Build the redstone block clock from MC-5774. You will notice the pistons are powered but the redstone dust doesn't look powered. Attaching repeaters/lamps to the dust as shown in the screenshot will retrieve power from the dust.
The dust should look powered when it is. Also, this clock is extremely fast, if it is too fast for the redstone dust to power on, it probably should be slowed down.
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Applies to powered redstone aswell which does not change, see MC-5935.
confirmed, seen in cubehamsters video http://youtu.be/gAAoKMU6dBw
Also note that whey you are using comparators instead of repeaters, they seem to repeat only the visible redstone state. So if you replace the repeaters on the screenshot with comparators, the lamps will not light up as long as the wire looks unpowered. Even a repeater or something else behind the comparator will fail to receive any power at all.
Thanks for the update.