Valid information about the performance of a laser is the foundation for its proper use. As the variety of commercial lasers increases, users need a greater overall understanding of how to measure their output. Sensors, readouts and test setup can affect your accuracy when measuring laser power and other critical parameters. In applications such as materials processing, environmental monitoring and confocal microscopy, understanding the laser's performance is critical. For example, a laser that operates erratically as it drills holes in steel could fail to penetrate the metal or produce holes that are too large or too small. A laser whose output is misunderstood could produce misleading spectroscopic data. A laser whose power is even slightly too high could destroy a fragile biological specimen. Measuring optical power is often simple. You can obtain a valid reading by using the appropriate sensor and readout and controlling any environmentally induced errors.