Say you drilled a hole down to the magma layer. Hot lava emits light. From what I've seen lava is red(?) hot. Then if you put some fibre optic cables down into the magma layer maybe protected at the bottom with a diamond layer to protect them from melting. Could you capture that light and bring it to the surface, in order to provide things like indoor lighting or even convert the light to electricity using solar panels?
(There is a place in Iceland where they are attempting to drill down to the magma).
What colour would the light be?