the sun is far far away, but there is NO better source of light than the sun...
just keep burying the plant a little deeper. seedlings always stretch way faster than they veg, so every few days, i have to bury them another few inches [i put the leaves about one inch from soil]
the way i see it, if i'm right anyway, is that the stem being buried like that could make room for more possible root sites, and hence bigger plants..