Compared to the Heavy Needler, the Light Needler has the same dps/OP and same efficiency, same armor penetration, 700 range instead of 800, and a faster firing cycle (a bit less alpha). If larger mounts are supposed to be slightly better on an OP basis, then this is fine. The main difference is 100 range, which I wouldn't mind seeing a single OP deduction for.
Compared to the Heavy Needler, a railgun has 43% better damage per OP, twice the armor penetration, 700 range instead of 800, and .9 instead of .8 efficiency (12.5% more flux per damage). It is more accurate, though needlers are already accurate enough that it doesn't make too big a difference, but much less alpha. I think this is a bit too good.
Compared to the Heavy Needler, a Heavy Autocannon has 28% more damage per OP, twice the armor penetration, the same range, 1.0 efficiency instead of .8 (25% more flux to per damage). As they are the same mount type: HAC's have 86% the DPS of Heavy Needlers per mount. But it also has much lower accuracy, so both the DPS and efficiency go down vs targets smaller than cruisers (smaller than destroyers with skills). This is an easier comparison as they take the same slot, and people have done a lot of A/B testing: Heavy Needlers are significantly better. In practice they do much more than the DPS difference would suggest due to accuracy and alpha.
I would support both light needlers and railguns being 8 OP - railguns are higher damage light multipurpose, while light needlers are higher efficiency pure anti-shield.