Laser LPI Test: Line Interval Test for Engraving (Free) · CutCatVector

Free tool · no sign-up · LightBurn file with settings

Laser LPI test

How close should the engraving lines be? Burn one small grid: each column has its own line interval (lines per inch), each row its own power. Pick the square with even tone and no stripes, and use that LPI for fills and photos.

Your laser

Laser type
W

Optical output power, as printed on the laser module or tube. Diode means a blue diode laser (about 450 nm).

Material and engrave settings

%

Your engrave settings from the material test, if you have them. Otherwise this is a starting point, not tested on your machine.

Test grid

Bigger squares are easier to judge but take longer. Lines per inch are the same in mm and in.

Illustration, not a forecast. Lines are drawn far apart so you can see them: stripes on the left, merged lines on the right. Your burn depends on the beam, focus, speed and material.

Free, no email needed.
  1. Focus first (see the focus test): out of focus, every square looks wrong.
  2. LightBurn: File › Open (not Import). Every square already has its line interval, power and speed. Check Preview, run Frame, then start.
  3. SVG carries shapes only. In your laser software give every colour Fill / Engrave with the line interval (or LPI) and power from the table.

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Read your test

  1. Pick the row (power) with a good tone and no burnt or damaged surface.
  2. In that row, go from left (coarse lines) to right (fine lines).
  3. Pick the first square where the lines touch with no gaps. Further right they only overlap more: darker and slower.
  4. Check it under a magnifier. Click the picked square again to clear it.

Pick the best square

None fits? · · · · ·

Your line interval

Material Pick a square Nothing is picked, so nothing is passed on to the photo tool.

How it works

  1. Choose your laser, its power and the material. Put in your engrave power and speed if you know them.
  2. Download the LightBurn file, focus, and run it. Each column is a different line interval, each row a different power.
  3. Pick the row with a good tone, then the first square in it where the lines touch. Use that line interval for fills, and as a starting DPI for photos.

Tips

  • More LPI is not better. Past the point where lines merge, a square only gets darker, deeper and slower. Photos turn muddy.
  • Zig-zag edges on the squares mean the back-and-forth lines do not line up: that is the scanning offset in LightBurn, not the LPI.
  • Photos: start with the image DPI = your LPI, so each pixel row is one laser line. A photo also depends on the dither pattern and the material: burn a small patch first. A test with dithered tones comes in the next version.
  • Labels are scored at low power with a test ID, the material and the speed, so the scrap still makes sense in a month.

FAQ

What is LPI?

Lines per inch: how many engraving lines the laser puts in one inch. LightBurn calls the same thing "Line interval" in mm. Line interval = 25.4 ÷ LPI, so 254 LPI is 0.1 mm.

LPI, DPI and line interval: the same thing?

Line interval (mm) and LPI describe the same spacing of the laser lines. DPI belongs to an image: how many pixels per inch. When the image DPI equals the LPI, each pixel row becomes one laser line, which is a good starting point for photos.

Does the LPI I find work for photos?

It is a good starting point. A photo also depends on the dither pattern, the beam, the power and the material, so burn a small patch of the photo first and adjust. This test uses solid fills; a test with dithered tones is planned.

LightBurn has its own Interval Test. Why use this one?

It works the same way for solid fills. Here you also get a starting power and speed for your laser and material, a test ID and labels on the scrap, a page to read the result step by step, a finer test around your pick, and a link to the photo tool with your result.

Does it work with xTool Creative Space or Glowforge?

The SVG carries the squares, one colour each; the line interval, power and speed are in the table, and you set them by hand. Whether you can type an exact interval depends on the program: some offer only fixed resolutions or "lines per cm". Check what your software allows.

mm/s or mm/min?

LightBurn shows either, depending on your settings. Many diode lasers use mm/min. Pick the same units in Advanced settings. 1 mm/s = 60 mm/min.

Inches or millimetres?

Switch mm / in next to "Test grid". It changes the square size and labels you see, not the LPI. Speeds stay in mm/s or mm/min, like in LightBurn.