Compact machine vision lighting for tight spaces

Lighting usually gets whatever space is left at the end of a machine design, and that space is rarely generous. The reflex is to hunt for the smallest fixture that fits and hope the image works out. The better order is the reverse: decide the lighting geometry the part needs, take the shallowest fixture that still delivers that geometry, then recover the brightness a compact fixture loses by strobing. This guide gives you the housing depths you can plan around for each fixture family, the duty-cycle arithmetic that turns a compact light into a bright one for the exposure only, a worked gauging example, and the cases where shrinking the light is the wrong answer.

Decide the geometry before you shop for a small box

A compact light with the wrong geometry fails the inspection no matter how neatly it fits. Contrast comes from where the light sits relative to the part's surface angles, not from fixture size. Classify the task first; the envelope comes second.

The first fork — surface reflection versus silhouette — is walked through in machine vision lighting angles: surface or silhouette?, and the guide to illumination types shows the optics behind each row. The lighting selection guide by inspection task is the fastest route from task name to geometry.

Dark field survives the tightest quarters, because the light only has to graze the surface at a shallow angle:

The shallowest fixture that keeps each geometry

Silhouette: flat backlights from 24 mm high

Depth behind the part is what silhouetting consumes, so depth is the number to attack. The LS-BKL-S04 series is 30 mm high and the LS-BKL-S06 series is 24 mm high, with an edge-lit ultra-thin type below that where the cavity is truly tight. The catalogue stocks them in the backlights category.

Size the lit area first: keep 10 % spare around the field for placement tolerance, so a 120 mm field needs 132 mm of lit length (120 × 1.1 = 132). Every later number hangs on the field of view, so settle it with the field of view and focal length calculator before the panel:

The LS-BKL-1468 is a 150 x 150 mm red flat backlight. That panel covers a field up to 136 mm square (150 ÷ 1.1 ≈ 136 mm). The LS-BKL-0750 is a 180 x 100 mm high luminance version for faster lines. For thick or bevelled parts a collimated panel keeps edge positions honest: the LS-BKL-0830 is a 120 x 120 mm collimated back light, and the trade-off against diffuse panels is worked through in collimated backlight or diffuse backlight for edge gauging.

Three flat panels that cover the common compact fields:

Directional contrast: slim bar lights

For print, texture and surface defects on a flat face, a slim bar set at 30–60° gives directional bright field in a profile that tucks beside the lens or between rollers. The LS-BAR-S03 series is 28.4 mm high and terminates in flying leads, so the envelope is bar height plus nothing. The bar lights category runs lit lengths from under 50 mm to well past a metre, with diffused and high-intensity types in the same slim profiles.

The LS-BAR-0484 is a 312 x 16 mm high uniformity bar light, and the LS-BAR-0400 is a 312 x 30 mm high luminance bar light for the shortest exposures. That 312 mm lit length covers a field up to 284 mm at the same margin (312 ÷ 1.1 ≈ 284 mm). Two of these bars opposed at a low angle are the compact dark-field array from the geometry table.

The classic slim pick for a directional small field:

Small fields and coaxial: spot lights

Where the feature is localised — a mark, a pin, a connector cavity — a spot beats a panel, because all of the output lands in a few tens of millimetres. The shallowest family in the catalogue is the LS-SPT-S07 series at 9.4 mm high, flying leads again. Beam angle sets the patch size: the LS-SPT-0024 pairs a 49.9 x 66.6 mm lit area and a 32° lens with a 455 nm blue output, and the LS-SPT-0037 covers a larger 99.9 x 141.6 mm patch through a 21° lens in cyan. For a coaxial set-up on a small shiny part, spot collector lights fold the output into the lens axis; the LS-SPT-0142 is a 94.2 x 24 mm, 3 W spot collector light. The spot lights category carries these in white, blue, red, green, infrared and ultraviolet.

Spots for the compact cases:

Depth is also wiring: the 24 V side

Nearly the whole catalogue runs on 24 V DC — 1,390 of the bar lights alone — so a compact station can share one supply with its sensors and trigger lines and keep the cabinet wiring thin. For the enclosure-side choices around that supply, the 24 V machine lighting guide for tight enclosures covers sizing and routing in cramped cabinets. Colour costs no depth: the same slim housings come in every wavelength family, and the contrast by LED colour guide picks the one the part needs.

Recover the lost brightness with a strobe

A compact fixture has fewer LEDs and a smaller lit aperture, so its continuous output per unit area drops. A triggered inspection does not need continuous light, though — it needs intensity during the exposure, and that is what a pulse buys:

Keep the average power at or below the continuous rating and the fixture never knows it is overdriven. At the duty cycles triggered inspection actually runs, that ceiling is far away. A 100 µs pulse at 10 parts per second is a duty cycle of 100 µs × 10 s⁻¹ = 0.001, or 0.1 %. Drive the peak at 10× the continuous current and the average is 10 × 0.1 % = 1 % — the light runs cooler than it would switched on all day.

