Can a pocket laser damage our eyesight? The answer to this question depends on many factors. It is a bit like trying to establish a single safe speed for driving a car. Under normal conditions, a speed of 30 mph is safe, but not during storm or heavy fog. It is similar with defining the safety limit for the laser pointer. The likelihood of eye damage depends on many factors. It includes the laser color, divergence (beam dispersion), distance from the source, the time our eyes are exposed to it and, above all, power. It is the power that is the main determinant of marketability. Depending on the country there are different standards (with divisions into special classes), but generally lasers up to 5 mW are considered to be the upper safe limit. In the United States the limit is 3.5mW.
The power of lasers is given in milliwatts (mW). Theoretically, 3.5 mW is a safe value because it represents about one-tenth of the actual damage threshold, but history records cases of permanent vision damage from a pocket laser. Why? First, there are cheap Chinese products on the market the power of which may differ from that declared on the housing. Second, users of the laser may be children. In 2018, a 9-year-old became blind in one eye by looking into a green laser beam several times.
Why worry about 5 mW at all? After all, it’s only 5 thousandths of a watt, or less than one percent of one percent of the power of a 60-watt light bulb. The reasons are two. First, a light bulb converts only about 10 percent of that energy into light (the figure is different for an energy-saving bulb). Second, the bulb shines in all directions, thus we see only a small portion of the light it emits. We reduce this amount even further by moving away from it. A laser emits light in one small focused beam.
Despite meeting safety requirements, small lasers can still be dangerous. The reason for this is known as flash blindness. Everyone knows the feeling of temporary blindness after a camera flash or after moving from a dark to a bright room. A laser beam can lead to such temporary blindness, which can have extremely severe consequences for e.g. drivers, or machine operators. There are known cases of attempts to blind airplane pilots. The effect is particularly strong at night, when pupils are dilated. Lasers are also used during protests and riots. They are used to damage drones, CCTV cameras and to blind police. IR (infrared) and UV (ultraviolet) lasers are particularly dangerous. Normally the eye exposed to a laser should blink in reflex, but UV and IR rays our body is not able to detect. Recently, lasers were used in the riots following the death of George Floyd. Three officers were blinded by lasers (authorities report that permanently).
Regardless of the power, lasers should be used with caution and under no circumstances should a child be allowed to play with them.