I have been browsing sims 2 pics on tumblr and can't help but notice some of them are so clear with this beautiful lighting effect. Is this a mod in the game? How is it done? They look amazing!

There's this mod that gives you custom post mod effect, is it the one you meant? Esotheria-Sims has pictures with it installed in their game here and also talks bit about how it works and is installed since the original upload is written half in Japanese. If that's too much for you (and/or your computer) there's also Maxis Match Lighting mod by dreadpirate.

Maybe you mean one of the effects left behind when witches do the "Beautificus Locus" spell? It's quite frequent on Tumblr.
You can see it here at 4:18 - https://www.youtube.com/watch?v=tqmeUcDypLU

I think the effect itself is also available as decoration here: http://www.modthesims.info/d/515886

(You do need Apartment Life for the spell and the effect mod to work)

The OP is looking for "god rays" - a flare effect similar to these pictures of sun rays coming out from behind a cloud.

http://esotheria-sims.tumblr.com/po...igans-yet#notes

Yes! Thank you Foxmanic and RoxEllen. I'll give it a try. Thank you also Simmer22, but that wasn't what I was looking for.

Thanks guys!

Oh yeah, there's also object by JD that gives you the rays and few other effects, picture here, the download link seems to go through some link shortener which my browser promptly blocked as harmful so just in case here's the direct download link. Just be warned, that object is pain in the ass to work with, I always grab it accidentally while I try to move something else and that's just so annoying >_<