SummaryThis level of in-depth analysis can and often does result in seemingly contradictory directions, and a compromise is necessary. For example, detailed sample/light interaction analysis might point to the use of the dark field lighting technique, but the inspection environment analysis indicates that the light must be remote from the part. In this instance, a more intense linear bar light(s) oriented in dark field configuration may create the contrast you want, but perhaps require more image post-processing. No matter the level of analysis, and understanding, there is quite often no substitute for actually testing the two or three light types and techniques first on the bench, then in actual floor implementation whenever possible. And when designing the vision inspection and parts handling/presentation from scratch, it is best to get the lighting solution in place first, then build the remainder of the inspection around the lighting requirements. The objective of this detailed analysis and application of what might be termed a “tool box” of lighting types, techniques, tips, and tricks is to help you arrive at an optimal lighting solution that takes into account and balances issues of ergonomics, cost, efficiency, and consistent application. This helps you to better direct your time, effort, and resources—items better used in other critical aspects of vision system design, testing, and implementation.

Illumination techniquesIllumination techniques comprise back lighting, diffuse (also known as full bright field) lighting, bright field (actually partial bright field or directional) lighting, and dark field lighting. The application of some techniques requires a specific light and geometry, or relative placement of the camera, sample, and light—others do not. For example, a standard bright field bar light may also be used in dark-field mode; whereas a diffuse light is used exclusively as such. Most manufacturers of vision lighting products also offer lights with various combinations of techniques available in the same light, and at least in the case of LED-based varieties, each of the techniques may be individually addressable. This circumstance allows for greater flexibility and also reduces potential costs when many different inspections can be accomplished in a single station rather than two. If the application conditions and limitations of each of these lighting techniques, as well as the intricacies of the inspection environment and sample/light interactions are well understood, it is possible to develop an effective lighting solution that meets the three acceptance criteria.

Illumination of light formula

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According to the statement, the researchers made use of “transition metal perovskite materials” in the study. Using pulsed laser deposition—which involves a powerful pulse laser beam in a vacuum chamber—the researchers grew a 100-nanometer-thick membrane made of an oxide of strontium and titanium called strontium titanate (SrTiO3). Once completed with very few flaws, the films were removed from that substrate and placed on a silicon substrate.

SOURCES -- Practical Guide to Machine Vision Lighting.-- A Practical Guide to Machine Vision Lighting - National Instruments, 24 May 2019, www.ni.com/en-us/innovations/white-papers/12/a-practical-guide-to-machine-vision-lighting.html.

Illumination lighting meaning

To understand what happened next requires a brief foray into Particle Physics 101. Photons are particles of light and the fundamental unit of the electromagnetic spectrum. Phonons, on the other hand, are “a fancy word for a particle of heat” (according to MIT), but can also be thought of as sound energy. Both photons and phonons deal in the realm of excitations and vibrations—however, when an infrared photon is coupled with an optical phonon (a.k.a. a phonon that can emit or absorb light), then it forms a quasi-particle called a “phonon polariton.” It’s these polaritons that do the squeezing.

“We’ve demonstrated that we can confine infrared light to 10% of its wavelength while maintaining its frequency—meaning that the amount of time that it takes for a wavelength to cycle is the same, but the distance between the peaks of the wave is much closer together,” Yin Liu, a co-author of the study, said in a press statement. “Bulk crystal techniques confine infrared light to around 97% of its wavelength.”

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Types of illumination PDF

Dark Field LightingDark field lighting is perhaps the least well understood of all the techniques, although you do use these techniques in everyday life. For example, the use of automobile headlights relies on light incident at low angles on the road surface, reflecting back from the small surface imperfections, and also nearby objects. Dark field lighting can be subdivided into circular and linear, or directional types, the former requiring a specific light head geometry design. This type of lighting is characterized by low or medium angle of light incidence, typically requiring close proximity, particularly for the circular light head varieties (Figure 19).

The human eye is a natural wonder, the result of millions of years of evolutionary tinkering, and... remarkably limiting. Our eyes can only see a small sliver of the electromagnetic spectrum, so to see anything else requires relying on technology that can glimpse these “invisible” wavelengths.

