Machine Vision Light Source Selection: Point, Ring, Telecentric Parallel and Coaxial

POMEAS optical applications team · Reviewed by Tiger Xie · Published 2026-10-14

Quick answer. Machine vision light source selection is not about choosing the brightest lamp. It is about making the feature you must detect form a stable, repeatable grey-level difference against its background. Before deciding between a point light, a ring light, a telecentric parallel backlight or a coaxial light, fix six things first: the inspection target, the part material, how reflective the surface is, the part geometry, the camera field of view and working distance, and the line speed. Every POMEAS figure quoted in this article is taken from published product specifications; where a number is not published, this article gives you a measurement procedure instead of an estimate.

1. What the light source actually decides

In a machine vision system the camera receives the image, the lens transfers detail to the sensor, and the light source decides which features become visible at all. A complete imaging chain looks like this:

Light source illuminates the part → light is reflected, scattered or transmitted → lens collects the light → camera forms the image → software identifies or measures

If the optical contrast established at the first step is unstable, no amount of extra camera resolution, sharpening or threshold tuning will deliver a stable result over months of production. The same part, under a changed illumination direction or a different light source geometry, can turn a scratch from nearly invisible into a bright line, a character from low contrast into clean black and white, and an edge from a soft gradient into a defined boundary.

That is why the target and the illumination geometry have to be chosen together:

Inspection target	Image effect you want	Illumination approach to evaluate first
Outer profile and dimensions	Clean black-and-white boundary between part and background	Backlight, or telecentric parallel backlight
Flat characters and silkscreen	Clear grey-level difference between mark and substrate	Ring light, coaxial light, or a specific wavelength
Scratches, pits and burrs	Defect produces a highlight or a shadow	Low-angle illumination, directional point light, ring dark field
Flat reflective surface	Sound surface uniformly bright, defects dark or bright	Coaxial light
Small holes or local marks	Concentrated, high-contrast illumination over a small area	Point light or directional spot light
Large plain surface	Uniform brightness, minimal shadowing	Ring light, bar light or diffuse illumination

2. Decide reflected or transmitted before anything else

Before comparing light source types, separate the job into two families: are you inspecting the surface of the part, or its outline?

Reflected illumination

The light source and the camera sit on the same side of the part. Light reaches the part and is reflected or scattered back into the lens. Reflected illumination is normally used for:

character and silkscreen recognition;
scratches, stains and pits on a surface;
PCB, chip and electronic component surface inspection;
direct viewing of metal, plastic and glass surfaces.

Point lights, ring lights and coaxial lights are all reflected-illumination solutions.

Transmitted illumination

The light source is mounted behind the part and the camera and lens are on the opposite side. The part blocks the light and forms a silhouette. Transmitted illumination is normally used for:

outer diameter, inner diameter, length and pitch measurement;
through-hole, notch and edge detection;
gear, connector and precision hardware profile measurement;
outline inspection of transparent or translucent parts.

Telecentric parallel light is used as a collimated backlight. A normal diffuse backlight emits over a wide range of angles, so light diffracts and spreads around the part edge and the edge becomes a soft penumbra. A collimated backlight constrains the exit direction of the light, which reduces that penumbra and is the reason it is paired with telecentric lenses for dimensional work.

3. Point lights: concentrating light on a small area

A point light has a small emitting area and strong directionality, so the light can be concentrated onto a local region of the part. Its advantage is not coverage — it is the ability to generate highlights or shadows that reveal local height differences.

Inspection tasks that suit a point light

small holes, grooves and local structural features;
laser marking, characters and small marks;
small-area scratches, chipping and burrs;
cases where a shadow is used to judge local height change;
local fill lighting inside a microscope or small-field-of-view setup.

Where a point light stops working

Because the beam is directional, an unsuitable angle creates hard shadow, local overexposure or a specular return. For a large field of view, or for surface inspection that needs uniform brightness, a single point light is usually the wrong starting point; you either combine several point lights or move to a ring light, bar light or diffuse illumination.

POMEAS point and spot products in this family include the PMS-SL30-5V3W point light and the PMS-VP6025-08 compact 3 W spot light. The catalogue specification for the point light family lists models with a top diameter, an emitting-area diameter and a nominal power of 1 W or 3 W at 5 V, and the family is documented as usable on its own, with a microscope objective, or with a telecentric lens that has a coaxial port.

When tuning, change the source height, the incident angle and the azimuth independently, and watch whether the target feature becomes more distinct as the angle changes. Changing height alone often produces a change in spot size rather than a change in contrast.

