On Sun, 14 Jan 2018 19:46:54 GMT, DerbyBorn wrote:

How do TV productions get such visible beams of light from some of their
effects lights?

By having diffused "smoke" in the air. There are various machines to
do this, for the effect you are describing you'd use a "hazer" this
just emits a gentle but steady stream of "smoke". Hidden round the
back of the set somewhere it'll build up a haze in a fairly large
enclosed space in about 1/2 an hour.

"smoke" this used to be vaporised mineral oil, ie squirt oil onto
something hot and blow the result out of the box. I think they now
use compressed air to atomise the oil. And there are water based
options.

--
Cheers
Dave.