The Light domain was a set of spells that were granted by deities whose portfolio included the aspect of light. Clerics who chose this domain were granted free access to these spells (they could cast them at any time without having to prepare them in advance).
Novice Light domain clerics could cast burning hands, faerie fire, flaming sphere, and scorching ray. Experienced casters could cast daylight, fireball, guardian of faith, and wall of fire. The most powerful of these clerics were able to cast the mighty flame strike, and gain the ability to scry.