Lindsay Lohan

Steve Granitz/

Happy birthday, Lindsay!

LiLo hits the big 2-2 today, and she'll celebrate tonight with a private party at Teddy's at the Hollywood Roosevelt Hotel, sources exclusively tell me.

But gal-pal Samantha Ronson won't be mixing business with pleasure—DJ AM is spinning for the bash.

Crashers, be warned: The list at the door is going to be strictly enforced with no wiggle room. A source says, "It's gonna be on lockdown."