Light spells (continual or otherwise) are not uncommon. I don't know about you, but as soon as my players have the chance, they ditch most of their torches and lanterns for "Continual Light Sticks." I can't say as I blame them. It certainly is less encumbrance and book-keeping. I've previously mentioned in passing how I consider CL a world-changing spell. Or at least, it would be if carried to its logical conclusion.
I didn't want to talk about Continual Light today, though. I wanted to talk about how insanely powerful the plain old 1st level Light spell is in combat. It's to the point where it's the only spell a low-level cleric might consider to replace Cure Light Wounds on their prepared spells (though that's unlikely).
Why is it such a powerful spell? Take a look at the spell description (from Moldvay):
Light Level: 1
Duration: 12 Turns
This spell casts light in a circle, 30' in diameter. It is bright enough to read by, but not equal to full daylight. It may be cast on an object. The light may be cast at a creature's eyes. The creature may make a saving throw, but if it fails, the victim will be blinded for 12 turns. In the D&D BASIC rules, a blinded creature may not attack.(emphasis mine)
So, you've got a 1st level spell with a 120' range (120 yards outdoors!), where a failed save vs. spells means most targets are basically out of the fight and practically helpless. In my campaigns, the player with clerics –lacking offensive spells like Sleep or Magic Missile– absolutely LOVE this spell.
The best part is when the PCs cut off the head and use it as a light source until the spell fades!