Bias Light
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Joined: Feb 2009
Posts: 3,466
connoisseur
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OP
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I've mentioned a few times that I have a "bias light" behind my screen, and that everyone else should too. I've attempted to photograph how it affects the image, but because of what the bias light is actually doing, i.e. providing a reference for the eye, the camera is not fooled as easily. A bias light does two major things: One, it provides a reference white (provided you have neutral colored walls). Human vision tend to compensate for the color of lighting. You'll still see an egg as being white even under a purely red light. A scene in a movie that's lit by a red light will have less visual impact as your eyes will adjust. A constant 6500K reference will make the colors on screen appear more true. Two, it keeps a base level of lighting in the room. Watching a screen in complete dark will cause a constant change in the pupil where a dark scene will make a following bright scene wash out. So some room light is required, but if the light is in front of the screen it can wash out the display, and highlight other objects near the display. This first image is taken with the over-head room light on. All the bulbs in my apartment are 5900K, 5-phosphor, CFL, with a CRI of 93. They're very good bulbs, almost as good as the bias light. I white balanced on the wall behind the screen. The second image is with the lights out. This time I went with an auto-white balance as that's what your eyes would be doing without any other reference. This shot is lit by the bias light located behind the TV. Again the white balance is on the wall. This light is a florescent tube, with a color temp of 6500K, and a 7-phosphor coat, with a CRI of 96. This is a bulb used to color proof commercial goods in a viewing booth. Also notice how you can no longer notice the speaker or the PS3. The rest of the room is equally dark. What I couldn't simulate is the slow reaction of the eye's iris to changing lighting conditions in a film. If you want a better idea of the subtle differences between the shots, open them in separate tabs and switch back and forth. Notice especially with the first and last that the walls appear to be the same neutral white, but the color on the display becomes more saturated with the bias light shot. There's also something cozy about a soft glow emanating from behind the TV.
Pioneer PDP-5020FD, Marantz SR6011 Axiom M5HP, VP160HP, QS8 Sony PS4, surround backs -Chris
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Re: Bias Light
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Joined: Dec 2003
Posts: 10,420
shareholder in the making
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shareholder in the making
Joined: Dec 2003
Posts: 10,420 |
Intersting, thanks. I may have to do something like this for the new room.
Jason M80 v2 VP160 v3 QS8 v2 PB13 Ultra Denon 3808 Samsung 85" Q70
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Re: Bias Light
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Joined: Sep 2004
Posts: 11,458
shareholder in the making
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shareholder in the making
Joined: Sep 2004
Posts: 11,458 |
Ray3 was always a big fan of bias lights if I remember correctly....
::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::
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Re: Bias Light
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Joined: Dec 2003
Posts: 6,331
axiomite
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axiomite
Joined: Dec 2003
Posts: 6,331 |
I use an Ideal-Lume standard, 6500k bias light behind my TV. Wouldn't watch without it.
Jack
"People generally quarrel because they cannot argue." - G. K. Chesterton
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Re: Bias Light
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Joined: Apr 2007
Posts: 4,877
connoisseur
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connoisseur
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-David
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Re: Bias Light
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Joined: Oct 2006
Posts: 6,955
axiomite
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axiomite
Joined: Oct 2006
Posts: 6,955 |
Very interesting. I have never heard of this effect.
Is the type of light the bulb produces the key or the fact that it is located behind the TV the most important item or both?
With great power comes Awesome irresponsibility.
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Re: Bias Light
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Joined: Jul 2006
Posts: 12,077 Likes: 7
Founder, Axiom Upgrade Club shareholder in the making
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Founder, Axiom Upgrade Club shareholder in the making
Joined: Jul 2006
Posts: 12,077 Likes: 7 |
Also, is anyone doing this for projection screens, or is it only TVs?
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Re: Bias Light
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Joined: Feb 2009
Posts: 3,466
connoisseur
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OP
connoisseur
Joined: Feb 2009
Posts: 3,466 |
I use the Ideal-Lume Pro, but that's probably overkill. I had a Standard before, and really can't tell the difference.
The TV is a Pioneer PDP-5020FD, 50" plasma.
Placing any light behind the TV to give about a 15% gray value to the surround wall is enough to bias the eye's iris, and improve perceived contrast. The reference 6500K white with a very high color rendition index, biases the white balance of the eye to make the hues read more correctly.
Pioneer PDP-5020FD, Marantz SR6011 Axiom M5HP, VP160HP, QS8 Sony PS4, surround backs -Chris
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Re: Bias Light
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Joined: Feb 2009
Posts: 3,466
connoisseur
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OP
connoisseur
Joined: Feb 2009
Posts: 3,466 |
Also, is anyone doing this for projection screens, or is it only TVs? Projection screens are big enough to fill the field of view that is it hard to make use of a border to bias the eye. I've also read that the larger the screen the less it is needed. But going from 32" to 50" didn't decrease the effect to me.
Pioneer PDP-5020FD, Marantz SR6011 Axiom M5HP, VP160HP, QS8 Sony PS4, surround backs -Chris
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Re: Bias Light
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Joined: Nov 2008
Posts: 1,789
connoisseur
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connoisseur
Joined: Nov 2008
Posts: 1,789 |
Wasn't there a Panasonic or Sony TV that came out not too long ago that radiated light behind the set? Only as I remember it, it wasn't a white light, it would radiate the main color on the display at the time, so it was constantly changing. In the commercial they touted the back light as making the whole experience more involving of the viewer. However it seems they missed the whole purpose of it if they were using colored lights instead of a constant white source like you are.
Very interesting indeed.
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