Bias lighting for front projection setup? - AVS Forum
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post #1 of 25 Old 05-09-2012, 10:34 AM - Thread Starter
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Would there be any benefit using bias lighting (like the ideal lume) for a front projection setup? I currently have a dropdown 92" screen that rolls down in front of my 55" plasma. I was considering getting some bias lighting and mounting it behind my plasma, but I've noticed I really haven't been using the 55" anymore for movies. But if bias lighting will help on a front projector setup, then I may just spring for it and hope the light will reach far out enough behind the screen. I have an Optoma GT750 projector, which is one of the brighter projectors on the market.
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post #2 of 25 Old 05-09-2012, 10:44 AM
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Originally Posted by gundam83 View Post

Would there be any benefit using bias lighting (like the ideal lume) for a front projection setup?

No ... it would just make things worse.

The main reason for bias lighting is to stimulate (and "bias") your entire field of vision. This is not necessary with front projection ...

OTOH, it would probably help with your plasma.
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post #3 of 25 Old 05-09-2012, 10:44 AM
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Quote:
Originally Posted by gundam83 View Post

Would there be any benefit using bias lighting (like the ideal lume) for a front projection setup? I currently have a dropdown 92" screen that rolls down in front of my 55" plasma. I was considering getting some bias lighting and mounting it behind my plasma, but I've noticed I really haven't been using the 55" anymore for movies. But if bias lighting will help on a front projector setup, then I may just spring for it and hope the light will reach far out enough behind the screen. I have an Optoma GT750 projector, which is one of the brighter projectors on the market.

I don't think bias lighting is meant for FP's. It would be ideal for a Plasma, though.
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post #4 of 25 Old 05-09-2012, 10:45 AM
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Jinx!!!
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post #5 of 25 Old 05-09-2012, 10:48 AM - Thread Starter
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Great! I may still get one for my bedroom plasma as I use that more often than the plasma in my living room. Plus it's one of the infamous Panny sets from the "rising black levels" fiasco a few years back. Hopefully the bias lighting will help trick my eyes into seeing darker blacks.
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post #6 of 25 Old 05-09-2012, 11:19 AM
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Quote:
Originally Posted by gundam83 View Post

Would there be any benefit using bias lighting (like the ideal lume) for a front projection setup? I currently have a dropdown 92" screen that rolls down in front of my 55" plasma. I was considering getting some bias lighting and mounting it behind my plasma, but I've noticed I really haven't been using the 55" anymore for movies. But if bias lighting will help on a front projector setup, then I may just spring for it and hope the light will reach far out enough behind the screen. I have an Optoma GT750 projector, which is one of the brighter projectors on the market.

I always use bias lighting with my tiny front projection setup. My small Dalite HP 2.8 is as bright as a plasma, so in complete darkness it is to bright. I have the screen out in an entrance archway (acts like a shadow box) By placing bias lighting in the corners of the room on either side of the arch, the light does not fall on the screen that is outside the room. It is just enough light to eliminate the eye strain, but not enough to see the remote.. I don't have the fancy proper color light, but am happy non the less with the results. I am not sure how well it would work behind the screen, you would have to make sure that it does not light up the screen or you will really hurt the blacks. Of course the bias light will keep you pupil closed and the blacks will hopefully look blacker than if you were in total darkness.
Yes it works with over bright front projection as long as you keep the light low and off the screen.
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post #7 of 25 Old 05-09-2012, 11:40 AM
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Quote:
Originally Posted by gundam83 View Post

Would there be any benefit using bias lighting (like the ideal lume) for a front projection setup? I currently have a dropdown 92" screen that rolls down in front of my 55" plasma. I was considering getting some bias lighting and mounting it behind my plasma, but I've noticed I really haven't been using the 55" anymore for movies. But if bias lighting will help on a front projector setup, then I may just spring for it and hope the light will reach far out enough behind the screen. I have an Optoma GT750 projector, which is one of the brighter projectors on the market.

