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Flat Lights for Machine Vision

Flat Lights for Machine Vision

This category of illumination contains highly homogeneous flat lights, typically used but not limited to backlighting. These highly diffuse LED backlights are often used to create silhouettes around components to generate robust black-on-white contrast. Square and rectangle flat LED vision lights manufactured by wenglor ensure excellent brightness for high contrasts.

Illumination Methods Using Flat Lights

Flat lights are most commonly used in one of these illumination methods.

Back Lights

By using flat lights as a common back light illumination, it is possible to create sharp silhouettes in applications such as pick-and-place. Additionally, this illumination method can be used for the inspection through clear parts.

Brightfield

By using flat lights as a direct illumination, it is possible to inspect very shiny surfaces. In the captured image, the surface appears as a mirror. If you place a flat light in the reflected field of view, it will reveal defects and marks of inspected areas.

LBB & ZVZF Flat Lights

Flat lights for Machine Vision lighting applications are available in three different back light sources: white light, red light and infrared light. These flat lamps create a homogeneous and diffuse light area in several different sizes – from small area LED flat lights to large area LED flat lights. This machinevision backlight solution creates high intensity illumination in any industry using image processing!

The depth of field depends on the lens aperture. The smaller the lens aperture, the larger the depth of field.
 
1) With more lighting power, …
2) … the aperture of the camera can be closed …
3) … which creates a bigger depth of field (DoF)!
In order to find the right size of the flat light, the relative position of the camera has to be taken into consideration. This position requires the vision light to be much larger than the size of the measured field of view.
 
1) Inspected field of view (FoV)
2) Required field of illumination

What Is the Parallax Effect?

Parallax is an effect experienced with industrial Machine Vision that relates to height as well as to how a light source is perceived by a camera. It appears when looking across an area from a single viewpoint.

The effects of the objects’ relative position to the camera are very important to understand in order to avoid parallax appearances. Common camera types use integrated calibration tools and telecentric lenses to correct this effect. With lighting, it can be adjusted with over-exposure in some instances.
 
1) Object 1 as captured with aperture f/8
2) Object 2 as captured with aperture f/8 creating the parallax effect
3) Object 2 as captured with aperture f/4 without the parallax effect

Which Effect Has the Inverse Square Law of Light?

The parallax effect as well causes a lack of homogeneity, which cannot be compensated. As light and distance follow the inverse square law of light, the back light for larger field of views require to be even brighter than small flat lights.
 
1) Objects directly under the camera: 100% brightness
2) Objects seen from a wider angle: less brightness

Which Working Distance Should Be Chosen?

We recommend to use a working distance (WD) of at least two times the largest diagonal (C) of the field of view (FoV).
 
WD > 2 × C
By controlling the exposure time and aperture to change the saturation in the image, different results can be achieved.
 
Left: Aperture f/4
Right: Aperture f/8

LBB Flat Lights

LBB flat lights are used to illuminate areas with a luminuous field starting from 200 × 200 mm. Because space is very limited in industrial environments, the LBB flat light comes with 4 mm borders, mounting points around the entire perimeter and a huge range of sizes.

ZVZF Flat Lights

ZVZF flat lights are used to illuminate small areas with a luminuous field starting from 60 × 60 mm. They have a rugged housing with protection class IP67. Due to their extremely thin housing of only 20 mm and small borders of only 4 mm, these vision lights are perfectly suited to fit in hard-to-access industrial environments with limited spaces.
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