Understanding laser power: what watt figures really tell you
are explained briefly when you hover over or tap them.
The wattage is in the product name of almost every laser engraver. But it says less than it seems. What matters is which power is meant, what area it hits and which type of laser is behind it.
Optical and electrical power
A laser converts electrical energy into light. A large part is lost as heat in the process. Only the light counts for the material, that is the optical power (output power). The electrical power is what the module draws from the power supply.
A few years ago, many diode laser sellers advertised with the electrical power or with an “equivalent” figure. A module with 5 W of optical power was then called “40 W”, one with 10 W optical “80 W”. You can still find such offers today for replacement modules in online shops, where the optical power is often only given in brackets or in the small print.
Reputable manufacturers now state the optical power, and the device names refer to it. Check anyway:
- Do the technical data explicitly say “optical power” or “output power”?
- Does the number fit the power consumption of the power supply? If the power supply delivers 48 W, the module cannot emit 40 W of light.
- Does the manufacturer give cutting values that match the power?
In our device overview, the optical power of the main source is listed for every device.
What more power gives you
More optical power means more energy per unit of time. This mainly affects two things:
Cutting. With more power you cut thicker material or need fewer passes. An example from the manufacturer information: the xTool S1 20W cuts up to 10 mm of cherry wood in one pass, the 40 W version up to 18 mm. On the xTool M2 it is 8 mm of basswood with 10 W and 10 mm with 20 W. Double the power therefore does not mean double the cutting depth.
Speed. An engraving that works with 10 W at 100 mm/s can be done at a higher speed with 20 W. This only applies if the mechanics keep up, though. Many gantry diode lasers are limited to 400 to 600 mm/s. Then more power saves little time when engraving, because the machine cannot move any faster.
What more power does not give you: finer details. For fine engravings on thin material, too much power is even a hindrance. You then have to turn it down a lot, and some machines work unevenly in the low percentage range.
Spot size and power density
What matters for the effect on the material is not the power alone but the power density: power divided by the area of the laser spot. The smaller the spot, the more concentrated the energy.
With diode lasers the spot usually grows with the power. xTool gives these spot sizes for the S1 variants:
| Variant | Spot size | Area (as a rectangle) | Power density, roughly |
|---|---|---|---|
| 10 W diode | 0.06 x 0.04 mm | 0.0024 mm² | approx. 4,200 W/mm² |
| 20 W diode | 0.08 x 0.06 mm | 0.0048 mm² | approx. 4,200 W/mm² |
| 40 W diode | 0.08 x 0.10 mm | 0.008 mm² | approx. 5,000 W/mm² |
| 2 W infrared | 0.03 x 0.03 mm | 0.0009 mm² | approx. 2,200 W/mm² |
The calculation is simplified, because a real laser spot has no sharp edges. But it shows the point: the power density hardly rises with more watts. The larger spot spreads the additional power. That is why a 10 W laser often engraves fine lines just as well as or better than a 40 W laser, while the 40 W laser is clearly ahead when cutting.
For the power density to be right, the focus must be set correctly. One millimetre too high or too low and the spot becomes much larger. More on this in the article Laser focus.
Why strong diode lasers are combined
A single blue laser diode typically emits only a few watts. Strong diode lasers therefore combine several diodes and merge their light into one spot with optics. Two examples from the manufacturer information:
- The xTool D1 Pro 20W combines 4 diodes of 5 W each.
- The Creality Falcon2 22W uses 4 diodes of 6 W each and compresses the beam with FAC optics (fast axis collimation).
The combining has consequences:
- The spot becomes larger and often rectangular. Fine details lose some sharpness.
- The optics lose part of the power. On the Falcon2, 4 x 6 W adds up to 24 W, while 22 W is stated.
- Some machines can be switched to half power, for example from 40 W to 20 W or from 70 W to 35 W. In the smaller mode fewer diodes work and the spot becomes finer.
Comparing watts between laser types
Watt figures can only be compared within one laser type. A 55 W CO₂ laser cuts clear acrylic, which a 40 W diode laser cannot process at all because the blue light passes through. A 5 W UV laser engraves glass cleanly where a 20 W diode laser fails. And a fibre laser with 20 W marks stainless steel in seconds, while a diode laser of the same power needs spray for it.
With fibre and UV lasers there is also the fact that they work in pulses. The watt figure there is the average power. Each individual pulse contains a much higher peak power.
Which type can do which material is explained in the article Laser types compared.
What this means for your settings
Power is set as a percentage in the software. 50 % on a 10 W machine is something completely different from 50 % on a 40 W machine. Settings from videos or forums therefore only fit if machine, power and material match. Take other people’s values as a rough starting point and laser a test grid with different power and speed levels on every new material.
Continue with: Gantry or galvo and Laser parameters