The light is green. The ambulance has the siren turned on. At a junction, even if the light is green, an ambulance moving any direction (following traffic or against it) has the right way. Cars need to be aware of emergency vehicles operating on the road. It's just common sense to slow down at a traffic light no matter whether there is an ambulance or the traffic ahead is smooth, pushing you to speed ahead.

If this even gets to the courts, hospital wins as there is video evidence to prove the driver wrong.