4. Ring lights: multi-directional illumination around the lens axis

A ring light is mounted in front of the lens with LEDs arranged around the optical axis, so it illuminates the part from many directions at once and tends to suppress the hard shadow that a single directional source produces. It is one of the most widely used light source geometries in machine vision because it is easy to mount and works on many ordinary surfaces.

Inspection tasks that suit a ring light

character, label and 2D code reading;
PCB, connector and electronic component inspection;
surface viewing of metal, plastic and ceramic parts;
general scratch, stain and appearance defect inspection;
presence/absence, positioning and assembly-state checks.

High-angle and low-angle ring lights are not the same tool

A ring light does not have a single illumination effect; the working angle decides what it reveals.

High-angle ring light — the illumination direction is close to the lens axis. Suitable for characters, colour and ordinary flat surfaces.
Low-angle ring light — the light grazes the surface at a small angle. A flat region stays dark, while scratches, burrs, dents and raised features scatter light into the lens and appear as bright defects.

The published POMEAS ring light series (GH) spans 24 V models with LED ring counts from one to seven, nominal power from 0.4 W to 41.8 W, and outer diameters from roughly 25 mm to 350 mm across the range, with red, white and blue options on the standard part numbers. Peak wavelengths and colour temperatures are listed in section 9.

Where a ring light stops working

On highly reflective metal, glass or curved parts, an ordinary ring light can produce a ring-shaped bright band, central glare or irregular hot spots. The usual moves are:

change the distance between the ring light and the part;
change the incident angle;
reduce brightness and re-set exposure;
add a diffuser plate or a crossed polariser;
switch to coaxial light, a dome light, or another diffuse arrangement.

5. Telecentric parallel backlights: collimated transmission for edge definition

A telecentric parallel backlight collimates the light from its LED array so that the emitted beam stays as parallel as the optics allow. It is mounted behind the part and forms a transmitted-illumination system with the camera and lens. Compared with a normal backlight, the collimated output reduces the penumbra caused by diverging light, which makes the part edge sharper and is why this family is specified for profile and dimensional work.

The POMEAS catalogue states three application consequences for this family: it is designed specifically for backlighting, it raises the edge-profile contrast of the inspected part and removes the boundary effect, and it lets a telecentric lens realise its natural depth of field and telecentricity.

Inspection tasks that suit a telecentric parallel backlight

outer diameter, inner diameter and length measurement;
gear, cutting tool and precision hardware profile inspection;
hole diameter, pitch and notch measurement;
outer profile viewing of transparent parts;
telecentric-lens dimensional measurement systems;
backlight applications where edge smear and halo must be reduced.

Straight-through series: published specifications

The VP-GLTD series is the straight-through geometry, quoted with part numbers in the #901 series:

Model	Part no.	Beam diameter	Working distance	Outer diameter	Length	Forward voltage	Forward current	Colours
VP-GLTD-30R/G/B/W	#901-030	30 mm	45–90 mm	43.5 mm	121.16 mm	3.5 V	350 mA	R/G/B/W
VP-GLTD-60R/G/B/W	#901-060	60 mm	90–180 mm	72 mm	180 mm	3.5 V	350 mA	R/G/B/W
VP-GLTD-100R/G/B/W	#901-100	100 mm	150–300 mm	174 mm	276 mm	3.5 V	350 mA	R/G/B/W
VP-GLTD-145R/G/B/W	#901-145	145 mm	100–300 mm	162 mm	358 mm	3.5 V	350 mA	R/G/B/W
VP-GLTD-189R/G/B/W	#901-189	189 mm	250–500 mm	203 mm	472.6 mm	3.5 V	350 mA	R/G/B/W
VP-GLTD-265R/G/B/W	#901-265	265 mm	150–500 mm	275 mm	609 mm	3.5 V	350 mA	R/G/B/W

Corner-cut series: published specifications

A straight-through backlight requires coaxial stacking — camera, lens, part and backlight on one axis. When a frame or a conveyor occupies that position, a corner-cut backlight moves the emitting axis to the side and turns the beam through 90° with a mirror while keeping the emitting surface parallel to the part. The VP-GLTDL series is the corner-cut geometry, quoted with part numbers in the #902 series:

