Two heads that draw the same power can differ by several times in brightness at the part, and the reason is bolted to the front of the LEDs: the molded lens or diffuser that shapes the beam. Beam shaping is the first lighting decision, because it sets footprint, peak intensity and glare before you choose an angle to the part or a wavelength. This page gives the arithmetic behind that choice: compute any lens angle's footprint at any working distance, estimate how much intensity a tighter cone buys, and commit to focused or diffused based on the surface in front of the camera.
What the lens on a light actually does
A bare high-current LED sprays light across a hemisphere. The optic in front of it sets the full beam angle θ — the cone that carries most of the flux. A clear lens folds that spray into a narrow, direct beam, the brightest on-axis illumination the head can deliver. A frosted lens or diffuser window scatters the cone into a wide, soft envelope with a much lower peak.
Machine-vision ranges split on exactly this choice: bar lights come in standard and diffused types, and the spot lights print the lens angle in each model's data, 21° and 32° among them. Where the light sits relative to the part is a separate decision — the illumination types guide covers geometry. This page is about what the head's own optics do first, because geometry only pays off once photons actually reach the field of view.
Footprint: the number the beam angle sets
At a working distance WD, a lens of full beam angle θ lights a disc of roughly:
Beam-angle ratings mark the main cone; intensity rolls off toward its edge, so size the footprint about 30-50% larger than the field of view.
| Beam angle | 100 mm WD | 200 mm WD | 300 mm WD |
|---|---|---|---|
| 21° | 37 mm | 74 mm | 111 mm |
| 32° | 57 mm | 115 mm | 172 mm |
| 60° | 115 mm | 231 mm | 346 mm |
| 90° diffused | 200 mm | 400 mm | 600 mm |
What a tighter lens buys
Flux is conserved, so concentrating it into a narrower cone multiplies illuminance. The flat-top ideal scales with the square of the angle ratio: (90/30)² = 9. Measured heads land nearer 3×, because a diffused output is not an empty cone — it keeps a strong centre lobe inside its wide envelope — and every surface between LED and part costs some transmission. Budget 3× going from a 90° diffuser to a 30° lens at the same working distance and treat the rest as margin. The same squaring appears on the imaging side, where a lower f-number gathers more light.
Intensity converts straight into exposure: three times the light lets you cut exposure to a third at the same gain. For moving parts, peak illuminance is what freezes motion — the strobe overdrive guide and the duty-cycle matching guide cover the current side, and a tighter lens is the second lever, adding no heat.
A tight cone stings twice: its centre is hot with falloff toward the edge, which reads as uneven bright field, and direct light mirrors off shiny surfaces as glare. Alignment tolerance shrinks too — a 21° beam aimed a few degrees off walks its spot off the part.
The spot range prints the angle per model: the LS-SPT-0024 carries a 32° lens at 455 nm over a 49.9 × 66.6 mm lit area, and the LS-SPT-0037 tightens to 21° at 505 nm on a 99.9 × 141.6 mm lit area. For fields measured in single-digit millimetres, the LS-SPT-0175 is a 6 mm high luminance spot rated at 5 W.
Three focused heads across three lens angles:
- Size
- Under 50 mm
- Voltage
- 24 V
- Size
- 50-100 mm
- Voltage
- 24 V
- Size
- Under 50 mm
What a diffuser costs — and when it pays
The cost is peak illuminance — the 3× above — plus scatter. A diffuser sends some photons outside your cone and some straight into the lens, which reads as haze across flat, glossy surfaces. A crossed polarizer on the lens recovers that contrast at a further intensity cost; the cross polarization guide shows the set-up.
The payoff is an envelope. Curved, shiny and wrinkled surfaces illuminate without mirror hot spots, alignment forgives a few degrees, and wide fields stay even. Domes and cloudy-day lights push diffusion to its limit — the dome light guide and the shiny metal pins guide cover those cases. On the bench, the fastest test is a frosted film held in front of the light you already have: if the glare disappears and the exposure budget survives, diffused is the answer.
For whole-enclosure diffusion — light boxes and AOI rings — the special lights category collects those geometries.
Bar lights carry both options in one range: the LS-BAR-0400 is a 312 × 30 mm high luminance bar of standard type at 24 V, while the LS-BAR-1276 is a 372 × 28 mm diffused white bar, also at 24 V.
Standard optics for punch, diffused for envelope:
- Size
- 200-400 mm
- Type
- Standard
- Size
- 200-400 mm
- Type
- Diffused
Lens material: UV and heat
Beam shaping only pays while the optic survives its environment. Acrylic and polycarbonate lenses yellow under UV exposure and craze near heat, which cuts transmission and drifts the output colour over months of use. Optical-grade silicone resists that ageing and holds its shape and transmission from the UV-A band into the near infrared, which is why UV and high-current heads are built with it. The spot and bar ranges list 365 nm and 395 nm UV wavelengths; on any UV or hot application, treat the lens material as part of the specification.
