the following posts are from a long thread:
https://forums.macrumors.com/threads/340770/
I Make Movies (page 5, #108)
The gloss...the love it or hate thing that EVERYONE keeps bitching about. Here's what I think on the subject. Just so you know, I'm a cinematography student who knows a good amount about light, reflection, and contrast applied practically and logically. Also, this is my first post ever and I am NOT an expert on monitors.
1.) The not having an option for matte is tricky. While Apple's laptop line has the option, I am certain that the glossy screen in the laptop was not glass because adding glass would increase the weight by about 2 pounds. And, since none of us work in the plant where these iMacs are manufactured nor none of us designed them, I think that just adding a matte option is not as easy as it sounds. If it were, there'd be an option to get one. Think about trying to replace a 24" piece of flat, clean glass that's somewhere in the neighborhood of 3/16" to 1/4" in thickness with a 24" piece of matte plastic with the same thickness. I think which leads me to my next topic.
2.) Addressing the glass dealing with the reflection and contrast. The beauty of glass is it's clean and doesn't distort light, thereby making a monitor have a higher contrast ratio, which every creative person must appreciate. Why? Because the higher the contrast ratio, the greater dynamic range the monitor has. What does this have to do with reflections? Generally speaking, reflections happen because there is stronger light source behind you than what's in front of you, in this case a highly reflective piece of clean glass. A matte screen will reduce, if not almost take away, the reflection, but at a cost of the contrast ratio in 2 places. First, the matte screen itself lowers the contrast ratio, due to the nature of the plastic and it's mild light absorbing properties. Secondly, the light ambiance of the room in question will lower the contrast ratio by outside light hitting the plastic and lighting it up. You have light going both directions, out from the monitor to your eye, and in from outside light.
The amount it lowers is up to debate and/or it varies by each room and it's brightness (
http://en.wikipedia.org/wiki/Contrast_ratio), but if the outside light is bright enough, your contrast ratio will be crap on a matte screen.
Technogeek (page 6, #137)
A matte surface prevents reflections by having an irregular surface that reflects light in all directions, so that the reflected light is spread over several inches of screen. That hurts the depth of black on the screen, but gets rid of reflected images. But the irregular surface also blurs the transmission of light that goes through it, so in order for the the light emitting pixels not to get blurred together, they have to be very close to the matte surface. If you add another layer, you can't make the top layer matte, or it will blur the pixels. So the top layer has to be glossy.
Reflection could be greatly reduced by using optical coating on the top layer, which the old anti-glare screens did. Those are nano-scale coatings, and so oil from fingerprints shows up on the screen, making them get dirty looking easily. Which is why Apple probably didn't go that route.
