R.
First of all, I just wanted to offer some reassurance that his behavior is normal. At 4 years old, the imagination has transitioned from pretend play (real life imitations, cooking like mom, playing doctor, etc) to fantasy play (fairies, dragons, etc) which also means monsters and things may seem very real and so can make bed time hard even though your child may not know how to tell you.
I will aslo say that I slept in a cot bed by my mothers bed until I was 5 years old because of this same issue. Having the light didn't help, if she stayed til I fell asleep I just woke up soon after and tried to get in bed with her.
Some advice I have read came out of a parenting book/philosophy called Love and Logic by Charles Fay. There's a video presentation of the book too. I checked it out through my son's school so you might ask your local school if they have it. Or, you can always just go to Barnes and Noble or something and read the section on what to do. I can't remember what their advice was, but I have used a lot of other techniques I learned and they work great!
Last thing, I let my husband do my kids bedtime routine because if I put them to bed it takes longer and they don't listen to me. (My 5 year old son and 1 year old daughter share a room right now and that seems to help them with being comforted. but my daughter likes to get up and sleep in the living room or some other strange place out of her bed). But, letting him do the bedtime routine cuts down on my stress and feeling frustrated.
Good luck!
R.