Model	Part no.	Beam diameter	Recommended working distance	Length	Forward voltage	Forward current	Colours
VP-GLTDL-30R/G/B/W	#902-030	35 mm	45–90 mm	121.16 mm	3.5 V	350 mA	R/G/B/W
VP-GLTDL-60R/G/B/W	#902-060	60 mm	90–180 mm	171.5 mm	3.5 V	350 mA	R/G/B/W
VP-GLTDL-100R/G/B/W	#902-100	100 mm	150–300 mm	235.5 mm	3.5 V	350 mA	R/G/B/W
VP-GLTDL-145R/G/B/W	#902-145	145 mm	100–300 mm	325 mm	3.5 V	350 mA	R/G/B/W
VP-GLTDL-189R/G/B/W	#902-189	189 mm	250–500 mm	356 mm	3.5 V	350 mA	R/G/B/W
VP-GLTDL-265R/G/B/W	#902-265	265 mm	150–500 mm	438.26 mm	3.5 V	350 mA	R/G/B/W

Two things are worth checking on the datasheet before you freeze a design. First, the headline on the series page describes the available aperture range, while the beam diameter is listed per model in the specification table — the two numbers are not the same quantity, and it is the beam diameter that has to cover your field of view. Second, the same nominal size does not always carry the same working-distance range between the straight-through and corner-cut series, so compare the row you actually intend to order rather than only the number in the model name.

A telecentric parallel backlight is not a substitute for a telecentric lens

This is the most common conflation in real selection work. A collimated backlight improves the direction of the backlight and the quality of the edge. It does not, on its own, remove the perspective error of an ordinary lens, and it does not keep the imaging magnification constant as the part moves through the depth of field. If the requirement is to reduce magnification error caused by part height variation, you still have to evaluate an object-side telecentric or a double-telecentric lens.

Operating limits to respect

operate within the working-distance range specified for the model;
the effective emitting aperture must cover the whole field of view plus a positioning allowance;
the part has to sit between the light source and the lens;
it is a profile and transmission tool — it is not the method for viewing front-side scratches, characters or surface texture;
final measurement accuracy still depends on the lens, the camera, the calibration and a repeatability test.

6. Coaxial lights: turning flat surfaces into a bright field

A coaxial light uses a half-mirror to inject light along a direction close to the camera optical axis. On a flat mirror-like or highly reflective surface, the sound area returns the light almost back along the incoming direction and reads as a uniform bright field; scratches, pits, characters and locally tilted regions change the return direction and appear as a break in that field.

Inspection tasks that suit a coaxial light

flat metal surface inspection;
PCB pads, chip and wafer surface viewing;
glass substrates and flat mirror-finish materials;
flat silkscreen, character and mark reading;
scratches, press marks, pits and coating defects;
print quality and packaging surface inspection.

The catalogue lists the coaxial light family as using a high-density LED array with a specially coated half-mirror, and documents four application groups: laser marking on wafers, engraved characters on metal surfaces, bearings and beverage cans, printed 2D codes on metal and glass substrates, and LCD panel defects.

Where a coaxial light stops working

A coaxial light is sensitive to surface angle. If the part is distinctly curved, inclined, or has a large height change, part of the return beam no longer reaches the lens and those regions read noticeably dark. For large curved areas, strongly reflective arc surfaces and complex 3D parts, a dome light or multi-directional diffuse illumination is usually the better answer.

There is also an optical cost: the beam splitter inside a coaxial unit discards part of the light. Allow for that when you compare brightness against an on-axis reflected solution, and confirm the margin against your exposure time and tact time rather than against a nominal brightness figure.

7. Comparing the four light source types

Type	Illumination character	Suited to	Not suited to	What to nail down at selection
Point light	Concentrated, directional, high local brightness	Small holes, local characters, grooves, small-area defects	Uniform inspection of a large surface	Incident angle, distance, spot size, shadow direction
Ring light	Multi-directional illumination around the lens, easy to mount	General surfaces, characters, positioning, ordinary defects	Complex highly reflective curved parts and specular glare	Working angle, inner/outer diameter, working distance, uniformity
Telecentric parallel backlight	Collimated transmitted illumination, small profile penumbra	Profiles, outer diameter, hole diameter, pitch, precision dimensions	Surface texture, characters, front-side scratches	Effective aperture, collimation, working distance, field coverage
Coaxial light	Light nearly collinear with the lens axis, contrast from specular return	Flat reflective surfaces, pads, chips, glass, flat characters	Distinctly curved or inclined surfaces and large height differences	Part flatness, beam-splitter aperture, brightness, working distance

8. Matching the light source to the inspection task

8.1 Outer profile and dimensional measurement

If the job is outer diameter, inner diameter, hole position, length, notch or profile, evaluate a transmitted backlight first. When accuracy requirements are higher, when the part has some height, or when you want to reduce profile penumbra, move to a telecentric parallel backlight and pair it with a telecentric lens.

