To U.S. pilots who are accustomed to stobes on when entering the rwy and then landing lights on to signify when T/O clearance is received, be advised that most overseas operators don't use this "Landing light = on the T/O roll" system to communicate to others down the runway they are moving. Most overseas operators swith on all lights when cleared to line up and wait, including the landing lights, the same way they do when cleared for T/O. This can be disconcerting for those who are be used to the other system and may be crossing the same runway downfield. The initial thought is that aircraft is rolling, clearance or not.
To those who aren't used to what now is pretty much standard in the U.S., this Landing light = T/O clearance was recommended because studies done during a focus on runway incursions/accidents found that the wash of landing lights from a stationary aircraft sitting on the runway really doesn't make it much more visible to landing aircraft behind and above, the strobes do. On the other hand, the landing light is brightly visible down the runway to the pilot sitting on the ground in another aircraft who may or may not have been given a crossing clearance, and the movement (wiggling) of the light from that vantage point as it rolls easily noticed. Switching the landing light on with T/O clearance is also a visual signal to the tower that the correct aircraft is responding to the T/O clearance over the radio.
Much like the taxi light is used to communicate movement on the ground (On when moving, OFF when stationary), the landing light is used to signal movement/actually Taking off.