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LED Illumination for Machine Vision

On this page, you will find a comprehensive product guide on LED lighting for machine vision, as well as a wide range of manufacturer-independent products. This allows you to benefit from one of the most comprehensive lighting portfolios in Europe and directly compare and select suitable solutions.

 

LED illuminations have become the universal standard for imaging applications. They offer an excellent price/performance ratio, unbeatable reliability and almost maintenance-free operation. They can be assembled in almost any shape and are available in many different colours (red, white, blue, green, IR, UV).

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When is LED lighting the optimal solution for your image processing needs?

LED lighting is now the most widely used light source in industrial image processing because it produces stable, targeted and reproducible lighting conditions, which are a basic requirement for achieving reliable results. It is particularly suitable for applications where specific features need to be made visible, such as edges, colours, surface textures or fine defects. Selecting the appropriate lighting techniques, such as incident light, transmitted light or dark-field lighting, enables even challenging materials or complex geometries to be clearly captured.
 

Unlike other types of lighting, LEDs offer a high degree of flexibility, with different designs for tight or large installation spaces, various wavelengths for optimised contrast and the ability to control light direction, intensity and colour precisely. This makes them the first choice for inspections, quality control, measurement tasks and high-speed processes, wherever reproducible image data and controlled light guidance are crucial.

Questions about LED lighting? We’d be happy to advise you!

Not sure which lighting is best suited to your needs? We can help with selection and integration, providing a quick, independent and practical service.

 

More than just LED lighting - we support your entire machine vision project.

 

From selecting the lighting and conducting tests to system integration, we support you through every phase of the project, ensuring that your image processing is reliable, stable and precisely tailored to your requirements.

 

Red ring light Machine Vision Illumination Red ring light Machine Vision Illumination

Selecting LED lighting by application (product guide) 

In industrial machine vision, the right lighting systems are crucial for achieving optimal contrast, process stability and, ultimately, image quality. However, given the wide variety of lighting techniques, designs and wavelengths, the following question quickly arises: Which LED lighting is best suited to my machine vision application?
 

This product guide will help you find the right solution, from choosing the lighting technology (incident light, transmitted light or dark field) and the optimal design, to selecting the appropriate spectrum. It also shows you how to use the STEMMER IMAGING Product Finder to narrow down your selection in just a few steps, even without prior knowledge.

1. Which LED lighting technique provides the right contrast? (incident light, transmitted light, dark field)

The illumination technique you choose determines the level of contrast you can achieve. This is why it is the most important step when selecting LED lighting. Each technique produces a different image of the scene and thus offers different possibilities for analysis.


Incident light – the standard solution for structures, colours & markings

With incident light, the object is illuminated from the front. This clearly highlights surface features, printed images, colours and codes. Depending on the light distribution (diffuse, coaxial, focused), reflections can be suppressed or utilised in a targeted manner.


Ideal for: print inspection, colour inspection, barcode and data matrix recognition, structure inspection.


The appropriate illumination geometry, such as ring, spot or flood lighting, can easily be adapted to the size and surface of your component during the selection process.


Backlight – maximum contrast for edges & silhouettes

Backlighting produces a high-contrast light-dark image because the object appears as a dark silhouette against a homogeneous background. Perfect for tasks where the external shape is crucial.


Ideal for: contour analysis, measurement, presence detection, transparent or semi-transparent materials.


Backlights provide very uniform illumination for silhouette and edge-based tasks. Linear backlights can also be used for moving web inspection with line-scan cameras – important for precise measurement tasks.


Dark-field – visible micro-defects on glossy surfaces

With dark-field illumination, light strikes the object at a shallow angle. As a result, scratches, burrs, grooves, dust particles or engravings appear as bright lines or dots, whilst the rest of the surface remains dark.

Ideal for: metal, glass, films, polished or reflective surfaces.

Segmented designs or ring-shaped dark-field lights also enable highly targeted defect detection.


Typical decision criteria:
•    Inspecting surfaces, colours or markings? →Incident light
•    Evaluating edges, shapes or silhouettes? → Transmitted light
•    Detect the finest defects on shiny materials? → Dark-field
•    Not sure where to start? → Compare reflected light & transmitted light, supplement with dark field if necessary

2. Which LED design is best for your application?

The design determines how LEDs project their light onto the object – diffusely, focused, segmented or over a wide area.
Criteria such as beam angle, homogeneity, space requirements and light guidance, which can be combined in many configurations, help with the selection.

LED ring lights

Ring lights use several LED segments that emit light all round.
They provide uniform, low-shadow illumination, particularly with diffuse covers or segmented control.
Typical features:
•    variable light direction thanks to individually switchable LED sectors
•    Good control of reflections on metal and plastic
•    Available in a range of diameters – to suit camera distance and field of view

 

LED bar and line lights

Linear LED arrays produce a focused or diffuse line of light, often used for line-scan, web inspection, edge illumination, or linear backlighting.

