About 40 light bulbs have been taken down in hospital corridors to help an NHS trust save money.
The trust's next electric bill will show how much the move has saved
Epsom and St Helier NHS, which needs to save £24m over 18 months, said it would only know how much cash it would save when it got its next electric bill.
It said some bulbs had been removed from corridors and communal areas and no clinical areas were affected. The trust's annual electric bill is £3m.
Tom Brake MP said the "crazy" move would be funny were it not so serious.
He said: "If our hospitals are scrimping money on light bulbs, how can they afford the latest drugs and high quality patient care?"
The Liberal Democrat MP for Carshalton and Wallington said: "Patients will be left scratching their heads in the dark about this bonkers idea."
A trust statement said: "We can confirm maintenance staff have removed some light bulbs from the main corridors and some communal areas in the trust, as part of our financial recovery plan."
Energy efficiency bid
It said it was "imperative" for the trust to cut its electric bill after "significant price hikes" in the past year.
It added that it had been given funding by the strategic health authority to explore lighting and heating controls, so energy efficiency could be improved.
The trust is also bidding for further funds to explore energy efficiency measures.
The trust run two hospitals, Epsom General Hospital in Epsom, and St Helier Hospital in Carshalton, south London. It provides community services across south west London and Surrey.