They are no where near as efficient as cruiser lasers but if you want to knock down cruiser shields without using the powerful cruiser laser then these might have the shield penetration and tracking you need to knock down the enemy shields so your beam lasers can cut into there armor.
The light plasma launcher is also reasonably cheap, which is why an awful lot of my cruisers are loaded for bear with light plasma. That’s right, I said it, I’m a cheap bastard.
I’ve never had very good success with plasma weaponry. I’ve always found it easier to have a line of missile spammers behind my beam cruisers.
I have to use more ships if I use it in place of cruiser lasers but they are a decent alternative for taking down shields. But generally I had better luck with missile heavy fleets as opposed to plasma heavy fleets.
the main problem i have with plasma is, that it misses too often against fast moving targets.
the light cruiser plasma has slightly better tracking speed than the cruiser laser (and better range), but the cruiser laser counters this with better fire interval.
since i like building very fast ships, i often see even my cruisers escaping plasma spam, the few shots that hit are negated by fast recharge shields.
Small plasma torpedoes never work for me. They don’t have that great of range and seem to never do much damage before getting totally killed.
It’s not that they are better or anything, its just a alternative if you don’t want to use the most powerful weapon in the game. if used in this fashion its not really a weapon you could massively underbudget your fleet with and expect to to win, at least not like the cruiser laser can.