Choosing a Laser
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If you can answer these questions, you can greatly simplify the task of choosing the proper laser. 

Are you working indoors, outdoors, or both?

If you are indoors, you will want a highly visible beam laser that can be used without an electronic laser receiver. If you are primarily outdoors, you will have to use a laser receiver, as even the brightest visible rotating beam will be lost in daylight. Infra-red, red, and green beams are all employed in construction lasers. Infra-red light is invisible to the human eye, which means that an electronic laser receiver must be used. Infra-red beams are most often found on lasers employed for outdoor work, such as grading, trenching, or setting concrete forms. The visible red and green beams are usually found on lasers employed in interior work, such as drywall, drop ceiling installation, or partition installation. Red beam diodes are less expensive and most prevalent. You will see red beam wavelengths of 650nm or 635nm. If you want to use a laser without a receiver, make sure it has a 635nm red beam and variable rotation speed. If you cannot slow the beam rotation speed, the laser is not designed for visible interior work. The human eye is more sensitive to the 635 wavelength than 670, and is even more sensitive to green light. The downside is that the diodes that produce green beams are expensive, must operate within a narrow temperature range, and at this time are much more fragile than red or infra red diodes.

On the job, are there things that can disturb the laser such as laborers, live traffic, heavy equipment?

If your typical job is the larger commercial site, you should have a self leveling laser. With a manually leveled laser, the user will have to periodically return to the laser and re-center the level bubbles. This is not necessary with a self leveling laser. A self leveling laser will also shut itself off if disturbed. This prevents taking a grade shot when the laser is out of level. Both servo motor self leveling and compensated self leveling provide the same results. There are pluses and minuses to each system. If you are placing the laser up on a 12 foot tripod for machine control work or overhead for suspended ceiling installation, a servo leveled laser is handy because it does not have to be rough leveled. Servo systems are more complex electronically and consume more power than compensated systems. 

What type of accuracy do you need?

Rotary laser accuracy specifications start at ±1/4 inch @ 100 feet for inexpensive manually leveled lasers, and improve to ±3/32 inch or ±1/16 inch @ 100 feet for self leveling lasers. The former is sufficient for house foundations, while the latter are suited to larger jobs and commercial buildings. Don't forget that if high accuracy is desired, stay close to the laser.

Do you tend to be shooting all day long off one laser set up and what is the typical maximum distance from the laser that you would be working at?

If you are on the larger commercial jobs and are using the same laser set up all day, your choice should be a self leveling laser. Users of manually leveled lasers must periodically return to the instrument and check the level vials. On larger jobs, it is not always convenient to have to return to the laser. On the other hand, the small contractor working on a house foundation is typically not far from the laser, and tends to use the laser for shorter periods. Thus under these circumstances, manually leveled lasers can be used with excellent results.