Well the lightbox will work when the switch is turned on and the actual image your trying to view is below the max thresholds you set in lightbox settings. I use 1200 pixels personally. There is a catch 22 here. Lightbox can not handle images with dimensions over x amount of pixels. I like to say 1500 but it varies per install which is why you want to set a number lower than what dimensions will break it. Only testing can help you with that.