I saw a 40k player use these and just had to do my own.
They are really easy to make as well.
LED tea lights (so they flicker)
cotton balls (4 or 5 per tea light)
hot glue gun and glue sticks
flat black spray paint
How to
1. Gently pull cotton into a larger "blob"
2.Glue to Tea Light base.
3.Lightly glue cotton balls together
4. Let cool
5. Spray paint to desired tint. I went with random darker patches.