It depends on where the glowstone is actually being placed in the path. I'm assuming it'll be down the center of the pathway though

Glowstone gives off a light level of 15 which decreases each space away from the block (so really only 14 blocks away from the actual block will be lit). Blocks directly diagonal are considered 2 blocks away since it takes 2 steps to get there.
Hostile mobs can spawn in light levels of 7 or less

Unless I'm misunderstanding something, for a path that's 5 blocks wide to be safe, you'd need a glowstone block in the middle line of the path, 11 of some other block (instead of 12 I think since you're taking into account it has to go one upwards also), another glowstone block, and so on.
So 11 spaces in between glowstone if it's being placed in the middle of the floor.

simple question, simple answer: press F7, and you will see red crosses at the places mobs can spawn.

Their is a such thing as Minecraft Wiki... Mobs can only spawn past around 7 blocks from common light sources. (Below Light Level 7, can be seen in F3). Glowstone and normal torches emit a light level of 15, so mobs can spawn 8 blocks away from that.