But in the history of television, the gravest and most all-encompassing danger from the proximity of human bodies to a screen came in the 1950s and ’60s. In retrospect, that period might also serve as the explanation for why those of us of a certain age can recall the urgency with which our parents forbade us from sitting too close to the TV. Color sets, the new technology of the time, were found to be radioactive.

Since the 1940s, there had been long-standing concerns about radiation leaks from black-and-white picture tubes. But it wasn’t until 1967, when routine testing revealed that specific large-screen models of GE color sets were emitting “X-radiation in excess of desirable levels,” that there seemed to be any real evidence of such a risk. Scientists speculated that the high voltage required by color sets was partly to blame.

3-D TV is dead.

Initially, the radiation concern was limited to a single model, but by late in the year it became clear that televisions from almost every manufacturer were potentially affected—as many as 112,000 sets.

The response to the concern was swift. By late July of 1967, television-industry representatives were brought before a congressional committee, which eventually proposed a federal radiation-regulation bill (which became the 1968 Radiation Control for Health and Safety Act). Further testing was conducted by the National Center for Radiological Health (NCRH) and the Public Health Service into early 1968. The surgeon general eventually issued a statement, saying that testing showed that this low level of radiation posed only a small risk to any one set-owner’s health as long as he or she was watching a set in “normal viewing” conditions. That was understood to be maintaining “at least a six-foot viewing distance from the front of the screen and [avoiding] prolonged exposure at the sides, rear, or underneath a set.”

According to the NCRH, the leakage beam in most of the problematic sets was directed downward “in a thin crescent pattern.” It therefore didn’t pose a direct line of contact with a viewer’s body as long as the set was placed on the floor instead of on a high shelf. Color-set owners were also instructed to keep their distance from the set at all times and were warned against tinkering with its internals to avoid being in direct contact with the radiation beam.

The public was well aware of the potentially devastating health effects of intense radiation exposure from atomic bombs or nuclear catastrophes. But the slower impacts of lower levels of radiation were less well known. Much of the discussion in the press and in congressional hearings addressed what could happen from exposure to low-level radiation leaks over time, like the ones from color televisions. Concerns about damage to reproductive organs and about the genetic mutation of future generations were particularly common.