Every so often I'll visit another contractor's job site and see him using a spirit level or a water level for a task that could be done faster and more accurately with a line laser. The reason, I'm often told, is that lasers are too expensive. This is an answer I have a hard time accepting, because line lasers have become very affordable. I would no more work without one than I would work without a cordless drill.

For this article, my crew and I tested 11 self-leveling line lasers that can be purchased for $300 or less – an amount any tradesperson should be willing to spend for a tool that can pay for itself. Our pricing came from reputable online dealers; you may pay more or less based on when and where you buy the tool. We chose not to include point-to-point (dot) lasers, mostly because they're not as applicable to the tasks contractors perform every day.

How Line Lasers Work

A line laser contains diodes (typically one per line) that emit visible beams of light. This light passes through a focusing lens and then enters a prism that causes it to fan out along a single plane. When the light hits an object, it appears as a line. If you were to omit the prism, you'd have a point-to-point laser, and the light would come out as a focused beam that appeared as a dot.

Laser beams are either red or green. Red is more common because red diodes cost less, use less power, and will continue to work at lower temperatures. But green is more easily picked up by the human eye, so some lasers – usually expensive rotary models – use that color. All but one of the tools we tested project red beams. The exception is CST Berger's ILMXTG, which is the only green-beam laser in this price range.

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Modern line lasers are self-leveling, and the vast majority rely on pendulums to bring their beams to level. The diodes are attached to the pendulum, which swings on a pair of gimbals. When the pendulum comes to rest, the projected beams will be plumb and level.

The pendulum only works within a limited range; if the base of the laser is not within 4 to 6 degrees of level, the tool will be unable to level itself. When this happens, the laser will alert the user by sounding a beeper, rapidly flashing the beams, or shutting the beams down. If the laser has an indicator lamp, it will flash or shine red.

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Range and Accuracy

The lasers we reviewed are primarily intended for indoor use over short distances. Their beams are not bright enough to be seen from far away or under bright lighting conditions. The distance that a beam can project and still be visible depends on the amount of ambient light – and since the manufacturers don't know how bright it will be on any particular job site, they can only estimate range. We found that their estimates bore little relation to actuality – in many cases, they understated the working range of the laser. Because of this, we chose not to include those estimates in our specifications chart.

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Though green beams are said to be easier to see than red ones, green-beam lasers are costlier, burn through batteries more quickly, and may fail to work in very cold weather.

When comparing how the tools worked over short distances (15 to 20 feet), we didn't see any great difference in the brightness or width of the beams. We also tried them out at longer range, placing them side-by-side and projecting vertical beams onto a wall 55 feet away (the span of the longest indoor area we had access to). At that distance we began to notice some differences. For us, however, it would be highly unusual to use a line laser from such a distance.

The stated accuracy of these tools varies by model but is typically plus or minus 1/8 inch in 30 feet – a level of accuracy that is sufficient for most of the things we do. If you are one of those people who worry about 1/32 inch over 15 feet, then a line laser is not for you, and you'll need to spend more and get a rotary model.

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The author removed the housing from this PLS2 to show how line lasers work. The diodes are attached to a pendulum that swings from a set of gimbals. A magnet dampens the swinging motion of the pendulum and helps it come to level more quickly.

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Beams produced by diodes are sent through a pair of prisms that fan them into broad planes of light, which appear as lines where they land on a surface.

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This is what the beams look like when the tools are lined up and their vertical beams are projected 55 feet onto a textured plaster wall. The first four beams on the left are brighter and crisper than the rest.

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At 55 feet, most of the beams have spread to about 1/8 inch wide. These are the four brightest beams at that distance. Note how the beam from the Leica has spread to about 1/4 inch wide.