Talk:Gain (projection screens)

some examples should be provided for gains != 1.0 and what they mean, e.g. gain of 1.1, gain of 1.8, gain of 2.0 -- how do they compare?

Screen gain: fundamental mistakes here?
I'm not an engineer, so I hesitate to grab the reins. But I think there is a real problem with the definition of screen gain as given.

"A gain of 1.0 means the amount of light that is projected on the screen returns to the viewer at the same brightness: none is absorbed and all is re-radiated with perfect uniformity from all viewing angles."

How does that make sense for a reflective medium? I do not believe there is any such perfectly efficient reflector in this world. Besides, screens with a gain factor greater than 1.0 would then be *adding* brightness to the image projected upon them; i.e., they would no longer be passive reflectors, they'd be adding light energy to the image somehow.

In addition, that "perfect uniformity from all viewing angles" would apply to an ideal point-source radiator, but I cannot tell what it has to do with a reflective surface. The fact is that no screen with 1.0 gain is equally bright from all viewing angles. That's why projection screens are also rated in terms of their half-angle. Half-angle in degrees defines the spread of a notional cone within which the viewer is receiving at least half the brightness obtained by viewing the screen head-on at the same distance.

There's a respectable discussion at the Screen Innovations FAQ page: 

Unless someone convinces me I am confused, I suppose I'll do the research and make the changes in line with the above. It's a pretty total re-write, though.

Infoslam (talk) 06:52, 17 September 2013 (UTC)
 * Total rewrite accomplished. The text was, in fact, wrong. The "gain" in question here is not true gain in the engineering sense (wherein a signal is actually increased in voltage, power, or some other measurement). In this case, it would be more proper to call this number a "figure of merit" as it measures the reflectivity of a given screen compared to a standard matte surface (of magnesium carbonate). No screen actually increases the amount of light scattered; some screens just reduce the amount of light scattered less than others. WikiDan61 ChatMe!ReadMe!! 20:11, 9 December 2014 (UTC)