Skip to content Laser cutter power is one of the most misunderstood specifications on a laser machine. A machine may be sold as 50W, 80W or 100W, while the software asks you to enter a percentage. At the same time, a glass CO₂ tube is normally limited by current in milliamps, and the power that actually reaches the material can be lower than the value printed on the tube.
This guide separates those different meanings of “power” and explains how they relate to cutting, engraving, tube life and real-world performance. It also retains my original method for setting the safe maximum power percentage on a Ruida-controlled CO₂ laser.
Quick answer: what does laser cutter power actually mean?
When a laser machine is described as 50W, 80W or 100W, that figure should refer to the optical output power of the laser source, not the electrical power consumed by the whole machine.
However, the percentage shown in RDWorks or LightBurn is a controller command. It is not a calibrated wattmeter. Setting a 100W laser to 50% does not automatically mean that 50W is reaching the material.
- Rated laser power — the nominal optical output of the source, for example 80W.
- Controller power % — the command sent by the controller or software.
- Tube current — the electrical current through a glass CO₂ tube, normally measured in mA.
- Measured optical power — the laser power actually leaving the tube or reaching the workpiece.
Why 50% power does not necessarily mean 50% of the rated watts
The power percentage shown in laser software is best treated as a control value, not a direct wattage reading. The relationship between commanded percentage, tube current and optical output depends on the laser source, high-voltage power supply, controller configuration and the individual tube.
On glass CO₂ systems, two apparently identical tubes can need different percentage values to reach the same recommended current. I have seen machines where the useful maximum controller setting falls anywhere from roughly 50% to more than 90%. That is why copying another user’s “maximum percentage” can be misleading.
The safe reference point is the laser tube manufacturer’s recommended operating current, combined with an actual current measurement and, ideally, a laser power measurement.
Rated power, maximum power and useful operating power
Laser tube manufacturers commonly distinguish between rated or target power and a higher maximum output figure. They also specify a recommended current and a separate maximum working current.
For example, SPT lists its T90 as a 90W tube with a higher maximum output figure, while also specifying 22mA as the recommended current and 25mA as the maximum working current. The T100 is listed at 100W with a recommended current of 24mA and a maximum working current of 25mA.
The important point is that “maximum” is not the same as “recommended continuous operating point”. Running a tube harder than necessary for routine work can shorten its life without giving a useful increase in cutting performance.
How much laser power do you actually need?
There is no single wattage that is right for every user. The useful power level depends on the material, thickness, required speed, edge quality, duty cycle and whether the machine is mainly cutting, engraving or doing both.
| Typical requirement | What matters most |
|---|---|
| Fine engraving | Good low-power control, small spot, stable motion and suitable firing threshold |
| 3–6mm acrylic or wood | Enough optical power to cut cleanly at a useful speed, plus good focus and air assist |
| Thicker acrylic/wood | More power can increase speed and cutting margin, but optics and focus become increasingly important |
| Production cutting | Power, duty cycle, cooling, extraction, acceleration and workflow all matter |
| Metal cutting | Laser technology, wavelength and assist gas dominate; CO₂, fibre and diode wattages are not directly interchangeable |
More watts can make a machine faster or allow thicker material to be processed, but power alone does not guarantee a better result. Poor focus, dirty optics, weak extraction, insufficient air assist or bad material can make a higher-powered machine perform worse than a well-set-up lower-powered one.
Power and speed work together
Cut quality is governed by the amount of laser energy delivered to a given area of material. Power and speed therefore have to be considered together.
At the same optical power, slowing the machine generally increases the energy delivered per unit length. Increasing speed reduces it. That is why a setting cannot sensibly be described by power percentage alone.
Focus, beam diameter, lens choice, air assist, material type and material thickness then modify the result further. This is why material-test matrices are normally more useful than copying a single “magic” setting from somebody else’s machine.
Maximum power and minimum power on Ruida controllers
Ruida controllers use both maximum and minimum power. The controller can ramp between those values as the head accelerates and decelerates.
At low cutting speeds, the machine may spend much of the move at or near the minimum-power value. If minimum power is below the tube’s firing threshold, the laser may fail to fire properly in corners or short moves. For slow cutting operations, using the same minimum and maximum power can therefore be appropriate.
