The finding, published this week in the British Medical Journal, proves what experts long suspected.
Previous research has found smokers of "lighter" cigarettes compensate by taking deeper drags, holding the smoke longer and smoking more cigarettes. Scientists suspected they would probably be just as vulnerable to lung cancer and other diseases as those who smoke harsher varieties.
"It's not surprising, but it's very important," said Stan Glantz, a professor of cardiology at the University of California, San Francisco, who was not involved with the research. "It's always important to demonstrate whether a theoretical prediction is right or wrong."
Tobacco industry representatives said manufacturers never claimed light or mild cigarettes were safer, and don't dispute the study's findings.
The study, conducted by scientists at Massachusetts Institute of Technology and the American Cancer Society, examined the link between the tar rating of the cigarette smoked in 1982 and deaths from lung cancer in the subsequent six years among 940,774 Americans over the age of 30 who were smokers, former smokers or had never smoked.
Those who smoked strong non-filtered cigarettes had a higher risk of lung cancer than those who smoked conventional filtered cigarettes.
However, the study found no difference in the lung cancer death rate among those who smoked the medium filtered cigarettes and those who used mild or ultra light varieties.
The results held true after other factors known to influence lung cancer, such as age, education level, intake of fruits and vegetables, and duration of smoking, had been taken into account.
The findings were the same for men and women.
"There was not a shred of evidence of reduced risk," said investigator Michael Thun, epidemiology chief at the American Cancer Society. "The ultra light haven't been used as long as the light and it is possible that some difference in risk might emerge with longer term use of the ultra light, but this is very, very solid for the low tar."
Thun and Glantz said the findings will bolster the lawsuits of U.S. plaintiffs who are suing tobacco companies on the grounds of consumer fraud. The cases allege that smokers were duped into believing that low-tar cigarettes were less hazardous.
Lower-tar cigarette varieties were developed in the late 1960s and early 1970s.
Tim Lord, chief executive of the London-based Tobacco Manufacturers Association, said this was in response to government calls, because government scientists believed that they might reduce the risks.
In the United States, industry was similarly encouraged by health authorities to develop cigarettes yielding less tar, in the hope that such a move would reduce the risks, said Steve Kottak, spokesman for Kentucky-based cigarette maker Brown & Williamson.
Tar levels were classified by using a smoking machine. The low tar cigarettes, with more porous paper and ventilation holes around the filter, scored lower on the machine.
However, scientists later discovered the machine did not accurately reflect what happens when people smoke. Smokers of light cigarettes tended to cover up the perforations, draw harder on the cigarettes and compensate in other ways that meant they got the same kick as from regular cigarettes.
"This was not a dastardly plot by the tobacco industry to launch products on health claims," Lord said. "We never claimed it to be safer and we did it at the request of the government. We were even asked to spend more of our advertising and promotional pounds to promote the lighter products than the stronger products."
In 2001 the European Union banned the use of language such as "mild," "light" and "low tar" on cigarette packs, and a global anti-smoking treaty passed last year by the World Health Organization also limits the use of such terms.
By Emma Ross