Light Arrow

The Light Arrow gives Link's bow the Power of Light. Each arrow uses Magic Power. They are presumable based off of the Silver Arrow from the previous 2-D games, as they share a similar name and function.

Ocarina of Time
In Ocarina of Time, Princess Zelda entrusts Link with the Light Arrows in the Temple of Time. They are needed to defeat the King of Evil, Ganondorf, and are useful in stunning the final boss, Ganon. An added bonus is the almost guaranteed side effect of any enemy killed by them dropping fifty Rupees.

Majora's Mask
In Majora's Mask, they are found in Stone Tower Temple, and are used to invert Stone Tower Temple in order to continue through the dungeon. Also, if Link defeats an enemy with a Light Arrow, 50 Rupees are automatically rewarded. They are nearly identical to those from Ocarina of Time, but are more powerful against enemies, and are even able to damage fully armored Iron Knuckles.

The Wind Waker
In The Wind Waker, Link finds them in Ganon's Tower by completing the Illusionary Room puzzle and fighting Phantom Ganon. They are used to kill Phantom Ganon, destroy Puppet Ganon, and defeat Ganondorf. They are the ultimate weapon in the game; it performs a one-hit kill on anything (other than bosses), even if it is wearing armor, as is the case with Darknuts. However, like in Ocarina of Time and Majora's Mask, they use Magic Power.

The Minish Cap
In The Minish Cap, they are achieved after a few steps in a mini-quest, and are optional. Kinstone fuse with the man from the Wind Tribe living 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 Gregal. Return later in the game, and talk to him. You will then receive the Light Arrows as a present for saving his life. Holding the arrow in the bow will charge up the Light Arrow; if the Light Arrows aren't charged, they will act as normal arrows. If you haven not saved Gregal by the time you reach Cloud Tops, he will have died and the Light arrows will be impossible to obtain.

Twilight Princess
In Twilight Princess, you cannot actually obtain the Light Arrows. However, they do make an appearance. In the battle on horseback with Ganondorf, Princess Zelda will fire Light Arrows at him to slow him down, and then you can attack him. They are granted to Zelda by the four Light Spirits.