The air ambulance service covering Kent, Surrey and East and West Sussex has been given the go-ahead to operate 24 hours a day.
Waverley council has given planning permission for the aircraft based at Dunsfold Aerodrome to operate at night.
Some residents opposed the plan because of fears of noise and light pollution.
Chief executive of the air ambulance service Adrian Bell said he expected between one and four callouts across the four counties per night.
He said the service would also use a very quiet aircraft and lighting would be kept to what was needed.
Mr Bell said nothing would happen in the immediate future because there was a lot of work to do and night flights would come into operation over the next three to five years.
He said helicopters sometimes had to land in "very tricky places" by day and it would be more difficult at night, so the service had to develop its capability in order to operate safely.
"It's very important to understand how often we will be operating when we get to full capability," he added.
"At night, looking at the statistics for the sort of trauma events we go to, I would expect across the four counties about one, or two to four callouts.
"That involves in the vicinity of the airfield, about five minutes out, five minutes back, in what is a very quiet aircraft, with lighting kept to what is needed at the time to do it. I would be surprised if local residents found it that much of a disturbance."
Previously, the emergency helicopter at Dunsfold was limited to daytime and early evening flights.
The air ambulance service operates helicopters from Marden in Kent and Dunsfold in Surrey.