mW Laser Meaning – Here’s The Definition Of mW in Lasers?

When it comes to laser technology, a terminology you will see very often is the mW – or milliwatts.

But what is it and what is its significance when used in the context of laser technology?

In this article, we will explore this topic.

The mW, or milliwatt, is 1/1000 of a watt. It is an important measurement unit in laser technology as it is used to rate the power output of different types of lasers.

Defining the Watt

The Watt is a unit of measurement used to measure power. According to, the Watt is a “unit of power in the International System of Units (SI) equal to one joule of work performed per second, or to 1/746 horsepower”.

For example, if an electrical conductor is carrying one Ampere (1A) of current with a difference of one volt (1V) between points, then it would have a power of 1 Watt (1W).

This unit of measurement is named after the British engineer and inventor, James Watt. Almost all devices that rely on electricity as a source of power will use the Watt as a unit of measurement.

Volts, Amps, and Watts Explained

What is mW in Lasers?

There are other sub-unit measurements of the Watt, such as the commonly seen kilowatt (kW) that is used to calculate your electricity bill. 1 kW is equivalent to 1,000 Watts.

When it comes to laser technology, the one you will see is the mW instead.

The mW, or milliwatt, is 1/1000 of a watt. It is an important measurement unit in laser technology as it is used to rate the power output of different types of lasers.

Indirectly, a laser’s power output rating also determines which class they belong to. It’s important to know the mW rating of a laser so that you are aware of what you are dealing with.

Laser Pointer Wattage – The Relevance of mW in Laser Technology

In general, most lasers below Class 4 are limited to no more than 5 mW of power output. A lot of Class 1 lasers that don’t have visible beams have very low power output, being limited to less than 1 mW. This is the same for Class 1M and Class 2 lasers, which may emit either visible or invisible beams.

However, Class 3A is where you start to see lasers with a power output of between 1 and 5 mW, while Class 3B lasers can have the power output ranging from 5 to 500 mW. As for Class 4 lasers, these are very hazardous because the power output rating is more than 500 mW.

Even in the USA, where laws on laser tech ownership for the public are generally not very strict, Class 4 lasers are limited to professional or military use. When it comes to laser pointers for consumer use, they have to be Class 3A and below.

If you’re interested, we have also previously touched on the different laser classes, the damage potential of a 5 mW laser, and federal rules on laser pointers.

Laser Power Measurement

How is a laser’s power output measured? Of course, equipment that can measure them exist. Measurement equipment that can detect a laser’s power output uses a sensor that transfers or converts the laser’s energy output into electricity. Then, the system is connected to a computer or meter that displays the mW reading of the current detected.

There are two types of systems that are used for such measurements: photodiodes or thermopiles. The first type, photodiodes, is much more sensitive and is suitable for measuring the output of low-power lasers, including laser pointers. These can measure up to a few Watts in total power output.

Then there’s the thermal-based thermopile, which is used to measure lasers with an output of up to the kilowatt (kW) range.

Ebay Lasers measured on Laser Power Meter

Differences in Power Output

The power output of a laser can greatly affect its visible aspects. Changes in brightness and heat intensity are the most commonly observed differences.

In general, a laser that has a higher mW rating will have a brighter beam and will burn hotter. With a high enough power output, lasers can even burn skin or damage your eyes if looked into directly without blinking.

When it comes to smaller items like basic laser pointers or pens, the power output is usually around 1 mW.

Most laser tag entertainment centers also use laser tag guns which emit infrared light, or those with a visible beam of 1 mW or lower. This is to comply with safety regulations.

Of course, there are many different types of lasers pointers, some of which have a power output of 5 mW or more. Larger handheld laser pointers with 2,000 mW power output are actually available for purchase online! At this power rating, the laser can easily damage camera sensors or cause permanent damage to your eyes.

Check with your local authorities if you wish to purchase a laser pointer as powerful as this – you would most likely need to apply for a permit or license of some sort.

Read more: What does nm mean in Lasers?

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