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Since torches prevent mobs from spawning, is it possible to place enough torches within a specific radius to ensure safety during the night? I'm thinking of a situation without any shelter built, more along the lines of a flat plain. If it is possible, how many torches/how far out do I need to go to make that area safe?

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See also this related question (and answers): gaming.stackexchange.com/questions/15959/… –  Denilson Sá Jul 29 '12 at 2:17
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4 Answers

up vote 47 down vote accepted
  1. Learn about light:

    • Sunlight gives 15 luminance to the blocks it hits directly, or through half steps.
    • Lava gives 15 luminance.
    • Lightstone gives 15 luminance.
    • A jack-o-lantern gives 15 luminance.
    • A candle gives 14 luminance to the otherwise empty block it occupies.
    • A redstone candle gives 7 luminance to the otherwise empty block it occupies.
    • Every tile that isn't a light source has a luminance of one minus the luminance of its neighbors. For example, if you had a 6 and a 4 luminance sources close to each other, attached to a wall, you'd have this distribution:

                  1
                 121
            1   12321
           121 1234321
          1232123454321
         123432345654321
          12┴─────┴4321
           1     12321
                  121
                   1  
      

      ...except this works in three dimensions instead of two!

  2. Learn about spawning:

    1. The following applies to any difficulty, except for Easy.
    2. Every tile within 24 distance of the player is not eligible.
    3. Every tile outside a 144×144 square centered on you is not eligible.
      • Every non-glass, non-half step surface in the outer world with 7 or less luminance is eligible for spawning.
      • Every non-glass, non-half step surface in the Nether is eligible for spawning.
    4. Mob spawners cause mob to spawn at a high rate in any surface within 5 distance of it.

  3. In practice:

    Here's what I try to do to ensure a luminance of 7 consistently along a line:

    1. Place the first torch. Pardon my hexadecimal one-sided luminance graph:

      EDCBA98765432100000000000000000
      ↑
      
    2. Proceed until you find two tiles looking exactly like the next, then go back one.

      EDCBA98765432100000000000000000
                   ↑
      
    3. Plant a torch there. Lo and behold, minimum luminance there will be 8!

      EDCBA9889ABCDEDCBA98765432100
                   ↑
      
    4. GOTO 1

    You can adapt this algorithm to your necessities with ease. Just plant a torch in the darkest area when in doubt. (Duh.)

    Also:

    • Put torches directly onto surfaces for best results.
    • In your mining, be aware that any surface is good enough to spawn...

      ↓↓↓ ↓↓    All positions marked with an arrow are valid
      ███ ██↓   spawning points, to the best of my knowledge,
      █     █↓  and they all can lead to the just spawned mob
      █      █  to reach you.
      █     ↓█
      █↓↓↓↓↓█   Be vigilant and don't mine caves from the
      ███████   bottom up :(
      
  4. Learn how to keep mob that has spawned outside: make traps.

    • Mobs can only jump up one tile. Make pits deeper than that and, once in, they will be trapped (skeletons are still dangerous and spiders can climb out).
    • Mobs cannot deconstruct. Make walls. (Be aware creepers do explode, if they get close enough.) Use cobblestone: they have high explosion resistance and can't catch fire.
    • Mobs cannot use items. Protect your entrance with a wooden door. Plant it from the outside, or skeletons will be able to hurt you with their arrows!
    • Mobs' path finding is somewhat dumb. Protect your spawn point with water and liberal amounts of cactus (arrange them in a chequered pattern.)
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The algorithm gives you the least amount of torches you can possibly use to get 8 minimum luminance in a row. That's the bare minimum, and it is useful to know: anything more than that will keep you safe. –  badp Dec 8 '10 at 22:44
    
I'm interested in what you said about glass and half-steps -- if I build a fortress out of these two materials, I'll be spawn-free even if I miss a torch or two? Also, does that only count half-steps that make a half-block-high surface, or can I stack two half-steps for a clean white floor (or as the step between a half step and a block+half-step step) and remain mob-free? –  PeterL Dec 10 '10 at 1:49
    
One question, just to confirm - so light from two sources is not additive? I would have thought that the light next to the "4" square would also be "4", from 3 + 1 from the "6". –  Cyclops Dec 29 '10 at 20:17
1  
@badp, ah, yes, actually, light is additive in the real world :) Also, trains can reach velocities higher than 8 m/s, and leave piles, sadly, do not instantly decay. :) –  Cyclops Dec 30 '10 at 16:02
2  
@cyclops Light is additive in frequency certainly. If you wish to discuss this any further may I suggest physics.stackexchange.com? I unfortunately lack formal education in optics, or human perception thereof ;) –  badp Dec 30 '10 at 16:37
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Torches Provide a light level of 14. Note that this is to the block that they are in. Adjacent blocks have a light level of 13. Mobs require a light level of 7 or less to spawn. This means that mobs can't spawn within 7 of a lit torch. So placing a torch every thirteen tiles will keep a hallway lit.

T____________T
01234567890123   

You can expand this to two dimensions by placing a second line of torches 7 to one side and offset by seven.

T____________T______
____________________
____________________
____________________
____________________
____________________
______T____________T

See this post

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First, some mob spawning science:

  • Spawns occur in a 144x144 square around you (assuming a perfectly flat surface), but not within a 24 block radius of you.
  • Hostile mobs spawn at light = 7 or less
  • A torch provides 14 light to adjacent blocks and one less light per block of distance.

Using these measurements, it looks like you would have to make a grid of torches 13 squares apart that covers a 144x144 block area (excepting the no spawn circle around you, if you like).

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Mobs will spawn in areas of light 7 or lower. Source

Torches provide a light of 14, with the light value being reduced by 1 for every tile away.

14   13   12   11   10    9    8    9   10   11   12   13   14

Consider the line of light values above. The 14's are torches. If you put the torches no more than 12 squares away, you will prevent any monster from spawning in a straight line; do note however, that if you go with a strictly grid based system, you will have dark "centers" made from the torch squares. I recommend a staggered grid, each line "shifted" 6 squares from the other, so that the light values prevent the centers from getting to dark.

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I'm looking for a way to make sure that no mobs will exist anywhere in my vicinity by just using torches. If I just stand still with a circle of torches with a radius of 11, will it prevent mobs from walking into the area, or to an extent towards me? –  Nick H Dec 8 '10 at 21:10
3  
@Nick - No. Light (aside from sunlight) only affects mob spawning. Once the mob spawns, it can happily move into the light. You have to prevent spawning in the first place. –  sjohnston Dec 8 '10 at 21:21
    
@Nick - I misread your question. I apologize. Fallacious comment retracted. –  Raven Dreamer Dec 8 '10 at 21:39
    
no problem. I'm having trouble phrasing things today, so it's more likely to be my fault. –  Nick H Dec 8 '10 at 21:45
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