8.2 Flat reflective surfaces

For flat metal, PCB pads, chips and glass planes, evaluate coaxial light first. It makes the sound plane a relatively uniform bright field, while scratches, pits and locally tilted regions form contrast because their return direction changes.

8.3 Ordinary surfaces, characters and positioning

For parts that are not strongly reflective and are reasonably flat, a ring light is usually the easiest first test. You still have to tune height, angle and brightness against the actual part — clamping a ring light in front of the lens is not a completed selection.

8.4 Small holes, grooves and local features

If the region of interest is small and you want directional illumination to reveal local height difference, consider a point light. Aim for a highlight or a shadow from a specific direction, and avoid an angle that occludes the target or puts a direct specular return into the lens.

8.5 Curved and complex highly reflective parts

Point, ring and coaxial lights will not solve every reflection problem. For curved metal parts, plastic housings, packaging film and complex curved surfaces, you may need a dome light, a bar light, a multi-directional combination, or a polarisation scheme to obtain a more uniform surface illumination.

9. Parameters to confirm before ordering

9.1 Light source size against field of view

The effective illuminated area has to cover the camera field of view, plus part positioning variation and mounting allowance. If the effective emitting area is smaller than the field of view, brightness can fall off at the image edge and the software can flag the grey-level difference between different positions as a false defect. A practical rule is to size the emitting area so that the uniformly illuminated region — not the mechanical outer diameter — covers the field with an allowance for positioning.

9.2 Working distance

The same light source behaves differently at different working distances: brightness, coverage and incident angle all change. This matters most for point lights, ring lights and coaxial lights, where the mounting position has to be fixed against the lens working distance and the available space inside the machine.

9.3 Colour and wavelength

White light suits general viewing and colour cameras. Red, blue, green and infrared exploit the difference in reflection and absorption between materials to raise contrast between target and background. Colour cannot be chosen from appearance alone — test it on the real part. The published POMEAS wavelength set across the light source families is:

Colour	Peak wavelength or colour temperature
Red	620–630 nm, and 645–660 nm
Green	525 nm
Blue	470 nm
White	6500 K (colour temperature)
Infrared	850–950 nm
Ultraviolet	365 / 395 nm

9.4 Brightness, exposure and gain

Source brightness has to be adjusted together with camera exposure time, lens aperture and camera gain. When the light is short, raising gain alone adds noise, and lengthening the exposure can introduce motion blur. For fast-moving parts, raising the instantaneous intensity and shortening the exposure — and evaluating strobe control — is the better direction.

9.5 Continuous or strobe illumination

Static or slow projects can use continuous illumination. High-speed conveyors, rotary tables and flying-shot projects may need a strobe controller synchronised to the camera's hardware trigger. A strobe source also has to be confirmed for peak current, pulse width, trigger delay, thermal behaviour and permitted duty cycle.

9.6 Polarisation

For strong reflection from metal, glass, plastic film and coated surfaces, a crossed polariser in front of the source and the lens can suppress part of the specular return. A polariser costs brightness, so source power, exposure time and aperture all have to be re-tuned after you add it.

9.7 Uniformity and stability

Dimensional measurement and grey-level analysis projects need more than average brightness: they need the brightness across the whole field of view to be uniform, and to stay stable over a long run. Source temperature rise, LED ageing, controller variation and ambient light change can all move the result. The published adaptation and environment figures for the POMEAS light source families are:

Item	Published specification
Controller	VP-DPI2404-4-RS232T (catalogue); RS-232 controllers GE5-4PRT and PMS-DC5V3W-4T also published on site
Operating environment	0–40 °C; 20–85 %RH, non-condensing
Adaptation	Diffuser plate (standard on some models); extension cable 1 / 3 / 5 m (optional; 0.5 m standard)
Expected service life	At 25 °C ambient, white light at 50 % brightness runs continuously and reliably for more than 30,000 h (50 % decay criterion)
Customisation	Part features, working distance, incident angle, colour and field of view can be customised on request

10. Common light source selection mistakes

Chasing brightness without considering illumination direction.
Measuring a profile dimension while using only front-side reflected illumination.
Inspecting a surface scratch while illuminating the surface too uniformly.
Assuming a ring light solves every surface inspection problem.
Using a telecentric parallel backlight as if it were ordinary front-side illumination.
Assuming a coaxial light removes all reflection problems.
Ignoring the match between light source size and camera field of view.
Not confirming whether the part surface is flat, curved, or changes height.
Testing only with the machine stopped, without validating the real line speed.
Compensating for inadequate light by permanently raising camera gain.
Not comparing candidate light source options on raw images.
Ignoring ambient light, temperature rise and long-run stability.

