i am 3 weeks into bud and things r well on the way. but when i put my hand into the plants at mid height there is little or almost no light penetration through to lower bud. can i cut off some high larger/older leaves to help light get to lower bud.
No. Strip all the little stuff off the bottom. You should only have clean branches where your sun isn't shining so all growth potential goes to the flowers and leaves that are absorbing all the light. 21 days is a good general time to do this. The buds have already started forming and you have a really good idea of what's going to be in the light. Trim off the leaves and stems of any tiny skinny shoots and buds that get little to no light.
You can try to tuck or tie off leaves and branches to place them where you want, to allow more light penetration.
I've done that too, Toasty and I've found that the less you mess with the leaves and bud, the more yield you get out of the trim. It's apparently pretty easy to damage trichomes. I've found that once the canopy develops, the scrap down where it's dimmer light never develops the full medicinal value that the buds exposed to full lighting get. I essentially cut out every budsite that doesn't stand a chance of growing up, out of the canopy and leaving the leaves. If you do this right about the time the stretch is stopping (approx 21 days, depending on the strain) there really isn't much stress to the plant and it pushes all of the remaining flowering energy into the top buds. Don't get me wrong, I like trim but it's just not the same medically for me and I get the same yield, if not better. Only all bud.