Increased light levels when light block next to block of amethyst

Light sources placed next to a block of amethyst give off a higher light level. Perhaps boost the light level by 4 units. If the brightness calculation were to go over light level 15, the illuminated blocks remain the same visually as if the light level were 15 to make it easier on the game engine. The end effect would be light levels would be 4 units higher radially from the light source then they currently are now. This would help with mob proofing the base a bit but not completely overpowering the issue of lighting when it comes to mobs spawning. Since amethyst is kind of expensive this would be good for end game. And it allows player to use less lighting elements to illuminate their area.