Laser Tag Beams and Sensors

Dispite the name, laser tag does not use a LASER (Light Amplification by Stimulated Emission of Radiation). The Tagger uses a light emiting diode (LED), which emits light in the Near Infra Red (NIR) region of the spectrum. In fact the LED is very simular to the device used in a standard TV Remote channel changer. While both laser diodes and LED's are semiconductor devices, they differ in the intensity of light generated and divergency of the light from the source. A laser diode beam is very intense and does not spread out appreciably over distance, it remains a tight cylinder. The LED beam, on the other hand,  has a large divergence angle and needs a lens to keep it focused. Over distance it spreads out like a cone (or more correctly a series of 3 cones formed from the different energy lobes), losing intensity. Laser can cause eye damage, even at great distances, because of the very intense focused light. LED's are harmless to the eye, due to the low power density generated even on lensed systems.

figure 1.  IR Beam is eye safe and effectivly covers the same body area at various distances,

 The Taggers used at a TagParty^TM  have the sensors mounted on them. There are no additional sensors worn on the body or head, and there is really no need. The spread of the IR beam means that if you hit the tagger you would have hit a sensor worn on the head or body (see figure 1).  The beam profile effectivly gives you the same target area at various distances, it is however harder to hit the target the further away it is (again see figure 1).

The only real argument for head or body mounted sensors is to stop a player from stand up behind, or peaking around, a barrier to determine other players positions without exposing their Tagger. To minimize this at a TagParty^TM  we use infrared reflective vests and eyeware. The IR beam can reflect off the IR reflective Safety Glasses and/or Vest and tag the sensor. While not 100% effective, testing has shown that tags are successfully registered on the tagger greater than 60% of the time. So keep your head down and get your body behind the barrier.

figure 2. Reflection onto tagger sensor