A green laser has more versatility, strength, and brightness than traditional red lasers. This color of laser can be produced in a small, handheld tool that looks like a miniature flashlight. Amateur astronomers often use a green laser because it reaches so far into the atmosphere, with a visible beam, that you can point out stars and galaxies.
Lasers are powerful lights where every wave, or piece, of light has been precisely lined up into a solid beam. Such light is said to be "collimated," or made into a column. Different colors of light, and lasers, are determined by the size of those tiny waves, called the wavelength. The popular red laser has a wavelength of 650 nanometers, that our eyes perceives in the visible spectrum as red. However, green light has even more energy in a wavelength of a minuscule 532 nanometers.
A green laser has several advantages over a red laser. First of all, green is closer to the center of the visible spectrum, so it's easier for our eyes to perceive the color at night. Since it has more energy, it can travel farther to project a small dot on low clouds and far off hillsides 9,000 feet away (2,740 m). The tool can form a visible beam even without fog or dust to exaggerate it. A green laser looks as much as 50 times brighter than the red equivalent.
During star parties, backyard astronomers using small telescopes prefer a green laser to point to particular constellations, galaxies, and stars because the beam reaches so far into the sky. A green laser is especially compatible because it doesn't interfere with dark adaptation, or how our eyes become more sensitive to dim light in persistent darkness. Astronomers opt for strengths around 5 milliwatts, which is a high powered laser. Yet machines that deliver fun laser light shows might use a much weaker strength, such as 1 milliwatt, to reduce the potential for harm.
The process of forming laser beams out of laser diodes is complicated. Special crystals must filter and focus the light to get it to the right wavelength and perfectly collimated. Red lasers use direct injection laser diodes, yet a green laser requires more steps so they are more expensive. Then again, the process can be more tightly controlled. Some models allow you to pulse the light, so it's released in spurts and makes a dotted line. Others let you focus the green laser, so the circle creates a tiny dot no matter the distance of the object on which it falls.
Using a green laser, just like a red laser, requires safety precautions. Even a quarter of a second exposure to your eyeball can permanently damage your retina. Never point a laser along the ground where it can encounter cars, people, or pets. Purchase a strength compatible with your intended usage, and don't let children play with lasers.