LightBurn Speed, Power, and Passes Explained

The Three Controls

Every laser cut and engrave comes down to three variables: how fast the head moves, how much power the laser outputs, and how many times it crosses the same path. Understanding what each actually does — not just trial-and-error until something works — dramatically shortens the time to good results.

Speed

Speed is how fast the laser head moves across the material, usually in mm/min (diode lasers) or mm/s (CO2 lasers). These are the same unit — just convert: 1000 mm/min = ~16.7 mm/s.

Slower = more energy delivered to one spot = deeper cut or darker burn.

But slower is not always better. On wood, going too slow burns the surrounding grain, widening the kerf and producing a charred brown halo instead of a clean dark line. On acrylic, going too slow melts the walls and causes the cut to re-fuse as the head passes.

Faster = less energy = shallower, lighter result. Too fast and you don't cut through. For engraving, you lose depth and contrast.

Find the sweet spot where the material processes cleanly without over-burning adjacent areas.

Power

Power is the percentage of the laser's rated wattage being applied. 100% on a 20W diode laser is 20W. 50% is 10W.

Important: power isn't linear on most diode lasers. The response curve between 5% and 95% is roughly linear, but behavior at the very bottom (0-5%) and very top (95-100%) is less predictable. Most diode lasers need a minimum of around 10-15% before they actually fire with any consistency.

Never run diode lasers at 100% continuously for long jobs. Sustained 100% shortens laser module life. For most cutting, 80-90% achieves full cutting power. For large engraving fill jobs, 40-60% is safer.

CO2 lasers tend to have more linear power response and can run at higher percentages longer.

Passes

A pass is one complete run of the laser over a path. Two passes doubles the total energy delivered.

When to use multiple passes:

• Cutting thick material where a single pass doesn't go through
• Achieving darker, deeper engraving
• When you want clean char-free edges (second pass at higher speed/lower power as a cleanup)

Why multiple passes is sometimes better than one slow pass:

• Less heat buildup per pass — surrounding material cools between passes
• Cleaner walls — each pass enters fresh material rather than scorched residue
• More consistent depth

Downside: More passes = more time. Slower is usually faster than more passes for most materials.

How They Interact

The relationship between speed, power, and passes is multiplicative. These all deliver roughly the same total energy:

But the results aren't always identical — slower passes burn differently than faster multiple passes. Test to find what your specific material prefers.

Air Assist

Air assist blows air at the cut point. It does several things:

• Clears smoke and debris from the kerf, letting the laser reach fresh material
• Cools the cut walls, reducing char and heat damage to surrounding material
• Prevents flare-ups on paper, cardboard, and resinous woods
• Significantly reduces required power or passes for cutting

Running without air assist on a wood cut often requires 20-30% more power or an extra pass to achieve the same result. Always run air assist for cutting. For engraving, you can run it lower or off to achieve warmer/darker marks on wood — the smoke deposits back and creates a richer engrave.

Line vs Fill vs Image Modes

In LightBurn's layer settings:

Line (Cut) — the laser follows vector paths once. Used for cutting outlines, single-stroke engraving, and text outlines.

Fill — the laser rasters back and forth to fill a shape. Used for engraving solid areas. Speed/power settings apply to the fill strokes. LPI controls the line spacing.

Image — raster mode for photos. Same back-and-forth as fill but driven by pixel values.

Offset Fill — fills shape with progressively shrinking offset paths instead of raster lines. Good for engraving items where you want to avoid the direction-of-travel pattern.

Building a Material Library

Once you find settings that work, save them in LightBurn's material library:

Edit → Material Library → New Entry

Name it descriptively: "Basswood 3mm Cut - Ray5 20W - 500/95%/1 pass". Include the machine, because settings don't transfer between different lasers.

Over time this library becomes your most valuable asset — tested settings you can pull instantly instead of running test burns every session.

Starting Points for Common Jobs

*For a 20W diode laser. Adjust proportionally for other wattages.*