Typical features:
•    High intensity thanks to tightly focused optics
•    perfect for web materials, edges or microstructural defects
•    Available in various lengths and power ratings

 

LED panel lights

Panels consist of numerous LEDs behind diffusers and produce an extremely homogeneous illuminated surface.
Typical features:
•    ideal for transmitted light (sharp-edged silhouettes)
•    Absolutely uniform illumination of large test areas
•    Optionally available with various diffuser and intensity levels

 

LED spotlights

Spots concentrate LED light using lenses or collimators.
Typical features:
•    Very intense light spot with high contrast
•    suitable for oblique lighting, narrowly defined areas or robotic applications
•    flexibly adjustable beam angle (optical variants)

 

LED dome lighting

Dome lights create a diffuse light chamber, powered by LEDs arranged in a ring.
Typical features:
•    Low-reflection rendering of glossy surfaces
•    Stable performance with uneven, curved or textured parts
•    Uniform 360° ambient light

 

Coaxial LED lights

LEDs are introduced into the optical path via beam splitters, creating a flat, shadow-free bright-field effect.
Typical features:
•    Ideal for reflective, flat surfaces
•    no lateral shadows or stray reflections
•    very stable with fine structures and markings


Practical tip:

The best design is achieved by considering three factors:
•    How big is the object? → determines light size & geometry
•    What effect should the light have? → diffuse, focused, segmented, flat
•    How much space is available? → determines whether to use a panel, ring light or spot

3. Which LED wavelength produces the best image contrast? (UV, VIS, IR, SWIR)

The wavelength influences which material properties become visible and how strongly structures, colours or defects stand out. Different spectra produce different image effects – important for stable, reproducible inspection.


White light (VIS, 400–700 nm)

Suitable for applications where multiple colours or different materials are assessed simultaneously.
Contrast behaviour:
•    natural representation of coloured surfaces
•    good overall differentiation with mixed materials
•    suitable for colour camera sensors


When is it useful?
When colour information is required or the scene needs to be assessed without strong spectral emphasis.

 

Monochromatic colours (red, blue, green)

Narrow-band light specifically enhances certain contrasts, as only one spectral range is used.Contrast behaviour:
•    can improve contrast and apparent sharpness by reducing chromatic aberration effects
•    emphasize wavelength-dependent reflectance
•    clear colour contrasts (e.g. blue brings out yellow tones particularly well)


When is this useful?
When markings, edges, printed images or laser engravings need to be emphasised

 

UV (365–400 nm)

UV light activates fluorescence and makes fine details visible that are barely discernible in the visible spectrum.
Effects:
•    Revealing adhesive residues, coatings, micro-cracks
•    Highlighting of fluorescent materials
•    High level of detail in fine structures


When is this useful?
When surfaces are required to react or fluoresce, or when very fine defects need to be detected.


IR / NIR (700–1000 nm)

Infrared reduces visible colours and minimises the influence of colour information.
Contrast behaviour:
•    reflection behaviour can differ from the visible range, but still depends strongly on material, surface roughness, angle of incidence and polarisation
•    Penetration of certain materials (e.g. labels, thin films)
•    Stable in changing ambient light


When is it useful?
When colour or print information is undesirable or reflections interfere with evaluation.

 

SWIR (1000–1700 nm)

Reveals material properties that remain hidden in visible light.
Effects:
•    Detection of moisture, fill levels, differences in density and layers
•    Analysis of internal structures
•    Can be combined with suitable sensors and filters to reduce the influence of visible ambient light


When is it useful?
For demanding inspections in food, pharmaceutical, electronics or packaging applications.


Tip:

The most reliable way to determine the correct wavelength is to ask three questions:
•    Which feature needs to be visible? (Colour, structure, coating, defects)
•    Do reflections play a role? ((IR may reduce the influence of visible colour, while UV can reveal fluorescent responses)
•    What type of camera is being used? (Monochrome cameras are often preferred for maximum sensitivity and contrast, including with narrow-band light, while colour cameras are used when true colour information matters)

4. Continuous light or LED strobe? – The right operating mode for your speed

The choice of operating mode affects how stable moving or static scenes are captured. While continuous lighting provides constant illumination, strobe lighting enables extremely short, bright flashes – ideal for fast-moving action or short exposure times.


Continuous Lighting

The lighting remains on continuously at an adjustable intensity.
Suitable for applications without extreme movement or where continuous evaluation is required.
Contrast behaviour and effects:
•    Constant brightness for stationary or slowly moving objects
•    Ideal for setups with a fixed exposure window
•    Stable when used with line scan cameras or continuous inspection stations


When is it appropriate?
When the speed is moderate or the system requires continuous illumination (e.g. for ongoing process monitoring).

 

Strobe / Flash mode

In flash mode, short, very bright light pulses are generated that are perfectly synchronised with the camera exposure.
Effects:
•    High light output in an extremely short time
•    ‘Freezing’ of fast movements due to reduced motion blur
•    significant intensity reserves at very short exposure times


When is this useful?

For fast conveyor belts, rotating parts, pick-and-place movements, or when high contrast is required despite short exposure times.
Synchronisation & control
Flash operation requires precise synchronisation between the lighting and the camera.
Modern lighting modules are often equipped with integrated electronics that:
•    Precisely controls pulse duration
•    In some cases support short overdrive or peak-mode pulses within specified duty-cycle limits
•    Can process trigger signals directly from the camera
These functions help you to identify lighting systems that can be synchronised cleanly during the selection process.

 

Practical tip:

The operating mode is usually determined by three factors:
•    Subject movement: fast → strobe; slow/static → continuous light
•    Exposure time required: very short → strobe
•    Available intensity: high reserves required? → Strobe with peak capability


Strobe is particularly worthwhile when movement and short exposures would produce insufficient contrast.

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