For engraving, the opposite problem can occur: excessive minimum power can over-burn corners and direction changes. This is one reason it is important to understand what the controller is doing rather than treating “power %” as a simple fixed wattage.
How to measure the real laser power
The only reliable way to know the optical output is to measure it with a suitable laser power meter. A milliammeter tells you how hard a glass CO₂ tube is being driven electrically, but it does not directly tell you how many watts are leaving the tube.
For troubleshooting, it can be useful to measure power at the tube and again near the workpiece. A large difference can point towards contaminated, damaged or misaligned mirrors and lenses.
Power measurement is also useful when a tube is ageing. If the current is normal but measured optical output has fallen, the tube itself may be deteriorating. If power is good at the tube but poor at the workpiece, the optical path deserves attention before replacing the tube.
CO₂, diode and fibre laser watts are not directly comparable
A watt is still a watt, but the practical effect of that watt depends strongly on wavelength, beam quality, spot size, pulse behaviour and how well the material absorbs that wavelength.
A 20W visible diode laser, a 20W CO₂ laser and a 20W fibre source can therefore behave very differently on the same material. Clear acrylic, for example, absorbs CO₂ laser radiation strongly but transmits much of the visible light used by common blue diode lasers. Metals respond very differently again.
When comparing machines, compare the laser technology and application as well as the wattage figure.
How to set a safe maximum power percentage on a glass CO₂ laser
There is a lot of confusion over what maximum power percentage you should use on a glass CO₂ laser tube if you want to preserve tube life. The safest way is not to rely on a generic percentage. Measure the tube current and compare it with the manufacturer’s recommended operating current.
What do you need?
- A milliammeter connected in series with the laser tube ground/cathode return.
- The manufacturer’s recommended operating current for your exact tube model.
For example, SPT specifies a recommended current of 22mA for the T90 and 24mA for the T100, with a maximum working current of 25mA for both models.
RECI also publishes recommended currents for its W-series tubes. These values should be checked against the latest documentation for the exact tube fitted to your machine rather than copied from another model.
How to determine your maximum usable power percentage
With the milliammeter fitted and the correct recommended current confirmed, run the laser at a series of controller power settings and note the tube current at each setting. The point where the current reaches the manufacturer’s recommended value becomes the practical maximum controller percentage for that tube and power-supply combination.
For my SPT T50W tube, the recommended current is 18mA and the maximum working current is 20mA. On my machine, 18mA corresponded to a controller setting of approximately 59%.
Do not be concerned if your value is very different. I have seen large differences between machines using nominally similar tubes. That variation is exactly why the current should be measured instead of assuming that a fixed percentage applies to every machine.
If your machine cannot reach the recommended tube current even at the top of its usable power range, the high-voltage power supply may be undersized, limited or faulty. Conversely, increasing the controller percentage beyond the point where the tube has already reached its recommended current is not a sensible way to gain performance.
Limiting maximum power in RDWorks
If your machine uses a Ruida DSP controller, you can set a maximum laser power in the controller’s vendor settings. This means that even if an operator enters a higher job power, the controller will limit the available output to the configured maximum.
Before changing vendor settings, save a backup of the controller configuration. These settings are normally configured by the machine manufacturer and should only be changed when you have a clear reason to do so.
In RDWorks, connect to the machine, open the Vendor Settings, read the current controller configuration, then locate the laser parameters and set the maximum power to the value established from your current test.
Write the change back to the controller only after checking the value carefully.
Limiting maximum power in LightBurn
For a Ruida-controlled machine in LightBurn, open Machine Settings with the laser connected. Read the current machine configuration, expand the Vendor Settings section and locate the laser settings.
Back up the settings before making changes. LightBurn itself warns that vendor settings are normally configured by the manufacturer and should generally be left alone unless you know why you are changing them.
Set the laser maximum-power value to the percentage established from your current measurement, then write the settings back to the controller.
How to fit a milliammeter to a CO₂ laser cutter
A milliammeter is normally installed in series with the cathode return side of the glass laser tube circuit. Although this is the return side, the laser power supply still operates at potentially lethal high voltage, so the machine must be isolated from the mains before any electrical work is carried out.
If you are not competent to work safely around high-voltage laser equipment, have the meter fitted by a qualified technician. Do not work on the machine while it is connected to the mains.
