Laser technology sheds new light on the old tasks of determining plumb and level.

Construction lasers have been around for 20 years, but have only recently become more practical. Ten years ago, for example, the typical rotating laser cost as much as $5,000, looked like a suitcase and weighed about as much as one going on a family's week-long vacation.

But like all things electronic, they've gotten considerably smaller and less expensive, and, as a result, are becoming more and more popular on the jobsite. Contractors can pick up laser devices today that aren't much bigger than a tape measure on steroids. And they'll have plenty of models to choose from that cost well under $1,000.

In large part, the laser's light source helped dramatically downsize bulk and price. Early lasers used what amounted to light produced by a neon tube and required a 12-volt car battery to operate. Besides being power hogs, their glass tubes didn't make them durable devices to haul around a construction site.

Then in the mid-1990s, manufacturers switched to semiconductor diodes as the light source. These diodes are very much like what you'd find inside a CD player. As a result, laser devices not only got smaller, lighter and less expensive, but operate much more efficiently - often requiring no more than a couple of AA batteries for juice.

Lasers devices replace the tried-and-true level, plumb bob and chalk line, making quick yet accurate work out of taking precise measurements in the less than hospitable conditions of construction. The devices are particularly handy when the existing surface is uneven (often), but when everything above must be dead on accurate (always). We're not going to tell you not to use one in residential work, but from talking with manufacturers, it sounds to us like the lasers are best suited for the intermediate distance associated with commercial work. And maybe one of the biggest advantages is that one contractor can often work solo quickly laying out work, installing material and controlling the quality of the project.

"The first PCs to hit the market were expensive, intimidating and not very popular," says D. Michael Tramontin, director of marketing for Pacific Laser Systems. "We're past that point for lasers, but we're still adolescents in terms of product cycles."

Not Science Fiction

If you're unfamiliar with the products, keep in mind we're not talking about laser beams you'd see in a Star Wars movie. Unless you're outside on a foggy morning, you won't see a line through space. Lasers have to reflect off something to be seen, and only one family of lasers will shine an actual line on a wall or ceiling. In most cases you don't "see" a line at all, but rather a dot.

Lasers must also conform to FDA regulations that set safety standards for exposure to laser radiation. For the most part, the devices we're talking about fall into the government's Class IIIa rating, which means the radiation can't exceed 5 milliwatts. That's enough to produce a beam bright enough to be easily seen indoors, but not so much so outside in the sunlight. In many cases, devices designed for outside work use a less expensive infrared beam the eye can't see anyway that requires an electronic detector. Finally, while nobody's going to advise you to sit and stare at a laser beam for any length, an occasional glance at these types of beams will not harm your eyes.

By and large, the laser tools fall into two categories: rotating (also referred by makers as "rotary") and what we'll call "pointing" lasers since the more common "nonrotating" label doesn't do the trick for us.

Rotating lasers have been around the longest. As the name implies, a spinning mirror bounces the laser onto an adjacent surface. As the mirror spins, what would normally be one dot of light appears as a line.

Pointing devices aim a highly accurate point of light, and run the gamut from simple, torpedo levels that throw off just one beam to more elaborate models that use angled pieces of polished glass to break the beam into vertical and horizontal beams at precise right angles.

While we may be oversimplifying, rotating lasers come in handy when you need a continuous line of reference to complete your work. For orienting your work from one point to another for either vertical or horizontal reference, however, "point-to-point" lasers fill the bill.

A vertical beam can be used to establish a plumb line to the ceiling, for example, from the beam directed at layout marks on the floor.

Plumbing and mechanical contractor "Butch" Niesen, The Frank Niesen Co., Cincinnati, uses a point-to-point device to make relatively quick work out of installing pipe. "In many cases, we can put the device on the ground level of a commercial building, drill a hole in the ceiling above and have the laser shine through all the way through four floors without moving the device."

Niesen also uses a rotary laser that he finds ideal for determining elevation and slope, such as installing long expanses of drainage pipe.

When it comes to shopping around, you'll find an amazing assortment of devices to choose from. To begin with, you'll need to determine whether a rotating or pointing laser is best for you. Also, figure out whether you'll need a model that serves more than one purpose or one that specializes in one particular task. After you've made those decisions, keep the following functions in mind:

• Self-leveling Vs. Manual: Manual leveling devices typically include bubble vials and knobs to twist to ensure accuracy. On the other hand, self-leveling lasers do the job for you and usually in seconds. While the technology varies from manufacturer, self-leveling devices operate on the same principles that make the old-fashioned plumb bob work. For example, some models allow the laser to "swing" on a pendulum and let gravity do the rest. If the laser tilts past a certain tolerance range, some units simply shut off.

  Other manufacturers may use servo motors to constantly keep the tool level to either horizontal or vertical. Keep in mind that some self-leveling methods demand more from the batteries than other variations.

• Power Life: While we're on the subject of batteries, some models may be plugged in - although depending on the work you do, you may not have the convenience of an outlet. Some models allow users to switch between alkaline and ni-cad batteries. Obviously, all these power options make a difference in running without stopping for a recharge or popping in fresh batteries.

• Beam Accuracy: After ensuring a level benchmark, the accuracy of the beam is another variable worth comparing. Accuracy is generally given in sales literature as "I1/4 inch at 100 feet," i.e., that your alignment could be off as much as a 1/4 inch 100 feet away from the device. Changes in temperature as small as a 1/2 degree F could also affect the accuracy of the beam as well, but aren't likely to stray that far to affect the typical plumbing and piping job.

While we're on the subject of the beam, how bright and crisp the point or line of light you see may vary. While we've mentioned the federal government limits the radiation intensity, the quality of the optics the laser shines through is another matter. There won't be a way to determine this quality from sales literature; you'll have to let your eyes judge for themselves.

We've included some information on just a sampling of what's on the market.