Minecraft – How to light megastructures in Minecraft without torch orglowstone spam

A light source illuminates a diamond (it doesn't "travel" diagonally).

Light does spread around corners, but does not travel through most solid objects. A torch placed on a pillar will provide light on the opposite side, but the light has to travel around the piller. The open space immediately adjacent to the piller and opposite the torch, is 2 spaces away, but takes the light 4 spaces to go around the piller. Therefore, from a starting light level of 14 at the torch, the open space will have a light level of 10, in the abscence of another source of light.

First, take note of some information about light-emitting blocks from the Minecraft wiki:

• Torches have a light level of 14, while glowstone has a slightly higher light level of 15.
• The light emitted decreases by one for each square of distance from the light source.

This means that if you wanted to light up a horizontal line of blocks such that the light level was 8 or higher everywhere on the line (to prevent most hostile mob spawning), you could place torches along the line with 12 blocks between them, or glowstone blocks along the line with 14 blocks between them.

Now, moving vertically will decrease the amount of light as well, also by one for each block moved. This would mean that if you moved 3 blocks horizontally, then 3 blocks vertically from a torch, the light level will drop by 6 to a value of 8. So, you could just count the number of blocks you have moved both horizontally and vertically from a source to figure out what the light level has dropped to and when you need to place another light source. I believe once you reach a count of N-1 blocks from the light source (where N is the light level of the source) is when you should place another one.

A potentially easier alternative to counting is to use the debug screen (press F3) to track light levels. This will show you a bunch of stats, like so:

The number to pay attention to is the one I circled labeled "bl", which stands for block light. This is the light level due to sources other than the sun and the moon as measured at your head level. This means that if you place a torch on the ground, then stand in the same spot, you will get bl = 13, since your head is one block above the light source.

Using this may make it easier for you to lay out your light sources and to check where you may have some dark spots. I use it often inside my structures to make sure I have lit them up appropriately.