Sean Wammer

I can also confirm for 14w21b. Additionally powered redstone blocks act as transparent and exhibit this behavior. It seems that transparent blocks often do not update their light level, thus preserving previous sky light levels.

I've had this same problem with stained glass but am having trouble duplicating it.

I agree, but it is easier to demonstrate the redstone lamp opacity by pressing F3 and checking the sky light levels. If you create an enclosed space out of redstone lamps, you find the sky light to be 0. Then when you power the lamps, sky light gets in. I don't think this is intended behavior. But perhaps it is.

This bug makes it very difficult to enclose a daylight sensor with redstone lamps to make a lamp that turns itself on at night!