Samsung SUHDTV Quantum Dot Display television screens are shown onstage at a press conference on CES Press Day, January 5, 2016 in Las Vegas, Nevada at the CES 2016 Consumer Electronics Show. (DAVID MCNEW/AFP/Getty Images)

SAN FRANCISCO (CBS / AP) — An environmental group on Wednesday accused three major TV manufacturers of misleading consumers and regulators about how much energy high-definition screens devour, alleging that the televisions were designed to perform more efficiently during government testing than in ordinary use.

The report by the Natural Resources Defense Council said the TVs made by Samsung, LG Electronics and Vizio saddle households with an extra $120 million in electricity bills each year and generate tons of additional pollution.

None of the manufacturers immediately responded to requests for comment. The NRDC said the companies did not dispute the findings when confronted with them.

“It appears that some major manufacturers have modified their TV designs to get strong energy-use marks during government testing but may not perform as well in consumer homes,” said Noah Horowitz, senior scientist and director for the NRDC’s center for energy efficiency standards.

The findings are based on an analysis of high-definition TVs with screens spanning at least 55 inches made in 2015 and 2016. The estimates on electricity costs are based on high-definition TVs with screens 32 inches and larger.

The study concluded that Samsung and LG have gamed the system during government testing in an effort to get better scores on the “Energy Star” yellow labels that appear on the sets in stores. Those scores often influence the buying decisions of consumers looking to save money on their utility bills.

The report said Samsung and LG did not break any laws in their manipulation of the tests, but rather exploited weaknesses in the Department of Energy’s system to measure electricity usage. The Samsung and LG sets have a dimming feature that turns off the screens’ backlight during part of the 10-minute video clip used in government tests. But that does not typically happen when the sets are being used in homes to watch sports, comedies, dramas and news programming.

The analysis also found that Samsung, LG and Vizio disable energy-saving features in their TVs when consumers change the factory setting on the picture, a common practice. The energy-saving feature is turned off, with little or no warning on the screen, sometimes doubling the amount of electricity consumed, according to the NRDC report.

Add it all up, and the report estimates that the collective electricity bills during a decade of watching the high-definition TVs will be $1.2 billion higher than the energy ratings imply. The higher energy usage generates an additional 5 million metric tons of carbon pollution, potentially affecting the climate, the report warned.

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