I was testing out the new blocks in the snapshot in creative mode and I found that when I placed down a sea lantern next to some magma blocks and then destroyed the sea lantern, the light from the sea lantern would stay as if the sea lantern was still there and would not go away until all the magma blocks are removed/destroyed close to it. I have not tried any other light sources yet.
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SunCat
Dupe of MC-102162
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I found the same problem and was about to report it yea it happens with glowstone Jack o' Lanterns and other light sources such as torches. I don't know if it is a bug or if it is a secret feature like the more light around it the more it absorbs? Don't know but for now lets just mess around 😃
Might be a bug, might be WAI. The magma block basically absorbs the highest light level from the light source(s) surrounding it. So for instance with a torch (14 light level) the magma block will absorb 13 light levels (since it's one block away) and retain that light level indefinitely. It would be very useful if this was a official feature but we'll see what Mojang decides.