Tone's Shield System
TACTICAL DEFENSIVE DEFLECTOR SHIELD SYSTEM
The TDDSS is the main defensive system of most larger spaceships. The system is based on sets of deflector shield generators, which protect both the ship and it's contents from naturally occuring spatial and planetary hazards.
The deflector shield system works by creating a localised zone of highly focused spatial distortions, within which an energetic, gravitational field is maintained. The field itself is emitted, shaped and maintained by the shield generator - which in itself is actually four smaller generators, positioned around the craft - resulting in a field that surrounds the form of the spaceship itself.
The field is highly resistive to physical impact, ranging from relatively small subatomic particles travelling at high velocities, to much more massive bodies at lesser relative velocities. When such an intrusion into the field occurs, field energy is concentrated at the point of incursion, creating an intense localised spatial distortion. The net result being a semi-elastic collision with the 'shields'.
The shielding system is also effective against wider ranges of electromagnetic radiation, as well as nuclear and other radiated and field energies.
The shield system uses groups of four polarised gravitic field generators, whose output is phase synchronised with each other. The phase output frequency is modified randomly so as to prevent hostile forces gaining an advantage by adjusting and matching their directed energy weapon output frequency so as to penetrate the shields. (Too star trek? I dunno...)
Why lasers don't pass through (or why ordinary light isn't blocked):
The field of gravitons is just there, held in the deflector field by the generators. There's no need for sensors to do any work because the gravitons are polarised to such an extent that only highly focused, highly polarised light (or should I say LASERS) is affected by them. Since light from stars and such is not polarised, focused, or of high enough energy to cause damage to such an extent where the shields would deflect it, it simply passes through the deflector field.