Laser Batteries are a point defence system, being clumps of many small blasters of intensified light. They're not very powerful, have a short effective range, and cannot penetrate defence screens, but the sheer volume of light blasts are great for intercepting barrages of missiles and fighter squadrons. Silversheen currently has six Laser Batteries, meaning it can target up to six missile barrages and/or fighter squadrons, which is a fair number for a ship this size.
Needle Beams are both an offensive and defensive system, being a single large blaster of intensified light. It is moderately powerful, has a decent range, and can penetrate several layers of defence screens, armour and hulls, but has a small surface area of effect. It is great for targeting specific systems on an enemy ship, but deals little damage overall. And since they can penetrate shields, they can take out torpedoes, which are large shielded missiles. Silversheen has two needle beams at the moment, which isn't very much.