How can I tastefully lighten wood beams on ceiling?

I would consider a white wash effect.

I agree with Janet! White washing them would lighten them up, but not cover the grain. Load a brush with paint, dab the paint off on some newspaper and gently brush the beams in a dry brush effect.

Great idea! Thank you all.

I would do just the opposite. Pickle or white wash them with a thinly watered down paint, letting dry and repeating until you get the effect you like, Do not use dry brush, you likely will get spotty over load pigment that will look splotchy.

You can try this whitewashing technique: http://www.hometalk.com/diy/-7077993

I had some of the ugliest fake beams I've ever seen in the master bedroom of the 100 year old house I bought a few years ago. I wanted them down in the worst way, however I realized that if I did I would have to replace the Sheetrock on the ceiling and all of the crown molding. Wasn't going to happen. Between the beams the ceiling was painted tan---ugh. So, I reluctantly began painting the ceiling white. As I painted I also painted the beams and lightly wiped with a wet cloth as they were being painted. I actually like them now! They aren't so obvious and ugly, just a great asset to the ceiling. I took down the ceiling fan and put up a crystal waterfall chandelier. Ceiling is now really pretty. I can send pics if you'd like.

I'd love to see your pictures! I've been thinking that painting was the only way to go since they are so, so, so dark. Please post!