Minecraft Mob Generator?

I have a drop tower mob grinder for my MineCraft survival mode. and basically what that is, is a tall enough room that if you drop down it will kill you on impact. at the top of the room is a pitch black room with a hole in the middle and four water streams leading to the hole. since mobs like creepers and spiders spawn in the dark, they will spawn up there and eventually wonder into the stream and take them into the hole so they will fall to their death so i can collect their droppings. i got it working fine and i have no problems. i was wondering if the same would work just the same for mobs like pigs and sheep. like instead of a dark room, i could make it the brightest room ever. don't monsters spawn in the light? and when they drop do they leave droppings or can you only get them when you kill them with a sword? thanks :)