Underground light: skystone

It's extremely hard to fully light a cave, so i propose to add a block that simulate sky light. It will propagate light downward, whatever the distance, like would do the sky. On the same time, the block could allow underground mechanisms that requires sky light, like zombie daylight burning or villages.

In the following image, i tried to fully light an huge room. As you can see, despites of the huge use of glowstone, it's still dark.

To explain that differently, the block would act as if you dig a hole straight upward to the sky. Some variations of this block could then be designed: one could emit light with respect to the day time, one could always emit maximum light, or using an inverse daylight logic.

I think that would be a very powerfull and endgame block, eventualy with ram issues. This could be very fun to use in creative, but also in survival, allowing smoother use of light.