The greatest fundamental issue that necessitates bias lighting is excessive screen brightness while viewing in a dark-adapted state. The key to understanding proper video display system design starts with a solid understanding of the human visual system and its limitations. Front projection display systems use typical recommended screen brightness levels far lower than direct-view type displays, even though both display types perform their best in a darkened viewing environment (12 to 18 fL versus 30 to 35 fL). Front projection benefits from total darkness, but TVs are engineered to compete with ambient light in residential viewing environments for mass market appeal. The most critical component in every video display system will always be the viewer.

Best regards and beautiful pictures,
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A Lion AV Consultants affiliate

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post #8 of 25 Old 05-10-2012, 08:13 AM
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Originally Posted by PlasmaPZ80U View Post

I don't think bias lighting is meant for FP's, since the screen is on the wall and covers the entire FOV. It would be ideal for a Plasma, though.

There's no reason the screen has to be on a wall. It's actually BETTER for the screen NOT to be on a wall. When the screen is on legs away from a wall you can place the loudspeakers so they sound their best, then put the screen even with the front set of speakers. In my current setup, there's 9 feet of space behind the screen. Front projection optimized for image quality with a neutral (or reference quality) screen with no or modest gain work best in fully darkened rooms to prevent ANY light in the room from reaching the screen and raising black levels.

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post #9 of 25 Old 05-10-2012, 09:22 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

I don't think bias lighting is meant for FP's, since the screen is on the wall and covers the entire FOV. It would be ideal for a Plasma, though.

By the way, if the screen image fills the viewer's entire field of view (FOV), that's sitting much closer than recommended for a 1920 x 1080 resolution. A horizontal viewing angle of 30 degrees is considered maximum for 20/20 vision. The closest comparison to what you imply would be IMAX film. IMAX film resolution has been equivalently compared to 8K resolution or better. FOV is also not nearly as impacting a factor on eye strain/viewing fatigue as image brightness and vertical viewing angle.
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post #10 of 25 Old 05-10-2012, 09:34 AM
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Originally Posted by Doug Blackburn View Post

There's no reason the screen has to be on a wall. It's actually BETTER for the screen NOT to be on a wall. When the screen is on legs away from a wall you can place the loudspeakers so they sound their best, then put the screen even with the front set of speakers. In my current setup, there's 9 feet of space behind the screen. Front projection optimized for image quality with a neutral (or reference quality) screen with no or modest gain work best in fully darkened rooms to prevent ANY light in the room from reaching the screen and raising black levels.

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Originally Posted by GeorgeAB View Post

By the way, if the screen image fills the viewer's entire field of view (FOV), that's sitting much closer than recommended for a 1920 x 1080 resolution. A horizontal viewing angle of 30 degrees is considered maximum for 20/20 vision. The closest comparison to what you imply would be IMAX film. IMAX film resolution has been equivalently compared to 8K resolution or better. FOV is also not nearly as impacting a factor on eye strain/viewing fatigue as image brightness and vertical viewing angle.

fair enough, I'm not familiar with FP setups aside from the cinema so I guess I made some incorrect assumptions... I've edited my original post.

however, would either of you recommend bias lighting for a FP setup?
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post #11 of 25 Old 05-10-2012, 09:47 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

fair enough, I'm not familiar with FP setups aside from the cinema so I guess I made some incorrect assumptions... I've edited my original post.

however, would either of you recommend bias lighting for a FP setup?

Not typically required or recommended, but some unusual setups may benefit from it when conditions include elements already described in the thread.
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post #12 of 25 Old 05-10-2012, 10:15 PM
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Originally Posted by GeorgeAB View Post

Not typically required or recommended,

Like I said.

FWIW, I suspect that many if not most folks that try to cram more than a 92" screen into their home "theater" rooms are probably sitting too close for comfort ... aka the front row effect. I suspect that even 92" in my room would be right on the edge of "too much."
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post #13 of 25 Old 05-12-2012, 08:28 AM
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The size of the screen doesn't matter. It's all about viewing angle.

