Both are line of sight - as in you have to be facing the set for the glasses to sync. Turn your head, sync gone. IR seems to work from greater distances. Can you disable the DLP Link on your set? IF not, I recommend DLP Link glasses. Most IR glasses will not correctly block the DLP Link signal and you'll have tinted blacks. The DLP Link glasses will block the flash and you'll get better black colors. DLP Link glasses usually have issues if there are other light sources near the TV. That is all that I can think of at the moment.