If you have already beaten the game you can not get the Light Arrows. First you need to go to Hyrule Town, and go to the North West part of town, and you will see a house with a yellow roof. Go into it and Fuse Kinstones with the man. It will unlock a teleport to the Castle in the Cloud Tops. In the castle you will find an Old man Plagued by an evil spirit, use the gust jar to suck it up. When you come back to the Cloud Tops later in the game, go to the old man to get the Light Arrows!