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Controlling light reflection.
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WanMan



Joined: 19 Mar 2006
Posts: 10261



PostLink    Posted: Mon Aug 25, 2008 10:41 am    Post subject: Controlling light reflection. Reply with quote


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Controlling light reflection in your theater room. How do you control, if at all, the light reflected off of the screen and onto the wall, floor, and ceiling surfaces. This is waste light that acts to elevate the ambient light level, and as a result hinders the quest for low black levels.

So, how are you controlling this little devil?

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garyfritz



Joined: 08 Apr 2006
Posts: 10576
Location: Fort Collins, CO


PostLink    Posted: Mon Aug 25, 2008 2:28 pm    Post subject: Reply with quote

I have dark-colored walls, and large black-covered sound-absorption panels on either side of the screen. They come out at a 45deg angle so they capture some light.

If you want to get hardcore about it, you hang black velvet on the walls AND the ceiling for at least 6' or so from the screen.

EDIT: pic!



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Last edited by garyfritz on Mon Aug 25, 2008 4:10 pm; edited 1 time in total
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JustGreg



Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI


PostLink    Posted: Mon Aug 25, 2008 3:29 pm    Post subject: Reply with quote

I have pretty much the same configuration as Gary. The room is split in half by a boxed in beam. The ceiling from screen to beam is black muslin king sized sheets. The screen sits under boxed in ductwork. The duct box and walls to each side of the screen are flat black.

The rest of the walls are painted a custom color that's a little darker than a regal maroon/red matte finish. I have curtains ~3ft out from the screen to each side and over the center part of the screen (attached to the boxed in ducting) is a scalloped valance of the same color as the curtains.

The carpeting is 2ftx2ft squares. Not sure how to decribe the color other than gray blue with circular patterns.

I've got to redo the rear wall for a couple reasons. One is light bounce. The other is... I bought this CHEAP A$$ED paneling that's a light pine 'finish', but wood it ain't. I had masked off the edges of it while painting the walls and when I removed the tape, I removed the wood grain. Nuttin underneath but cardboard. Evil or Very Mad So that has to be drywalled and painted the same color as the rest. Then I'll take a shot at building some traps.



BTW, the string hanging from the light (I've since remove those sconce lights. They accomplished nothing) is actually connected to the center line of the screen (stapled to the frame). There's another one attached to the top, dead center. When I do a 'from scratch' setup or to check things, I pull it across and attach it to the wood frame center mark and the same from the top and `voila...instant bullseye.
(Pay no attention to the crap behind that curtain. That's my butt kickers and 'things-yet-to-be-done' pile)

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Greg

"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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JustGreg



Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI


PostLink    Posted: Mon Aug 25, 2008 4:35 pm    Post subject: Reply with quote

garyfritz wrote:
I have dark-colored walls, and large black-covered sound-absorption panels on either side of the screen. They come out at a 45deg angle so they capture some light.

If you want to get hardcore about it, you hang black velvet on the walls AND the ceiling for at least 6' or so from the screen.

EDIT: pic!

VERY nice!!!!! Excellent job. Thumbs Up

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Greg

"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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ecrabb
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Joined: 13 Mar 2006
Posts: 15909
Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Mon Aug 25, 2008 4:39 pm    Post subject: Reply with quote

Medium walls, darker ceiling, mostly black carpet, dark acoustic panels at first reflections... All that stuff soaks up light. I probably get more reflection from somebody wearing a white tee shirt in the front row than from anything in the room.





I still need to trim the room out. I need to stop watching movies and get some work done!!!

SC
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kal
Forum Administrator


Joined: 06 Mar 2006
Posts: 15675
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Tue Aug 26, 2008 2:08 am    Post subject: Reply with quote

garyfritz wrote:
If you want to get hardcore about it, you hang black velvet on the walls AND the ceiling for at least 6' or so from the screen.

That's what I do. entire screen wall is black (it's the least important actually for light bounce) as well as the first 6 feet of ceiling and side wall(s).

Walls are chocolate brown flat texture to help too, though they could be darker still.

Kal

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Gino



Joined: 22 Apr 2006
Posts: 1363
Location: Trinity Beach, AUSTRALIA


PostLink    Posted: Tue Aug 26, 2008 6:28 am    Post subject: Reply with quote

I think building a screenwall with the screen sunken in (like one of my friends has in the picture) would work wonders for minimising impact of reflected light coming from other directions.


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WanMan



Joined: 19 Mar 2006
Posts: 10261



PostLink    Posted: Tue Aug 26, 2008 9:01 am    Post subject: Reply with quote

I'd be curious to see an extended exposure of the walls when something is playing on the screen (and with the lights turned out). This is often one of the more difficult things to represent in a capture, though.
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ecrabb
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Joined: 13 Mar 2006
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Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Tue Aug 26, 2008 3:01 pm    Post subject: Reply with quote

Funny - I've actually thought about doing that. Might be interesting. I'll try to give it a whirl this weekend... I'll see how closely I can match how it looks when I'm actually sitting in the room.