And there's essentially no "front row effect" in home theater because, if you've setup the screen properly, your head is probably somewhere between the center and 1/3-up-from-the-bottom of the screen. In a movie theater in the front row, your head is typically at the bottom of the screen or even below the bottom of the screen so you are always looking up from a much too low angle.

HD video has enough resolution that you cannot see individual pixels if you are below a 50-degree viewing angle. So how close are you with a 50-degree viewing angle?

With a 72" wide screen (6-foot) - just under 6.5 feet
With a 96" wide screen (8-foot) - 8.55 feet

If you were using a 60" diagonal panel, a 50 degree angle would mean sitting 4.9 feet from the screen.

I sit 7 feet from a 6-foot wide screen and there is NOTHING uncomfortable about it. In fact, it is much more like what we experience in real life... your peripheral vision is (mostly) filled with image at the edge of the screen while your attention tends to focus in the center unless something causes you to look to the sides. Movies are made to be viewed this way. But a lot of people have some kind of phobia about "sitting too close" --- there is such a thing as too close, but you know it once you get there.

A lot of people are obsessed with large screen sizes but end up sitting so far away from the screen, their viewing angle is no better than what they'd get from sitting 10 feet from a 60" diagonal panel (that would require a VERY large theater room, but it happens more often than you'd think). Viewing a 6-foot screen from 7 feet (46.4 degree viewing angle) is a more immersive and enjoyable experience than viewing a 15 foot screen from 22 feet (37. 6 degree viewing angle).

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post #14 of 25 Old 05-12-2012, 09:54 AM
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Quote:
Originally Posted by Doug Blackburn View Post

The size of the screen doesn't matter. It's all about viewing angle.

Yes ... but around these parts, most folks seem to think that anything less than 106" diagonal isn't worth the effort. ... How close are they sitting, I wonder.

FWIW, I've had a 92" 16:9 area taped off on my wall for about a year while I've been dithering on moving to FP ... I've got to say that at about 9.5-10ft from my intended viewing position, it feels right on the edge of being "too much." Especially considering the finished installation will have the screen another 4-6" closer to accommodate a flat screen mounted on the wall behind the screen.

Maybe, I'll feel different once I have an actual picture up, or maybe it'll just turn out to be a horrible mistake once I can see every little compression flaw ...

In any case, HVAC issues trump home theater at the moment.
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post #15 of 25 Old 05-12-2012, 11:49 AM
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Quote:
Originally Posted by Doug Blackburn View Post

The size of the screen doesn't matter. It's all about viewing angle.

And there's essentially no "front row effect" in home theater because, if you've setup the screen properly, your head is probably somewhere between the center and 1/3-up-from-the-bottom of the screen. In a movie theater in the front row, your head is typically at the bottom of the screen or even below the bottom of the screen so you are always looking up from a much too low angle.

HD video has enough resolution that you cannot see individual pixels if you are below a 50-degree viewing angle. So how close are you with a 50-degree viewing angle?

With a 72" wide screen (6-foot) - just under 6.5 feet
With a 96" wide screen (8-foot) - 8.55 feet

If you were using a 60" diagonal panel, a 50 degree angle would mean sitting 4.9 feet from the screen.

I sit 7 feet from a 6-foot wide screen and there is NOTHING uncomfortable about it. In fact, it is much more like what we experience in real life... your peripheral vision is (mostly) filled with image at the edge of the screen while your attention tends to focus in the center unless something causes you to look to the sides. Movies are made to be viewed this way. But a lot of people have some kind of phobia about "sitting too close" --- there is such a thing as too close, but you know it once you get there.

