What has his diet been for the last few days? Mostly earth worms / Night crawlers?
If so this is normal.

earth worms / Night crawlers are like laxatives.

When I fed my little one mostly crickets and Dubia in the enclosure his BM was very well formed and mostly eco earth.
Now that I feed mostly Night Crawlers he is loose as a goose but much more stinky

About the light I think it is fine but the real test is the actual temp at night it shouldn't fall below 75F.