Types of illumination in slit lamp

Back LightingBack lighting generates instant contrast as it creates dark silhouettes against a bright background (Figure 16). The most common uses are for detecting the presence/absence of holes and gaps, part placing or orientating, or measuring objects. Often it is useful to use a monochrome light, such as red, green, or blue, with light control polarization if precise (subpixel) edge detection becomes necessary.

What is illumination in the Bible

Application FieldsFigure 22 illustrates potential application fields for the different lighting techniques based on the two most prevalent gross surface characteristics: (1) surface flatness and texture and (2) surface reflectivity. This diagram plots surface reflectivity, divided into three categories—matte, mirror, and mixed—versus surface flatness and texture or topography. As you move right and downward on the diagram, more specialized lighting geometries and structured lighting types are necessary. As might be expected, the Geometry Independent Area implies that relatively flat and diffuse surfaces do not require specific lighting, but rather any light technique may be effective, provided it meets all the other criteria necessary, such as working distance, access, brightness, and projected pattern.

Light illumination level

Figure 22. Lighting Technique Application Fields: Surface Shape Versus Surface Reflectivity Detail (Although not shown, any light technique is generally effective in the Geometry Independent Area of the diagram.)

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General illumination

Partial Bright Field or Directional LightingPartial bright field lighting is the most commonly used vision lighting technique, and is the most familiar lighting used every day, including sunlight. This type of lighting is distinguished from full bright field in that it is directional, typically from a point source and, because of its directional nature, it is a good choice for generating contrast and enhancing topographic detail. It is much less effective, however when used on-axis with specular surfaces, generating the familiar “hotspot” reflection.

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Liu and his colleagues said that this breakthrough could lead to a whole new generation of infrared imaging technologies and thermal management devices. “Imagine,” Liu said, “being able to design computer chips that could use these materials to shed heat by converting it into infrared light.”

Illumination lighting design

Effective application of dark field lighting relies on the fact that much of the light incident on a mirrored surface that would otherwise flood the scene as a hotspot glare, is reflected away from rather than toward the camera. The relatively small amount of light that is reflected back into the camera is what happened to catch an edge of a small feature on the surface, satisfying the “angle of reflection equals the angle of incidence” equation (see Figure 21 for another example).

One of the most useful of these wavelengths is infrared, the waves of which stretches between 760 nanometers to 100,000 nanometers (the name comes from the fact that it’s just longer than the color red, the longest wavelength in the visible spectrum). Infrared is used in all sorts of applications—especially imaging—and being able to manipulate this wavelength can produce better results.

“Theoretical papers proposed the idea that transition metal perovskite oxide membranes would allow phonon polaritons to confine infrared light,” Liu said. “And our work now demonstrates that the phonon polaritons do confine the photons, and also keep the photons from extending beyond the surface of the material.”

To test this new device and see if it could “squeeze” infrared light to a useful degree—an idea that had insofar only been theoretical, according to the researchers—the team turned to the Advanced Light Source at the Lawrence Berkeley National Laboratory. This research facility runs an infrared program capable of probing materials at micro- and nano-scales. The team performed synchrotron near-field spectroscopy on the thin strontium titanate film, and what was once theoretical became very much practical.

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That’s why scientists from North Carolina State University worked to successfully “squeeze” infrared light to 10 percent of its wavelength while maintaining its frequency. The researchers achieved this breakthrough by using a special class of oxide membranes rather than bulk crystals, which can traditionally only barely squeeze infrared light. The results of this study were published earlier this month in the journal Nature Communications.

Diffuse (Full Bright Field) LightingDiffuse, or full bright field lighting, is most commonly used on shiny specular or mixed reflectivity samples where even but multidirectional light is needed. Several implementations of diffuse lighting are generally available, but there are three primary types (Figures 17a–c), with hemispherical dome/cylinder or on-axis being the most common. Diffuse dome lights are effective at lighting curved, specular surfaces, commonly found in the automotive industry, for example. On-axis lights work in a similar fashion for flat samples and are particularly effective at enhancing differentially angled, textured, or topographic features on relatively flat objects. To be effective, diffuse lights, particularly dome varieties, require close proximity to the sample. A useful property of axial diffuse lighting is that in this case, rather than rejecting or avoiding specular glare, you may actually take advantage of the glare if it can be isolated specifically to uniquely define the feature(s) of interest required for a consistent and robust inspection.

The following figures illustrate the differences in implementation and result of circular directional (partial bright field) and circular dark field lights on a mirrored surface.