Rescuers say the light from an iPad guided them to a day tramper who went missing in Fiordland National Park.
The 66-year-old English tourist lost the track during a walk with his wife in the Lake Marion area, off Hollyford Rd, on Wednesday.
The couple had arrived at the Alpine Lake together at 1.45pm but parted ways about 3pm, when the husband began the descent back to the car park about 15 minutes before his wife.
When his wife could not find him she searched the track twice before raising the alarm at Gunns Camp about 7.30pm.
Police said the man had a pre-existing heart condition and a search and rescue response was launched immediately.
The Gunns Camp manager and two local hunters began searching the track about 8pm while a search and rescue team from Te Anau was assembled.
A Southern Lakes helicopter equipped with night vision and thermal imaging equipment joined the search shortly after 10pm.
The man was spotted after they saw a light in the Marion Creek bed area, off the track.
He had been carrying a camera and an iPad, which provided enough light to be detected quickly in the darkness.
The man was in good health and was flown to Gunns Camp, where he was reunited with his wife about midnight.
Police stressed the importance of carrying a light source outdoors, no matter how insignificant a tramp may seem to be.
The track the tourist became lost on is regularly used by day walkers en route to Milford Sound and the surrounding area.
About 50 people a day use the track at this time of year.