I see. So the locking in the studio was so the cameras didn't show flicker on
lighting? Or couldn't they just use DC lighting?

You're following a red herring with that line of thought. The reason
for locking to a wandering 50 or 60 Hz grid supply reference was to
stop the hum bars moving which rendered them invisible unless you
watched the TV screen at the end of the program day to detect the
vertical change of shading in the mid grey tone of the raster scan.

If the TV broadcasters hadn't locked the camera scan rates to the
mains frequency, the resulting moving hum bars would have detracted
noticably from the picture content.

By the time colour transmissions were introduced the LOPT supply
smoothing had significantly improved so that the moving hum bars could
only be observed at the end of the programming day, the change in
level due to less than perfect smoothing being too slight to be
observable during reception of program content.

LOPT supply smoothing?. What do you mean by that Johny?...


Colour broadcasting required the line and vertical scan frequencies
to be precisely locked to the colour burst reference so could no
longer take advantage of the masking effect of 'locked hum bars'.

The TV set manufacturers were effectively forced to upgrade the
smoothing performance in the power supplies as a direct result (it was
not merely coincidence that the supplies were much better smoothed
with colour TV sets).

--
Tony Sayer