As the lighting system has been changed to calculate light emitted based on the volume of block, small amounts of glowstone or other light emitting blocks no longer emit a useful amount of light. A config option would be useful so players can choose to revert to the previous behaviour, so builds such as lamps using small amounts of glowstone to emit light would still work.

MC1.12.2
Little Tiles 1.5.0

Nevermind, didn't realise that recipes could be crafted as a light structure to achieve this same behaviour.