For a laser, the theory is that you can put a laser grid against a wall or light up a room, and if something passes in front of it, it will block out sections of the grid. It is a great piece of equipment for detecting movement, shadows, or solid shapes moving in the room.
The first choice of color for your laser is green. Green is the most visible color of laser. They are “diode pumped solid state frequency-doubled”. The laser runs through a series of diode crystals and dielectric (insulating material or a very poor conductor of electric current) mirrors that pass through a resonant cavity. IR Radiation is then blocked by an infrared filter behind the mirror that eventually passes through a collimator lens (a device that narrows a beam of particles or waves). .
There are two options for using a laser. The first option is the popular laser pen, and the second option is a plug in laser device commonly used by DJs in night clubs. At CCPS investigations, we use the laser pen. When using a laser pen, you need to keep in mind that they were intended for star pointing, etc. They have no efficient way of cooling down. When using the laser pen for extended periods of time, (longer than the recommended 10 minutes), the laser begins to produce heat. The diodes in the laser pens are small, and there is no cooling system to stop the diodes from overheating and failing. When they begin to fail, some of the grid may start to fade, which can lead to false positives for the paranormal investigator. It is recommended that for every 10 minutes of continuous use, it will need to be turned off and cooled for 3-5 minutes.
There is no indicator on battery life for the laser pens. The only way to tell is when the beams begin to fade. When this happens, there can be a "twinkle" effect in your grid. Example, we all know that stars do not twinkle. It is the scintillation that causes them to appear to twinkle. This is from the light having to pass through thick layers of turbulent air. In the case of the laser pen, as a diode starts to die, or the battery starts to fade, the amount of energy being created for the laser has this same effect.
There are both pros and cons for using the laser pen.
The Pros are: small, lightweight, easy to transport, and cheap.
The Cons are: they are not meant for continuous use, diode overheating, short battery life, and false positives.
If you are an avid investigator, and don’t mind changing the battery often, or have to stop using your laser to allow it to cool down after an hour or so, then you should have no problem. For some investigators, this is more trouble that what it's worth.