Roblox Bhop and Surf use the Shadowmap lighting technology. To use that in Studio, in the explorer window, navigate to Lighting. Click on it and look at the properties. The Technology property needs to be changed to Shadowmap.
Note: both ClockTime and GeographicLatitude are used to control the position of the sun
To change game.Lighting properties for your map, you need to add a script to your map model.
Example:
local l = game.Lighting
Assign a variable name to game.Lighting for ease of use, here we just use l
l.Ambient = Color3.fromRGB(100,100,100) l.ClockTime = 12 l.GeographicLatitude = 21
Increase the Ambient value to make shadows less dark so indoor areas have more visibility. Change the position of the sun so it is more directly overhead and creates less shadows.
For properties that use Color3 values, simply use Color3.fromRGB(R,G,B) and fill in the R,G,B with the corresponding red, blue, and green values of your choice. The others just use numbers.
Create a Sky object in studio and put it inside your map model. Follow the instructions on this Roblox Developer wiki article about custom skyboxes if you need help.
Next, put a script inside the Sky object. The script should say:
script.Parent.Parent = game.Lighting
All this does is change the parent of script.Parent (the Sky object) to game.Lighting. This just moves the Sky from your map model to game.Lighting where it belongs.
Finally, turn off the CelestialBodiesShown property of the Sky object if the skybox already has a sun, otherwise you will have two suns (the sun from the skybox images, and the sun added by Roblox).