Laser Pointer

Wikipedia describes this as a small laser designed to highlight something of interest by projecting a small bright spot of colored light onto it.

This is exactly how it should be used primarily, to make something you are looking at stand out as in the night sky for astronomers or when you are out of doors and need to point to something in the distance. The lower strength is good for business or as a teaching tool for pointing in auditoriums.

There are quite a few different colored laser pointers available from red, red/orange/green/blue and yellow. Of these the green is the brightest.

The reason for this is that the human eye is most sensitive to the lower colors of the spectrum and green is one of those. Therefore it appears a huge amount brighter than the other colors. The green laser module will appear significantly brighter than the red of the same output.

There is another color now available blue/violet which is also another very bright beam.

A green laser pointer of 5mW strength with a wavelength of 533nm will be brighter than say a red 5mW at 640nM.

Output is measured also in nanometers [nm] as well as mW. A nanometer is defined as being a metric unit of length equal to one billionth of a meter.

30mW is regarded as astronomy and military grade of strength.

A 200mW green laser is visible for 80 miles.

A laser pointer can be expected, with sensible use, to have a life expentancy of more than 8,000 hours, that is the pen itself not the batteries of course.

Safety is a prime consideration when using a laser pointer. When these pointers were firsts introduced it was known that a 1mW power [class 2 laser] was quite safe because if you just blinked you gave your eyes enough protection. That is not to say that even this strength cannot produce retinal injury. If for some unknown reason a person overcame their natural tendency to blink and stared at the beam they could definitely bring about some sight damage.

If you were looking directly at a laser beam which was a mile away it would appear to you as though you were looking at a 100W bulb which was only 100 feet away. That would not be comfortable and I would think that normally a person would blink or turn their eyes away from such a bright light. This you need to for the safety of your eyes.