Late 60's or early/mid 70's...
Sun goes dark... Astronaut (and robot?) flies to sun (moon?) and puts up these bright lights to keep earth lit... If I recall, he is then stranded there for rest of his life(?) sorry for being so vague, but it's all I can recall.

Doesn't really fit your description, but my first thought was Silent Running (http://www.tcm.com/tcmdb/title/4387/Silent-Running/)

Thanks Quinn... that seems close enough to poss be what I'm thinking of... checked your link... looks like a poss match (I was 5 when movie debuted so my recollection may be off)... Will hope to get my hands on a copy .
Thx again.

You're welcome. You can view the whole movie on YouTube. Hope it's what your looking for.