The Light Laser is the next defensive structure that most players will build. It’s used as fodder at all stages of the game, much like the Rocket Launcher, but is better in two ways. Light Lasers have a higher shield and attack strength than Rocket Launchers, and Cruisers do not have Rapid-Fire against Light Lasers (100 Light Lasers are sufficient to repel 20 Cruisers, while 100 Rocket Launchers will be demolished by 20 Cruisers because of Rapid-Fire).
The Light Lasers costs crystal in addition to metal, making the it 25% more expensive. It is also weak against Destroyers, while the Heavy Laser and Ion Cannon are not. Thus, due to their ‘balanced’ cost between Metal and Crystal, building Light Lasers is the best way to deploy a large amount of firepower and ‘fodder units’.
Note: For pros and cons of defensive structures, see Defense Comparison