11. An eight-step light source selection procedure

Step 1 — Define the inspection target

Decide whether the job is a surface defect, a character, a colour, a profile, a dimension, a hole position or an assembly state. "See the part clearly" and "reliably identify one specific feature" are different objectives, and the source has to be designed around the feature you must actually identify.

Step 2 — Establish material and reflectivity

Confirm whether the part is metal, plastic, glass, ceramic, PCB, transparent or a composite, and whether the surface is mirror-like, semi-reflective or diffuse.

Step 3 — Establish part geometry

Decide whether the region of interest is flat, curved, inclined, a groove, a raised feature or a profile edge. The same material reflects in completely different directions once the geometry changes.

Step 4 — Choose reflected or transmitted

Surface features usually need reflected illumination; profile and dimensional work usually starts with a transmitted backlight.

Step 5 — Fix the illumination direction

Decide whether you need front, high-angle, low-angle, side, coaxial or back illumination. In many projects, changing the direction is more effective than raising the brightness.

Step 6 — Select the light source type

Use the earlier decisions to choose a point light, a ring light, a telecentric parallel backlight or a coaxial light, or to go further into bar lights, dome lights, area lights and combined illumination.

Step 7 — Validate exposure and tact time

At the real production speed, check exposure time, image brightness, gain, frame rate and motion blur. High-speed projects also have to confirm that strobe triggering and camera acquisition are synchronised.

Step 8 — Compare on real samples

Use known-good, known-bad and marginal samples, and compare raw images across source types, angles, colours and brightness levels. Do not judge on whether the picture looks attractive: check the grey-level difference of the target feature, edge stability, repeated inspection results and false-call behaviour.

12. Worked judgement examples

Gear outer diameter and tooth profile

Evaluate a telecentric parallel backlight as the collimated source so the gear forms a clean silhouette. If accuracy requirements are higher, pair it with a telecentric lens of the appropriate magnification and carry out calibration and a repeatability test.

Laser characters on a flat metal surface

Evaluate coaxial light first so the flat metal reads as a relatively uniform brightness and the character region forms contrast through a difference in reflectivity or surface structure. If the return is still too strong, test a crossed polariser or a different wavelength.

Small holes and local laser marking

Use a point light from a specific direction so the hole edge, the marking or the depression produces a highlight and a shadow. Iterate across several angles to avoid too small a spot or a direct specular return into the lens.

PCB and electronic component surfaces

For ordinary component positioning, test a ring light first. To view flat pads, chip surfaces or highly reflective areas, evaluate coaxial light. Real projects sometimes need the ring light and the coaxial light triggered in sequence to present different feature types.

13. When these four types are not enough

Long, large-area parts may suit a bar light better. The published bar light series covers lengths from a few tens of millimetres to several metres, allows the illumination angle to be adjusted, and several bar lights can be combined.
Complex curved surfaces and highly reflective arc surfaces may need a dome light. The POMEAS dome light series is a diffuse shadowless source with models across a range of diameters, intended for surfaces that are uneven or reflective.
Internal defects in transparent parts may need a specific wavelength or multi-angle illumination.
Very-low-angle scratch detection may need a ring dark field or a linear dark-field source.
A large uniform backlight may need a flat area light rather than a telecentric parallel backlight. The published parallel-flat series is listed from 0.8 W to 29 W at 24 V across a range of square sizes, and the manufacturer states that its booster plate raises source brightness by 20 % to 50 % compared with other comparable sources on the market — a manufacturer's figure rather than an independently verified one.
High-speed moving inspection may need a dedicated high-intensity strobe source and controller.
Simultaneous surface and profile inspection may need several light groups triggered in sequence.

There is rarely a single light source that covers every feature. Complex projects normally acquire images under separate illumination conditions and let the software combine the judgements. A shadowless ring light series, an ultraviolet family covering ring, bar, area, coaxial and point formats at 365 / 395 nm, and an infrared family at 850 / 950 nm are also published for cases where the geometry or the material rules out visible broadband light.