A lot of people are obsessed with large screen sizes but end up sitting so far away from the screen, their viewing angle is no better than what they'd get from sitting 10 feet from a 60" diagonal panel (that would require a VERY large theater room, but it happens more often than you'd think). Viewing a 6-foot screen from 7 feet (46.4 degree viewing angle) is a more immersive and enjoyable experience than viewing a 15 foot screen from 22 feet (37. 6 degree viewing angle).

Doug,

We agree on most things, but not on this one. Average human visual acuity has long been established and consistently verified in the scientific community as being one arc minute (one 60th of a degree) for average 20/20 vision. For 1920 x 1080 HDTV, this works out to a 30 degree viewing angle. Seating distance for a 30 degree angle equates to approximately 3 times the screen height, or 1.5 times the diagonal. Do you have any documentation supporting a 50 degree viewing angle for average acuity? It may look fine to you, but my personal experience has supported the 30 degree industry consensus. Granted, low contrast ratio, low image brightness, and motion can mask pixel definition in varying degrees. However, I have little problem detecting pixel structure at much closer than three screen heights (1.78:1 aspect).

http://www.poynton.com/PDFs/HDTV_Desktop_Computing.pdf
http://www.ndt-ed.org/EducationResou...sualacuity.htm
http://webvision.med.utah.edu/book/p...visual-acuity/
http://www.audioholics.com/education...f-human-vision
http://www.nhk.or.jp/digital/en/tech.../ibc200502.pdf
http://tech.ebu.ch/docs/techreview/trev_308-hdtv.pdf
http://archiv.arri.de/4kplus-systems/index.htm
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post #16 of 25 Old 05-12-2012, 12:37 PM
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Quote:
Originally Posted by HDTVChallenged View Post

Yes ... but around these parts, most folks seem to think that anything less than 106" diagonal isn't worth the effort. ... How close are they sitting, I wonder.

FWIW, I've had a 92" 16:9 area taped off on my wall for about a year while I've been dithering on moving to FP ... I've got to say that at about 9.5-10ft from my intended viewing position, it feels right on the edge of being "too much." Especially considering the finished installation will have the screen another 4-6" closer to accommodate a flat screen mounted on the wall behind the screen.

Maybe, I'll feel different once I have an actual picture up, or maybe it'll just turn out to be a horrible mistake once I can see every little compression flaw ...

In any case, HVAC issues trump home theater at the moment.

I think you might be able to get away with it if you only watch BD content like movies and TV shows. However, with regular HDTV programming I doubt you'll want to sit that close unless you want to see every flaw in the picture due to compression and upscaling (not all HD content is native HD). I think this applies to both flat-panels and FP setups. I'm more inclined to agree with George on this one.
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post #17 of 25 Old 05-12-2012, 11:17 PM
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Originally Posted by PlasmaPZ80U View Post

I think you might be able to get away with it if you only watch BD content like movies and TV shows. However, with regular HDTV programming I doubt you'll want to sit that close unless you want to see every flaw in the picture due to compression and upscaling (not all HD content is native HD). I think this applies to both flat-panels and FP setups. I'm more inclined to agree with George on this one.

Yes. There is more than one reason why I downsized from a 50" RPTV to my current 42" LG. Hiding compression artifacts ranks among the top 2 or 3.
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post #18 of 25 Old 05-13-2012, 08:10 AM
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Originally Posted by GeorgeAB View Post

Doug,

We agree on most things, but not on this one. Average human visual acuity has long been established and consistently verified in the scientific community as being one arc minute (one 60th of a degree) for average 20/20 vision. For 1920 x 1080 HDTV, this works out to a 30 degree viewing angle. Seating distance for a 30 degree angle equates to approximately 3 times the screen height, or 1.5 times the diagonal. Do you have any documentation supporting a 50 degree viewing angle for average acuity? It may look fine to you, but my personal experience has supported the 30 degree industry consensus. Granted, low contrast ratio, low image brightness, and motion can mask pixel definition in varying degrees. However, I have little problem detecting pixel structure at much closer than three screen heights (1.78:1 aspect).

