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

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.