A celebrity scientist has suffered blinding headaches after sealing himself in an airtight foliage filled chamber in a harrowing test designed to show the power of plants.
Professor Iain Stewart revealed the side effects after spending two days locked inside the see-through container for an experiment linked to a new BBC2 series.
The TV presenter and geologist is fronting the first programme in the channel's How Plants Made The World series.
He clambered into the transparent box, which was situated at the Eden Project in St Austell, Cornwall, on Thursday night and stayed there until Saturday night.
"I went into the chamber at 10pm on Thursday night and immediately what we did was take the oxygen levels from 21%, which is normal, to 12.5%," Prof Stewart told BBC Radio Five Live.
"Then a whole bank of lights were turned on and the plants inside the chamber started to synthesise and they started pumping out oxygen for me to breathe.
"I of course then needed to breathe to give them the carbon dioxide they needed as well. Everything was air sealed and the big question was whether the oxygen levels would rise enough to keep me going."
Prof Stewart said he was keeping the results of the experiment secret until the programme airs early next year. However, he revealed that he did suffer from severe headaches and tiredness during the challenge.
"The oxygen obviously went up enough and I got through it but not without some cost," he said. "When you go into low oxygen you are essentially going to an altitude of 4,500 metres, so there was blinding headaches and a lot of tiredness but apart from that it has worked out pretty well."
The chamber measured 2m by 8m by 2.5 metres and Prof Stewart relied upon just 120 small plants and 30 large ones to produce the vital oxygen he needed to keep him alive.