http://www.poynton.com/PDFs/HDTV_Desktop_Computing.pdf
http://www.ndt-ed.org/EducationResou...sualacuity.htm
http://webvision.med.utah.edu/book/p...visual-acuity/
http://www.audioholics.com/education...f-human-vision
http://www.nhk.or.jp/digital/en/tech.../ibc200502.pdf
http://tech.ebu.ch/docs/techreview/trev_308-hdtv.pdf
http://archiv.arri.de/4kplus-systems/index.htm

Rather than listening to all the written literature on the subject. I did something novel. I displayed the checkerboard patterns (pixel phase) on Joe Kane's DVD HD Basics disc. I confirmed that the pixels in the single-pixel (1x1) area of the pattern were as clean and clear as the projector could make them from about a foot from the screen. I couldn't see individual pixels while wearing glasses that correct my vision to 20/15 until about 46 degrees. While 20/20 vision (different glasses or no glasses depending on the distance from the screen) was about 50 degrees. Results with panels is a little trickier because the 3 colors per pixel aren't coincident.

Human vision insn't an off-on thing... changes happen gradually for the sorts of things we're talking about here.

At these close viewing angles, the superiority of 4K projection is visible in the form of smoother edges on lines that are anything but perfectly vertical or horizontal. When using an HD source (Blu-ray) 4K projection removes enough aliasing that you see smoother edges. But when using conventional HD projection for the same sources, those same edges aren't obviously aliased... I can't see stair-stepping or anything else you would think should be obvious at a close viewing angle. But when it is GONE... yes, edges look smoother. Does that mean I'm seeing individual pixels with close viewing distances? It depends on your definition... your "standards". For me, 30 degrees is wildly too far from the screen for HD projection of HD images. Highly compressed images (satellite TV in my case) are still acceptable at the close distances... but I do see image defects clearly - though not ALL image defects. Many block defects require getting even closer to the screen to see them. Letterman & Leno look pretty good until I get closer... that reveals TONS of block artifacts. But because the contrast between edges of the block artifacts is low, it is difficult or impossible to see them with any acuity at 45-50 degree viewing angles. The compression block artifacts tend to NOT cross edge boundaries. So the blocks in a man's suit or pants or shirt or woman's dress or legs or arms are so low in contrast it masks their visiblilty. And those block artifacts are MUCH larger than single pixels.

Sometimes the theory just doesn't match the real-world viewing experience.

That said, I'd probably have to sit at something like 30 degrees for edges produced from Blu-ray on an HD projector to look as smooth as they do from a 4K projector (showing HD material) in the 45-50 degree range. BUT... that doesn't mean I'm actually seeing individual pixels in the 45-50 degree range for Blu-ray via an HD projector... I'm in that "gray" range where the edges of the characters on the eye chart may not be perfectly sharp, but they are still easily readable. And especially in MOVING images... what applies for still images like an eye-chart, once the images start moving and frames are changing at the rate of 24 or more times per second... perception is different unless you are projecting still images.

Blu-ray images from HD projection don't look like the edges are anything less than sharp at closer distances/larger angles until you have the 4K reference to compare them to.

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post #19 of 25 Old 05-13-2012, 07:07 PM
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Just another question on bias lighting.

my plasma is setup as pictured below, and the bias light as it reflects off the wall measures 35FtL (i1D2) above the centre of the display.
The display itself pumps out a peak of about 60FtL (it's a bright room)

What's the recommended ideal ratio or level of bias light to panel brightness?

My thought process begins with the fact that the accepted standard for viewing a plasma in a dark room is about 35FtL.
so in the ideal case where ambient is 0FtL, the screen is 35FtL above the ambient Light level.
given my panel output of 60FtL and my Bias of 35FtL, the difference is around 25FtL
which seems reasonable to me as being halfway between the optimal output of a Projector and a Plasma.
And the portion of wall behind the TV (between windows) that's illuminated by the light is probably a similar area to a ~90" screen.

