First of all... what is Sunlight Bulb?
Well... Sunlight Bulb is used to plat Steed Seed and Steed Seed is used to make a lot of mounts as you can see the images below:
Ok, now that you understand what is Sunlight Bulb... you can now know where it drop/spaw.
Every uber/adventure world can drop Sunlight Bulb! You just need to know this:
Biome: Peaceful Hills
If you don't understand what I said above. Find this icon:
When you find Peaceful Hills, make sure to be looking to the sky to sight this big and weird contruction of a plant.
when you find this big plant, go over there and should be like this:
MAKE SURE TO SEARCH EVERY PLACE NEAR THE PLANT, you also can go trought cave below the plant and find this
That's it. If you liked what you read here PLEASE, hit that LIKE button and Favorite too. Share with your friends and trought the trove community. It may help a lot.
Credits: Guide by JohnzBallad- http://steamcommunity.com/sharedfiles/filedetails/?id=482972389