them. The main principle is that each sub-pixel of the LCD is illuminated only by its corresponding color element. , thereby eliminating the need for color filters and improving light efficiency.

1. Structure

In an LCD with a static illumination backlight, a microlens array is installed under the pixel layer, and each pixel corresponds to a microlens. In order to obtain sufficient brightness on the display screen and improve the uniformity of the display, a suitable refractive layer is provided in the light guide plate.

2. LCD backlight characteristics for static lighting

In order to further reduce the light loss of the light source, improve the distribution angle of the light to eliminate the problem of environmental pollution caused by the use of mercury. Replacing CCFL with LED as the backlight source of the device has become the development trend of static lighting LCD backlight source.

3. Feedback LED backlight

Using red, green and blue LEDs as LCD backlights can achieve excellent color quality, reduce power consumption, and avoid environmental pollution caused by the use of mercury. It is necessary to control the color temperature of white light to achieve a long enough life.

Recently, a feedback LCD backlight source has been developed that uses red, green and blue LEDs as the light source and adopts a color sensor and a feedback controller. With this backlight, color stability and sustained brightness stability of <0.02 have been achieved, and the white point and brightness of the device can be arbitrarily controlled.

Backlights can be divided into two categories: side backlights originate from bottom backlights. The side backlight is equipped with light-emitting strips around the light guide plate, and the light is diffused downward by the light guide plate; while the bottom backlight is a compact array of LEDs on the panel, and the diffuser plate makes it evenly divergent. It is mainly used in contour detection of measured objects, stain defect detection of transparent bodies, liquid crystal text inspection, size and shape inspection of small electronic components, bearing appearance and size inspection, semiconductor lead frame appearance and size inspection.

Light sources play a very important role in machine vision systems.

Features of the backlight:

1. The variety of colors is rich and varied

2. Long service life

3. Brightness diverges evenly

4. Customizable multi-color backlight for special occasions

When using the machine vision light source, pay attention to avoid using it in a high temperature environment, which will shorten its life in a high temperature environment; prevent aging and brightness reduction caused by self-heating.

Precautions for the use of machine vision light sources:

1. Use the light source with the lowest possible brightness level

2. A fan can be installed or air flow can be provided to dissipate heat and reduce the temperature to slow down the attenuation of brightness

3. You can only turn on the light source during imaging or use the strobe controller to match

Precautions for machine vision light source selection:

1. Understand the system structure and operation requirements, and determine the spatial structure relationship between the camera, the light source, and the measured object. The determined parameters are: field of view (FOV), working distance (WD)

2. The space structure includes: direct, side, and back.

The light source of the direct structure is a part of the ring light source, the coaxial light source, and the dome light source.

Light source of side-emitting structure - part of ring light source, strip light source, line light source, point light source

Back Illumination One - Square Backlight, Strip Backlight, Backlight Backlight.

3. For the observation and analysis of the object to be tested, dome light source should be used for curved surface detection, coaxial light source should be used for smooth surface, bright field light source should be used for rough surface, and infrared light source should be used for objects with good light transmittance. Identify what color is the back (what we don't need to detect) and what color is the foreground (what we want to detect).

4. A good light source can improve the contrast of the image - the background and the foreground are very clear, and the color of the foreground changes, and it is appropriate to use a colored light source or a white light source.