Recommended viewing distance for CRT TVs?

[maxhifi]

I'm curious if anyone has any materials from the CRT era which describe recommendations for optimal viewing distance for various TV sizes.

[old_tv_nut]

NTSC picture quality is optimum at a distance of about 5 picture heights. However, in most home living rooms, TV was (is?) viewed at about 10 feet distance regardless of picture size.

[maxhifi]

Originally Posted by old_tv_nut

NTSC picture quality is optimum at a distance of about 5 picture heights. However, in most home living rooms, TV was (is?) viewed at about 10 feet distance regardless of picture size.

So then say for a 13" picture tube, this should be 52 inches. I've also read that for best protection from x rays, we should be sitting at least 6 feet away from a color TV? I wonder if this 6 foot figure applies to small screen TVs, or perhaps is overly conservative.

[old_tv_nut]

The amount of X-rays generated by an electron beam is highly dependent on the value of the high voltage. The X-ray scare and the 6-foot suggestion came about with color sets that used defective high voltage regulator tubes with inadequate shielding for those tubes. The defective tubes had the internal shielding elements crooked, allowing X rays to escape. Even then, the concern was for long term effects, not immediate danger, and the industry had a mass campaign to replace defective tubes. The picture tubes themselves have always included lead in the glass to shield against X-rays (or external shielding glass in earlier sets). You may find early sets with warnings to the technician about being exposed to the back of a CRT with an open cabinet.

[maxhifi]

I think I remember reading about that. So in this case, a 1980s solid state set with a potted flyback, is more likely to be just fine at only a few feet? I've noticed though the 80s sets don't have metal shields around the back of the CRT like some older tube sets do. Would be interesting to actually measure.

[Alex KL-1]

Yes, is to be safe for our hobby uses. Of course, for watching, is a relation of it's 480i intrinsic resolution plus the resolving details of the TV circuits and CRT.