Common laser power mistakes
- Assuming 50% in the software means 50% of the rated watts.
- Running a glass CO₂ tube at the manufacturer’s maximum current instead of its recommended current.
- Increasing power to compensate for dirty or misaligned optics.
- Comparing diode, CO₂ and fibre machines by wattage alone.
- Copying another machine’s settings without considering speed, spot size, material and actual optical output.
- Assuming a higher-power machine will automatically engrave better.
Frequently asked questions
Does 50% power on a 100W laser mean 50W?
Not necessarily. The percentage is a controller command, not a calibrated optical watt reading. The actual output depends on the source, power supply, controller configuration and condition of the laser.
Is it safe to run a CO₂ laser at 100%?
Only if 100% has been deliberately configured so that the tube remains within the manufacturer’s recommended operating current. On many machines, the raw controller scale allows the tube to be driven harder than is desirable for long-term use.
Does more laser power always cut better?
No. More available power can increase cutting speed or thickness capability, but focus, optics, air assist, material and motion settings can be equally important to edge quality and consistency.
How do I know if my laser has lost power?
Measure the optical output with a suitable power meter and compare it with previous readings. If tube current is normal but optical output has fallen, the source may be ageing. If output is good at the tube but poor at the workpiece, inspect the optics and alignment.
Conclusion
Laser power is more complicated than the wattage printed on the machine or the percentage shown in software. For a glass CO₂ system, the most useful approach is to separate rated optical power, controller percentage, measured tube current and actual optical output.
Once those are understood, you can set a sensible maximum current, protect the tube, diagnose power loss more accurately and make more meaningful decisions about cutting and engraving settings.
If you are working specifically with acrylic, see How to Laser Cut Acrylic for material-specific guidance.
What Next?
Did you enjoy this post? Why not check out some of our other posts:
Disclaimer
Last updated April 25, 2024
WEBSITE DISCLAIMER
The information provided by n-Deavor Limited, trading as Laseruser.com (“we,” “us” , or “our”) on (the “Site”) is for general informational purposes only. All information on the Site is provided in good faith, however we make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability or completeness of any information on the Site.
UNDER NO CIRCUMSTANCE SHALL WE HAVE ANY LIABILITY TO YOU FOR ANY LOSS OR DAMAGE OF ANY KIND INCURRED AS A RESULT OF THE USE OF THE SITE OR RELIANCE ON ANY INFORMATION PROVIDED ON THE SITE. YOUR USE OF THE SITE AND YOUR RELIANCE ON ANY INFORMATION ON THE SITE IS SOLELY AT YOUR OWN RISK.
EXTERNAL LINKS DISCLAIMER
The Site may contain (or you may be sent through the Site) links to other websites or content belonging to or originating from third parties or links to websites and features in banners or other advertising. Such external links are not investigated, monitored, or checked for accuracy, adequacy, validity, reliability, availability or completeness by us.
WE DO NOT WARRANT, ENDORSE, GUARANTEE, OR ASSUME RESPONSIBILITY FOR THE ACCURACY OR RELIABILITY OF ANY INFORMATION OFFERED BY THIRD-PARTY WEBSITES LINKED THROUGH THE SITE OR ANY WEBSITE OR FEATURE LINKED IN ANY BANNER OR OTHER ADVERTISING.
WE WILL NOT BE A PARTY TO OR IN ANY WAY BE RESPONSIBLE FOR MONITORING ANY TRANSACTION BETWEEN YOU AND THIRD-PARTY PROVIDERS OF PRODUCTS OR SERVICES.
AFFILIATES DISCLAIMER
The Site may contain links to affiliate websites, and we receive an affiliate commission for any purchases made by you on the affiliate website using such links. Our affiliates include the following:
- makeCNC who provide Downloadable Patterns, Software, Hardware and other content for Laser Cutters, CNC Routers, Plasma, WaterJets, CNC Milling Machines, and other Robotic Tools. They also provide Pattern Files in PDF format for Scroll Saw Users. They are known for their Friendly and Efficient Customer Service and have a comprehensive back catalogue as well as continually providing New Patterns and Content.
- Cloudray Laser: a world-leading laser parts and solutions provider, has established a whole series of laser product lines, range from CO2 engraving & cutting machine parts, fiber cutting machine parts and laser marking machine parts.
