From what I understand... Glowstone, I believe, has a light level of 15. Each block away from the glowstone reduces the light level by one. Six blocks away would bring the light level down to 9. Most aggressive mobs spawn at a light level of 7 or less. You should be plenty good with your light levels.
You also have to count the height. Glowstone itself is light level 15. The light level reduces by 1 for each block you move away from the glowstone in ANY direction it is not obscurred by another block. So, if you imbed it in a ceiling at the 4th blocks off the floor, the block on the floor right below the glowstone would be at light level 12 (15-3), the blocks on the floor adjacent to that one in any direction would be at Level 11, etc. If you have glowstone lights spaced 6 apart, however, the light of each overlaps, so you should be good unless you put your lights 6 away from the wall first off. You should always start the row of light away from the wall and 1/2 the distance you put the lights apart from each other.
It depends on what you mean. If every sixth block is glowstone then you should be ok, just. If you have 6 non glowstone blocks between each one them you're not. Even in the case where you're ok, it's just barely, and you'll have to be very careful about building in the area, as any blocks that partially or completely block light could cause some blocks to drop below spawn threshold
im making a 4high 6far apart glowstone but need to know if mobs can still spawn within those dimensions
From what I understand... Glowstone, I believe, has a light level of 15. Each block away from the glowstone reduces the light level by one. Six blocks away would bring the light level down to 9. Most aggressive mobs spawn at a light level of 7 or less. You should be plenty good with your light levels.
You also have to count the height. Glowstone itself is light level 15. The light level reduces by 1 for each block you move away from the glowstone in ANY direction it is not obscurred by another block. So, if you imbed it in a ceiling at the 4th blocks off the floor, the block on the floor right below the glowstone would be at light level 12 (15-3), the blocks on the floor adjacent to that one in any direction would be at Level 11, etc. If you have glowstone lights spaced 6 apart, however, the light of each overlaps, so you should be good unless you put your lights 6 away from the wall first off. You should always start the row of light away from the wall and 1/2 the distance you put the lights apart from each other.
i have them 6 apart distance between each other going in one direction, and 4 high height off the floor, ive seen monsters still spawn
It depends on what you mean. If every sixth block is glowstone then you should be ok, just. If you have 6 non glowstone blocks between each one them you're not. Even in the case where you're ok, it's just barely, and you'll have to be very careful about building in the area, as any blocks that partially or completely block light could cause some blocks to drop below spawn threshold
http://minecraft.gamepedia.com/Light
This page will give you the info you need. Scroll down to the section on "Spread" and consult the chart to understand how lighting works in MC.