Light Arrow

The Light Arrow gives you're bow the Power of Light. They are twice as powerful as the Ice and Fire Arrows, but they require twice as much magic to use.

Ocarina of Time
Princess Zelda give them to you in the Temple of Time, they are the final weapon needed to take on Ganondorf.

Majora's Mask
They are found in Stone Tower Temple. They are used to turn the Stone Tower Temple upside-down.

The Wind Waker
Link finds them in Ganon's Tower by fighting Phantom Ganon. They are also used to defeat Ganon.

The Minish Cap
They are achieved after a few steps in a mini-quest, and are optional. Kinstone fuse with someone who looks like he's not from around here in a house in western Hyrule Town early in the game. Go to the newly opened portal, and use the Gust Jar to suck in the ghost circling the old man. Return later in the game, and talk to the man. You'll get the Light Arrows then.