With my DD (now 3) we used a simple lamp on timer switch since she was very young, sure it was before she turned one and would always go into room within 10mins of light being on and she learnt that light on meant we were coming in so if woke sooner would chatter to herself till light on then more vocal. We are doing the same with my DS (just turned 1) since about 6months as he is an early waker so again really try not to get him out of cot till light on (he isn't getting it yet!).
We have just upgraded to a gro clock with my DD as have been having disturbed nights with DS crying and DD having nightmares so she sometimes sleeps in then the light actually wakes her so trying gro clock as light isn't as bright. WE have also only just taken cot bed down to bed so didn't want a hot lamp on in room with her. I can hear her up and chatting in her room but touch wood (only been 2 weeks), she has stayed in her room till light on then comes out shouting 'my lights on, its time to get up'! Apart from one morning DS woke her at 6:20 and when we got up again at 6:45 her door was open and she was playing on landing quietly after saying needed a poo, I asked if her light was on and she said no, so laid her back and said must wait in room, surprisingly she did actually go wait in her room for the 10mins till light came on!! she got a smartie that morning!! She can open door and as yet we haven't had to put stairgate on it as she hasn't realized she can open it during the night and come out (sure that will happen soon!).
Just gutted DS wakes up bout 5:30-6 and wakes her if don't go in quick so trying not to reinforce waking, however, have resulted in just giving him dummy and walking out till a later time, however, not seeing improvements yet!!!
I defo think the light / time to get up thing is a brilliant but simple idea. The gro-clock on lowest brightness is however, quite bright at night so using as a nightlight at mo!!