Anyone else follow/ agree/ disagree with my logic (?)

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post #20 of 25 Old 05-13-2012, 07:40 PM
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Quote:
Originally Posted by Robbks View Post

Just another question on bias lighting.

my plasma is setup as pictured below, and the bias light as it reflects off the wall measures 35FtL (i1D2) above the centre of the display.
The display itself pumps out a peak of about 60FtL (it's a bright room)

What's the recommended ideal ratio or level of bias light to panel brightness?

My thought process begins with the fact that the accepted standard for viewing a plasma in a dark room is about 35FtL.
so in the ideal case where ambient is 0FtL, the screen is 35FtL above the ambient Light level.
given my panel output of 60FtL and my Bias of 35FtL, the difference is around 25FtL
which seems reasonable to me as being halfway between the optimal output of a Projector and a Plasma.
And the portion of wall behind the TV (between windows) that's illuminated by the light is probably a similar area to a ~90" screen.

Anyone else follow/ agree/ disagree with my logic (?)


It's best not to guess. Get the facts from the "sticky" threads in the 'Links to this forum's popular threads' section at the top of this area of the forum:

'D65 Video Bias Lighting- Fundamental Theory And Practice'
http://www.avsforum.com/avs-vb/showthread.php?t=1162578
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post #21 of 25 Old 05-13-2012, 07:48 PM
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thanks George.
I'd read that and somehow missed point #5

5. The brightness of the reflected illumination should be 10% or less of the brightest white the monitor is adjusted to (calibrated for a dark environment).

Given that, mine is a bit (lot) too bright.
I have a smaller version (half length tube) of the same light, that i'll install and measure.
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post #22 of 25 Old 05-13-2012, 07:58 PM
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Quote:
Originally Posted by Robbks View Post

thanks George.
I'd read that and somehow missed point #5

5. The brightness of the reflected illumination should be 10% or less of the brightest white the monitor is adjusted to (calibrated for a dark environment).

Given that, mine is a bit (lot) too bright.
I have a smaller version (half length tube) of the same light, that i'll install and measure.

yeah, that is way too bright; bias lighting should create a dim surround
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post #23 of 25 Old 05-13-2012, 08:35 PM
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in practice it's not "that" bright
especially as my eye level is only as high as the centre of the screen.
and as you can see the light falls-off quite rapidly.

i'll work out where on the rear wall i can actually see and measure to that point.

I'm definitely sold on it for reducing eye strain though.
I have a pretty bad astigmatism in one eye and some lazy muscles that get worse in dark environments (causing the entire eye to wobble from side to side) so a higher ambient light level helps to make the images clearer to my eyes.

(off topic) doing an eye test in a dark room with only the chart illuminated makes my vision around 2-4 lines worse than in a dimly lit room.
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post #24 of 25 Old 05-13-2012, 09:06 PM
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Originally Posted by Robbks View Post

in practice it's not "that" bright
especially as my eye level is only as high as the centre of the screen.
and as you can see the light falls-off quite rapidly.

i'll work out where on the rear wall i can actually see and measure to that point.

I'm definitely sold on it for reducing eye strain though.
I have a pretty bad astigmatism in one eye and some lazy muscles that get worse in dark environments (causing the entire eye to wobble from side to side) so a higher ambient light level helps to make the images clearer to my eyes.

(off topic) doing an eye test in a dark room with only the chart illuminated makes my vision around 2-4 lines worse than in a dimly lit room.

There seems to always be exceptions to the norm. The conventional recommendations are a good foundational starting point. Yours is an excellent example of how people are different and may require modification of the general practice to suit an individual.
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post #25 of 25 Old 05-13-2012, 09:14 PM
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Yeah, i may find that there's just not quite enough ambient light (my dog is black, she disappears into the floor when it's dark and is easily stepped on )

But I do like to start with a recognised standard and adjust to preference with some BTB testing of different options from there.
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