Independent lab tests have found that some Samsung TVs in Europe appear to use less energy during official testing conditions than they do during real-world use, raising questions about whether they are set up to game energy efficiency tests.

The European commission says it will investigate any allegations of cheating the tests and has pledged to tighten energy efficiency regulations to outlaw the use of so-called “defeat devices” in TVs or other consumer products, after several EU states raised similar concerns.

The apparent discrepancy between real-world and test performance of the TVs is reminiscent of the VW scandal that originated in the US last week. The car company has admitted fitting software to 11m diesel vehicles worldwide which meant the cars produced less pollution during testing than real-world driving.

Samsung strongly denies that its TVs’ “motion lighting” feature is designed to fool official energy efficiency tests or that it constitutes a defeat device. The company says it reduces screen brightness in response to numerous types of real-world content including fast-moving action movies and sports and slower moving footage such as weather reports - not just during test conditions.

“There is no comparison [between motion lighting and VW defeat devices],” a Samsung spokesman said. “This is not a setting that only activates during compliance testing. On the contrary, it is an ‘out of the box’ setting, which reduces power whenever video motion is detected. Not only that, the content used for testing energy consumption has been designed by the international electrotechnical commission to best model actual average picture level internationally.”

The apparent differences came to light in unpublished lab tests by an EU-funded research group called ComplianTV which recorded consistently higher energy consumption rates for the company’s models in real-world situations than in official test conditions.

The lab studies found that Samsung’s ‘motion lighting’ feature reduced the TV sets’ brightness – and power consumption – under international electrotechnical commission (IEC) test conditions. These involve the playback of fast sequences of varied material, such as recorded TV shows, DVDs and live broadcasts.

But under real-world viewing conditions, no reductions in power consumption were registered, making the sets’ power consumption, fuel bills and carbon emissions correspondingly higher.

After tests in February, a ComplianTV report, which did not name Samsung, said: “The laboratories observed different TV behaviours during the measurements and this raised the possibility of the TV’s detecting a test procedure and adapting their power consumption accordingly. Such phenomenon was not proven within the ComplianTV tests, but some tested TVs gave the impression that they detected a test situation.”

“Samsung is meeting the letter of the law but not the spirit of the law,” Rudolf Heinz, the project manager of ComplianTV’s product lab, told the Guardian.

Some of the ComplianTV study results were presented at a Royal Society meeting sponsored by the Energy Saving Trust in London on Tuesday.

There is no suggestion that Samsung, the world’s biggest TV manufacturer, behaved illegally, although energy efficiency campaigners claim that EU testing procedures are overly generous.

In response to a Guardian inquiry, the European commission pledged to outlaw the use of defeat devices within the bloc’s TV ecodesign regulations, and said that any allegations of their use would be fully investigated.

“The commission is proposing specific text to clarify that [the use of defeat devices] is illegal and that products found to behave differently under test conditions cannot be considered compliant,” a spokesperson said. “The commission will investigate whether this practice is used in other product sectors.”

Several EU states have already complained about the problem, including the Swedish Energy Agency in a letter to the European commission earlier this year.

“The Swedish Energy Agency’s Testlab has come across televisions that clearly recognise the standard film (IEC) used for testing,” says the letter, which the Guardian has seen. “These displays immediately lower their energy use by adjusting the brightness of the display when the standard film is being run. This is a way of avoiding the market surveillance authorities and should be addressed by the commission.” The letter did not name any manufacturers.

“There’s more than a whiff of diesel fumes coming out of this, with officials finding gadgets that recognise test conditions and alter their behaviour,” said Jack Hunter, a spokesman for the European Environmental Bureau an environmental watchdog funded by European governments and international bodies. “If deception is proved for TVs, there’s bound to be a fresh hoard of angry customers à la Volkswagen.”

Three years earlier, the UK also told the commission that it had received intelligence indicating that some TVs had been pre-installed with default software settings that changed static video signals to dynamic ones, reducing luminance and power consumption.

“The purpose seems to be to pass the peak luminance measurement test and then reduce luminance (and power) to get a better energy label ranking when the on power is measured,” the correspondence says. “All very clever and it is not dimming so much that it makes a huge difference, but does the commission consider this an acceptable practice or is this a non-compliant activity?”

The commission did not respond to a request for its answer to the question. But one UK market surveillance officer told the Guardian that the use of defeat devices was “an area of increasing risk to us – not just in TVs but across the board and future programmes are being duly adjusted to look at these areas.”

Research underway by the National Resources Defense Council (NRDC) in the US has also uncovered what Noah Horowitz, the NRDC’s director for energy efficiency standards called “a curious anomaly with one manufacturer’s TV’s”.

More testing is planned to establish whether manufacturers are gaming television testing procedures. But “it wouldn’t take much for an unscrupulous manufacturer to install software to detect the unique ‘signature’ of the test and to then have the unit go into some sort of eco-mode and produce superior results (ie lower energy use) that wouldn’t occur under normal usage,” Horowitz said.

Televisions typically consume up to 10% of a typical household’s electricity use, according to coolproducts, a coalition of NGOs which campaigns for energy-saving product designs. The group says that across Europe, TVs now account for as much energy use as the combined electricity consumption of Sweden and Portugal, and that this figure is growing.

