Using a 1mW and 5mW laser pointer.

How long would it take to have temporary blindness?
How long would it take to have permanent vision loss?
How long would it take to have permanent blindness?

(No, I’m not planning on doing this. It’s for a school project, but I’d rather not find out by trial and error.)

Thank you in advance for anyone who may be able to help me out.

The hazards of laser pointers are limited to the eye. Although with most visible lasers, the largest concern is potential damage to the retina, most laser pointers are not likely to cause permanent retinal damage.

The most likely effects from exposure to viewing the beam from a laser pointer are afterimage, flash blindness and glare. Flash blindness is temporary vision impairment after viewing a bright light. This is similar to looking directly at a flashbulb when having a picture taken. The impairment may last several minutes. At night, when the pupil is most open, the effects would be magnified.

Afterimage is the perception of spots in the field of vision. This can be distracting and annoying, and may last several minutes, although there have been reports of afterimages lasting several days.

Glare is a reduction or complete loss of visibility in the central field of vision while being exposed to the direct or scattered beam. This is similar to viewing oncoming headlights on a dark night. Once the beam is out of the field of vision, the glare ceases. While this does not pose a hazard to the eye, it can cause serious distraction and outrage. Glare can be exacerbated when the beam is reflected from a mirror-like surface.

Several individuals have reported temporary blindness when targeted by a number of laser pointers. This is becoming more prevalent at sporting events. A few individuals complained of afterimages lasting several days.

A high school cheerleader reported being exposed at least three times. After the last episode, she reported first seeing "green", then experiencing partial vision loss, which lasted for several months. An ophthalmic exam found no retinal damage.

A standard laser pointer is limited to be under 5 mW of light power. The damage threshold for the human eye is about 1 mW. So, since 5 > 1, a laser pointer can damage your vision. However, your eye has some built in safety mechanisms. In particular, you have a reflex to blink and look away when you see a bright light. The time that it would take for a 5 mW laser to do damage is longer than the time it takes to blink. So you would likely blink before any permanent damage was done. That is why laser pointers are considered to be relatively safe: because your blink reflex will save you. However, if you suppress your blink reflex and stare into the laser, it can certainly damage your vision.

The reason laser pointers are not generally more powerful than 5 mW is because above 5 mW, the damage will occur faster than you can blink. So if you ever come across a laser pointer with more than 5 mW, you should be very careful (all laser pointers are labeled with their power).

Green laser pointers are usually infrared lasers that are double to green. However, if you have a cheap (and illegal) one, it may not have an infrared (IR) filter, so some IR light may leak out with the green. That is especially dangerous for two reasons. First, to get 5 mW of green, the laser will need to make more than 5 mW of IR. However, IR light can burn your eye just like visible light, so more than 5 mW of IR can and will do damage to your visions. Second, your blink reflex does not work for IR light because you can’t see it. So you could stare happily into an IR laser without even knowing it until your vision started to decrease. Now a legal green laser will have the filter that removes any left over IR light. So this is only an issue if you buy a cheap laser or if you are disassembling your laser pointer.