SC
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garyfritz



Joined: 08 Apr 2006
Posts: 10576
Location: Fort Collins, CO


PostLink    Posted: Tue Aug 26, 2008 6:48 pm    Post subject: Reply with quote

I dunno Gino, I doubt it would help all that much. It's only blocking the light that reflects at extreme angles (from screen to wall). Most of the light, even for a 1.0-gain screen, is going to be reflecting at angles that will bypass the setback. If your screen gain is higher than 1.0, then almost ALL of the light will reflect at too step an angle to hit the setbacks. All that light can then hit the walls and carpet and bounce back at the screen.

If that setback gets you X improvement, I'd bet your friend would get at least 5X improvement by painting his walls the same color as his ceiling. Even more with dark carpet.
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dropzone7



Joined: 12 Jun 2007
Posts: 1069
Location: Charlotte, NC


PostLink    Posted: Tue Aug 26, 2008 7:15 pm    Post subject: Reply with quote

I went for the cave effect except for my ceiling which is in terrible need of some black fabric or velvet or something. I probably have enough of the fabric I used on the walls left to cover a few feet out from the screen on the ceiling. I can't decide if I want to do that or make black fabric covered panels to attach to the ceiling. If I did it would only be at the front 1/3rd of the ceiling.


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ecrabb
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Joined: 13 Mar 2006
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Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Tue Aug 26, 2008 7:42 pm    Post subject: Reply with quote

garyfritz wrote:
I dunno Gino, I doubt it would help all that much. It's only blocking the light that reflects at extreme angles (from screen to wall). Most of the light, even for a 1.0-gain screen, is going to be reflecting at angles that will bypass the setback. If your screen gain is higher than 1.0, then almost ALL of the light will reflect at too step an angle to hit the setbacks. All that light can then hit the walls and carpet and bounce back at the screen.


I disagree, Gary. Don't forget about the the law of inverse squares. You're right that a lot of the light will miss the shadow the box and fall on the ceiling. But, if the light travels twice as far as without the shadow box before being reflected (say 2 feet instead of 1 foot), the amount of light that can be reflected back to the screen will only be 1/4 of what it was.

Short of painting the room flat black, using black shag carpet with black fabric chairs, and wearing black clothes with black face paint, everything else will be some degree of compromise. A black shadow box in concert with darker wall/ceiling colors will go a LONG way to reducing reflected light to very low levels.

SC
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CRT_Ben



Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia


PostLink    Posted: Tue Aug 26, 2008 7:52 pm    Post subject: Reply with quote

ecrabb wrote:
garyfritz wrote:
I dunno Gino, I doubt it would help all that much. It's only blocking the light that reflects at extreme angles (from screen to wall). Most of the light, even for a 1.0-gain screen, is going to be reflecting at angles that will bypass the setback. If your screen gain is higher than 1.0, then almost ALL of the light will reflect at too step an angle to hit the setbacks. All that light can then hit the walls and carpet and bounce back at the screen.


I disagree, Gary. Don't forget about the the law of inverse squares. You're right that a lot of the light will miss the shadow the box and fall on the ceiling. But, if the light travels twice as far as without the shadow box before being reflected (say 2 feet instead of 1 foot), the amount of light that can be reflected back to the screen will only be 1/4 of what it was.

Short of painting the room flat black, using black shag carpet with black fabric chairs, and wearing black clothes with black face paint, everything else will be some degree of compromise. A black shadow box in concert with darker wall/ceiling colors will go a LONG way to reducing reflected light to very low levels.

SC


Ok, I think I see what you're saying. That the shadow box is eliminating the light that would hit the floor/walls/ceiling closest to the screen, and narrowing the "cone" of light that bounces from the screen, thus the light within the cone must hit any room elements further away from the screen than without the shadow box. The extreme of this situation is viewing a screen at the end of a very long, velvet tunnel. Obviously very little light would be returned to the screen in that situation. Am I making any sense??
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ecrabb
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PostLink    Posted: Tue Aug 26, 2008 8:16 pm    Post subject: Reply with quote

Exactly. What light does come back is much less intense than the light that could come from immediately adjacent walls, floor and ceiling. Also, don't forget that that most of the surfaces the light from the screen does hit are lambertian reflectors (diffuse) and won't reflect all the light back directly at the screen and instead scatter the light.