Choosing: five situations, five answers
| Situation | Choose | Why |
|---|---|---|
| Matte part, short exposure, fast line | Focused / standard lens | Highest illuminance into a defined footprint |
| Shiny, curved or wrinkled surface | Diffused, or a dome | Envelope kills specular hot spots |
| Small field, longer working distance, cramped mount | Focused spot | Footprint sized by D = 2 × WD × tan(θ/2) |
| Large field, uneven part height | Diffused bar or light box | Even coverage, forgiving alignment |
| Motion blur you cannot expose away | High-luminance standard head, strobed | Peak illuminance freezes motion |
The cramped mount is the compact-lighting case — the compact lighting guide covers the mounting side. Shape is the first axis and wavelength the next: the color wheel guide maps which LED color suppresses which surface, and the geometry selection guide sets the angle to the part. Work them in that order — diffusion cannot fix the wrong wavelength.
Worked example: one bracket, two surfaces
Field of view 45 mm across, working distance 120 mm, exposure budget 1 ms, part a die-cast cap of Ø38 mm — in a matte bead-blasted version and a polished version.
Target footprint with overfill: 45 × 1.3 ≈ 59 mm. Required angle: θ = 2 × atan(29.5/120) = 2 × 13.8° = 27.6°. The nearest printed angle is 32°. Its footprint at 120 mm: D = 2 × 120 × tan(16°) = 240 mm × 0.287 = 69 mm — 53% overfill, comfortable. A 21° lens would give 240 mm × 0.185 = 44 mm, smaller than the field itself: far too tight.
Matte version: a 32° standard lens is right. Direct illumination delivers roughly 3× the illuminance of the diffused alternative, and a 0.3 ms exposure does the job.
Polished version: the same 32° direct beam mirrors the LEDs straight into the lens as a glare streak. Switch to diffusion and pay the ~3× penalty: the exposure becomes 0.3 × 3 = 0.9 ms, still inside the 1 ms budget. If the polish still streaks, the next step is a dome or a polarizer, not more gain.
Decision: same camera, same working distance — a 32° focused lens for the bead-blasted cap, a diffused head for the polished one.
Checks before you order
- Compute the footprint at your real working distance and hold it near 1.3-1.5 × the field of view.
- Shortlist by printed lens angle or diffused type, not by head shape — "spot" and "bar" describe the housing, the optic describes the light.
- Filter for the wavelength you need at that size; not every color ships in every angle and length.
- Match voltage and connector to your controller; most heads in the spot and bar ranges run from 24 V.
- If you will strobe to recover diffuser loss, run the duty-cycle numbers at your overdrive current before wiring.
- Leave tilt and rotation adjustment in the bracket: narrow beams punish aim, diffused ones barely care.
When the usual answer is wrong
"Focused is brighter, so it is always better." On a specular surface the extra photons arrive as a mirror streak you then have to polarize away; start diffused and spend the exposure instead.
"Diffused means blurry." Diffusion shapes illumination, never focus; the imaging lens sets focus.
"The light's beam angle should match the camera's field-of-view angle." The two are independent — the light does not image, only the footprint at your working distance matters, and moving the working distance moves it. The working distance extension guide shows how framing and distance move together.
"Diffusion will fix my contrast." Geometry decides contrast first: a diffused flood at the wrong angle still fails. See the surface-or-silhouette guide before spending on diffusion.
Size the footprint first, then buy intensity only where the surface can use it. The lights finder filters by size, wavelength and voltage, the lighting topic page collects the geometry guides, and the configurator starts at the light step:
The configurator matches a camera, lens, light, light controller and cables to each other, step by step, and lists only parts that fit what you already picked.
If the surface resists both options, describe the part and the failure mode through the contact page.
Questions
Does a diffuser on the light change the camera's focus?
No. Focus and depth of field belong to the imaging lens and its aperture; the diffuser only spreads light before it reaches the part. The two are independent, so you can pair a heavily diffused light with a sharp, low f-number lens. If a diffused set-up looks soft, suspect the imaging side: check focus, aperture and working distance before blaming the diffuser.
Can I widen a focused spot's footprint without changing the light?
Yes — move it back. Footprint grows linearly with working distance: the same 32° lens that covers 57 mm at 100 mm covers 115 mm at 200 mm. The price is intensity: average illuminance across the footprint falls roughly with the square of the distance, so exposure time or gain must rise to compensate.
Is a higher-wattage light always brighter at the part than a tighter lens?
Usually not. Electrical power sets only the total flux; the part sees that flux divided across the beam's footprint. Narrowing the cone multiplies illuminance roughly with the square of the angle ratio, so a tight lens on modest LEDs can out-illuminate a wide diffuser on more watts — with less heat and no extra current.
Do UV lights need special lens material?
Yes. Acrylic and polycarbonate windows yellow under UV and craze with heat; a yellowed window cuts 365-395 nm output and drifts the output colour. Optical silicone resists that ageing and holds transmission into the UV-A band. For UV work, treat lens material as a specification item and confirm it before mounting the head somewhere hot.
What beam angle covers a 40 mm field of view at 150 mm working distance?
Target a footprint about 40% larger, so about 56 mm. θ = 2 × atan(28/150) = 2 × 10.6° ≈ 21°. A 21° lens fits almost exactly at that distance; a 32° lens covers 86 mm and is the safer choice if the part or bracket sits slightly off-axis. Re-run both formulas at your own working distance before ordering.