How light strike works?
It is similar to Laser Tag, which I understand, because you must be in
  dark place and you "shoot" laser beams. But how come that Light Strike
  doesn't shoot direct light. Is it some radio wave?


James Clerk Maxwell in the 1800s basically proved that light and radio waves are exactly the same thing. Just thought I'd get that out of the way first.

More than likely it uses a low power infra red (invisible) laser and the laser will be modulated with a signal that makes it instantly recognizable from changes in ambient lighting conditions.

Using a laser ensures a tight beam is "fired" at the target.

The sensor(s) will be an IR detector (likely) with an amplifier and decoder (for the modulation) and upon decoding the signal it will advance points on some scoreboard or other.