14. What to send for a lighting evaluation

To select a light source with reasonable confidence, the following inputs help most:

An original image of the part and its dimensional drawing.
The exact position to be inspected.
The defect or feature type.
The smallest defect size that must be identified.
Part material, colour and degree of reflectivity.
Whether the surface is flat, curved or has raised/recessed structure.
Camera model, resolution, and monochrome or colour.
Lens model, focal length or magnification.
Horizontal and vertical field of view.
Working distance.
Whether the part moves, and at what speed.
Permitted exposure time and tact time.
The light source currently in use and its mounting position.
A raw image from the current setup.
The installation space available inside the machine.
Whether strobe, polarisation or a specific wavelength is required.

The more complete the input, the easier it is to tell whether the problem comes from the source type, the illumination direction, the brightness, the wavelength, or from the camera and lens themselves.

Frequently Asked Questions

Is a brighter machine vision light source always better?

No. Excessive brightness causes local overexposure, glare and loss of detail. What matters more in selection is illumination direction, uniformity and the contrast of the target feature. Brightness should be tuned together with aperture, exposure time and camera gain.

How do I choose between a ring light and a coaxial light?

A ring light suits most ordinary surfaces, characters and positioning work, and is relatively easy to mount and adjust. A coaxial light is better for flat, highly reflective surfaces, where it produces a uniform bright field through the on-axis specular return. Distinctly curved or inclined surfaces are usually not a good fit for coaxial light alone.

Can a telecentric parallel backlight replace a telecentric lens?

No. A telecentric parallel backlight provides collimated backlighting and improves the profile edge by reducing penumbra. Reducing perspective error, and the magnification change caused by part height variation, still requires a telecentric lens together with a complete calibration and measurement chain.

What is the difference between a diffuse backlight and a telecentric parallel backlight?

A diffuse backlight emits over a wide angular range from every point on the emitting surface; a telecentric parallel backlight constrains the exit direction close to the surface normal. The collimated version reduces the penumbra at the part edge, which is why it is specified with telecentric lenses, particularly at higher magnification. Both are mounted behind the part and both produce a silhouette; the difference is the angular distribution of the emitted light, not the mechanical arrangement.

Why is a stationary image sharp but the same part blurry when the line is running?

The usual causes are an exposure time that is too long, a part moving too fast, or machine vibration. Raise the instantaneous light intensity, shorten the exposure, and check that strobe triggering and camera acquisition are synchronised.

How do I choose between white, red and blue light?

White light suits general viewing and colour imaging. Monochromatic wavelengths such as red and blue exploit the difference in how a material reflects and absorbs different wavelengths, which can raise contrast, and they also make it easier to add a matching filter that rejects ambient light. Confirm the choice on a real sample rather than from a colour chart.

Can one machine vision system use several light sources?

Yes. Complex projects frequently trigger a ring light, a coaxial light, a backlight or other sources in sequence to acquire surface, character and profile images separately. The camera trigger, controller timing, exposure time and software processing time all have to be confirmed together.

How do I confirm that a light source selection is actually correct?

Test with known-good, known-bad and marginal samples, at the real working distance, camera settings and production speed. Beyond whether the image looks sharp, compare the grey-level difference between target and background, the uniformity across different positions, the repeated inspection result, and stability over a long run.

Does the working distance of a ring light change its brightness?

Yes. On a ring light, moving the source further from the part changes both the illuminated area and the effective incident angle, so brightness and the character of the shadowing change together. That is why the mounting position has to be fixed against the lens working distance and then tuned on the real part, rather than set once at a nominal figure.

Which light source family should I look at for a large, long part?

A bar light is usually the better starting point for large, long parts, because several units can be combined and the illumination angle can be adjusted. For a large area that needs uniform backlighting, a flat area light is more appropriate than a telecentric parallel backlight, which is designed around a defined beam diameter for profile work.

Talk to a POMEAS Engineer About Your Lighting Setup

If the part is in front of you and the image is not yet doing what you need, send the part image, the current capture, the camera or lens model, the region you need to inspect and the line speed. We can start from the illumination direction rather than from a product name.

Email: [email protected] | WhatsApp: +86 185 9810 2007

Please include: part material and surface condition, required field of view in mm, smallest defect in µm, working distance, available mounting space, whether strobe or polarisation is required, and the permitted exposure time at production speed.

Reviewed by Tiger Xie.

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