As a rule of thumb, duty cycles under about 10 % leave room for several times the continuous drive as peak. The light's strobe rating at your exact pulse width is the binding figure, and 10× is the conservative design start. The overdrive, duty cycle and timing guide works the current side in detail, and the duty-cycle matching guide for lights and controllers covers the driver that has to deliver the peak.

A pulse is useless if it misses the exposure. Fire the light from the same trigger that gates the camera, and if the image comes back black, the strobe-timing fix for black images walks the fault end to end.

Worked example: silhouette gauging of a 100 mm part in a 40 mm gap at 500 mm/s

The case: a belt line gauges the edges of a 100 × 80 mm stamped part. The frame leaves a 40 mm gap under the belt for the light, and the camera fires once per part as each piece passes at 500 mm/s.

The inputs, and where each comes from:

• Part 100 × 80 mm (drawing); 10 mm clearance per side for placement tolerance (our standard margin) → field of view 120 × 100 mm.
• Smallest feature 0.5 mm (the burr to catch); blur budget a tenth of that, 0.05 mm (standard gauging practice).
• Belt speed 500 mm/s (line rate).
• Gap behind the part 40 mm (frame drawing).
• One trigger per part, 1 s⁻¹.

The rules, then the arithmetic:

1. Exposure cap. Blur = speed × exposure, so exposure ≤ blur ÷ speed = 0.05 mm ÷ 500 mm/s = 0.0001 s = 100 µs.
2. Coverage. Lit area ≥ field × 1.1 per axis: 120 × 1.1 = 132 mm, and 100 × 1.1 = 110 mm.
3. Depth. The 40 mm gap takes the 24 mm-high backlight class with 40 − 24 = 16 mm to spare, or the 30 mm class with 10 mm.
4. Duty cycle. D = 100 µs × 1 s⁻¹ = 0.0001, or 0.01 %. With the peak at 10× continuous, the average is 10 × 0.01 % = 0.1 % — thermal load is negligible.
5. Panel. The coverage target is 132 × 110 mm. The LS-BKL-1175 gives a 150 x 130 mm lit area, which clears the target. That leaves 18 mm of margin on the long axis and 20 mm on the short one.

Decision: a flat backlight in the 24–30 mm-high class with at least 132 × 110 mm of lit area, strobed 100 µs per trigger with the peak at up to 10× continuous. Continuous light cannot clear the 100 µs cap without a far bigger fixture; the pulse clears it with the compact one and adds almost no heat. If the gap shrinks below 24 mm, move to the edge-lit ultra-thin type rather than give up the silhouette.

When a compact light is the wrong answer

Shrinking works only while the geometry stays intact. Three cases where it does not:

• Curved or domed shiny parts need a dome or a large coaxial field, and those geometries need volume around the part — that volume is where their contrast comes from. A pocket-sized bar adds another highlight, not contrast. If the part says dome, grow the gap; the dome light guide shows how the part must sit inside the diffuse field.
• Heavy glare on flat reflective stock calls for crossed polarizers, which pass only a small fraction of the light. A compact fixture then needs the strobe from the last section to pay the brightness bill — the cross-polarization guide covers the set-up.
• Large fields punish distance. Intensity falls with the square of the stand-off, so moving a light from 50 mm to 300 mm costs (300 ÷ 50)² = 36× the output at the part. Beyond fields of roughly 200 mm, plan a larger fixture close in instead of a compact one pushed back; the large field of view lighting guide balances that trade in detail.

Fast line scan returns the same physics as line power rather than pulse duty, and the line scan light power guide sizes that case properly.

Checks before you order

Run this list before the purchase order:

• Measure the envelope at the light's own station, not the nearest open space: fixture depth + connector projection + cable bend. The flying-lead versions of the shallow families remove the connector from the stack.
• Size lit area at 1.1 × the field in both axes.
• Confirm the model pulses — a few backlights are constant-on only, which rules out every strobe trick above.
• Check the strobe rating at your pulse width, and pair the light with a strobe-capable controller; a plain 24 V rail will not deliver the peak.
• Budget heat as average power, peak × duty: at a 1 % duty a 10× strobe runs cooler than continuous, but bolt the light's back face to metal anyway.
• Pick colour for contrast last, not size first — the slim housings carry the same wavelength options as the big fixtures.

With geometry, depth, coverage and pulse numbers on paper, the light finder filters the catalogue by size, colour and type, and the configurator assembles the matched set:

If the gap resists every option above, the frame is the problem, not the catalogue — talk it through with us before the weld-up. The rest of the lighting material sits on the lighting topic page.