SC
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garyfritz



Joined: 08 Apr 2006
Posts: 10576
Location: Fort Collins, CO


PostLink    Posted: Tue Aug 26, 2008 8:52 pm    Post subject: Reply with quote

Inverse-square law works for a point light source. For a planar light source, there is very little dropoff with distance -- none, for an ideal infinite plan. A screen is between a point and a plane, depending on how far away you are, but the bottom line is that you don't get THAT much dropoff with distance. I doubt you'd even get linear dropoff with distance, since that's what you'd get for an idealized linear light source.

Also, the light that would be blocked by the setback will have limited effect when it bounces back to the screen, since it will be arriving at such an oblique angle. Whereas light reflecting from further points on the side walls, and from floor / back wall / etc, will hit the screen fairly straight-on.

I don't doubt the setback can help, a little. But I think it will be very little compared to darkening the walls and floor.
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AFryia



Joined: 09 Mar 2006
Posts: 917
Location: S.E. Michigan VPH-G70Q


PostLink    Posted: Wed Aug 27, 2008 1:43 am    Post subject: Reply with quote

I just painted the front wall and sofit sides flat black. The ceiling between the PJ and front wall is also flat black.

My speakers are actual ash color, they are stretch wrapped in black speaker cloth. I greatly under estimated the light reflection.
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WanMan



Joined: 19 Mar 2006
Posts: 10261



PostLink    Posted: Wed Aug 27, 2008 8:52 am    Post subject: Reply with quote

ecrabb wrote:
garyfritz wrote:
I dunno Gino, I doubt it would help all that much. It's only blocking the light that reflects at extreme angles (from screen to wall). Most of the light, even for a 1.0-gain screen, is going to be reflecting at angles that will bypass the setback. If your screen gain is higher than 1.0, then almost ALL of the light will reflect at too step an angle to hit the setbacks. All that light can then hit the walls and carpet and bounce back at the screen.


I disagree, Gary. Don't forget about the the law of inverse squares. You're right that a lot of the light will miss the shadow the box and fall on the ceiling. But, if the light travels twice as far as without the shadow box before being reflected (say 2 feet instead of 1 foot), the amount of light that can be reflected back to the screen will only be 1/4 of what it was.

Short of painting the room flat black, using black shag carpet with black fabric chairs, and wearing black clothes with black face paint, everything else will be some degree of compromise. A black shadow box in concert with darker wall/ceiling colors will go a LONG way to reducing reflected light to very low levels.

SC

But its not the light falling back onto the screen that one needs to address. Light coming off the screen and bouncing off the walls and into your eyes will assist create a higher level of blackness. No different than if someone had soft floor lighting point up at my eyes, on wall sconces left on.

So, while reflected light may make it back onto the screen, its not the only concern of waste light about the room. And I am think of painting the room flat black, and using crushed velvet on the forward third of the room's surfaces. Of course, I am all about the picture and nothing about the ornateness.

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garyfritz



Joined: 08 Apr 2006
Posts: 10576
Location: Fort Collins, CO


PostLink    Posted: Wed Aug 27, 2008 3:04 pm    Post subject: Reply with quote

WanMan wrote:
But its not the light falling back onto the screen that one needs to address.

!? Yes it is! Light reflecting off white walls bounces back onto the screen. This raises the noise floor and wrecks your ANSI contrast. It won't affect the fade-to-black performance but it will cause light spill from bright areas into dark areas. I'd go so far as to say there's no point in moving to an LC projector if you have light walls. LC will help, but painting the walls is cheaper and will probably have more effect.
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WanMan



Joined: 19 Mar 2006
Posts: 10261



PostLink    Posted: Thu Aug 28, 2008 8:57 am    Post subject: Reply with quote

Gary, I am saying its not ONLY re-reflected light from the screen. Its light reflected off the screen for a second time, AND light reflected off the walls and into my eyes. So, not saying you or anyone else was wrong, but just not the only source of light entering the eyeballs.

You eyeballing me, son?

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garyfritz



Joined: 08 Apr 2006
Posts: 10576
Location: Fort Collins, CO


PostLink    Posted: Thu Aug 28, 2008 3:29 pm    Post subject: Reply with quote

Yer not my type. Smile

OK, so you're talking about light that hits the screen, bounces off and hits light-colored objects in the room, and then goes either direct to your eye or hits the screen and goes to your eye, right?

I say neither of those "create a higher level of blackness," or at least not a desirable one. By definition this can only happen when there are bright areas on the screen, yes? We're not talking about fade-to-black blacks. We're only taking about shadow detail when there are bright areas on the screen -- ANSI contrast. And both of those reflections-off-light-objects will reduce your ANSI contrast.

Bouncing off the screen reduces it directly, by increasing the noise level on the screen. Bouncing directly into your eye will IMHO have very little effect, but what effect it has will be to constrict your pupil and otherwise overwhelm the very dark areas of the screen.

All of those effects are undesirable.
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