30 or 35 fL ideal for a completely dark room? - AVS Forum
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post #1 of 16 Old 08-03-2011, 06:11 AM - Thread Starter
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Is 30 or 35 fL ideal for a completely dark room for a direct view display? Which is better for a room with no ambient light? What about gamma? Is 2.2 still recommended in these conditions?
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post #2 of 16 Old 08-03-2011, 06:43 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

Is 30 or 35 fL ideal for a completely dark room for a direct view display? Which is better for a room with no ambient light? What about gamma? Is 2.2 still recommended in these conditions?

I think it depends largely on how and WHAT you're measuring. There are often a lot of variables here, but for a pitch black room, 30 fL should be plenty on a direct view display. There isn't a hard & fast rule about this. Try it out and see when it begins to hurt your eyes. 35 fL would probably be a tad much in a completely dark room without any bias lighting but you'll have to experiment a bit.

Is it a plasma? If so, be careful that ABL isn't kicking in or you won't get a true fL reading. For example, measure it with standard windows and then measure it again using the small APL windows. On my VT30, the small APL windows yield a higher fL reading indicating that the standard windows are affected by ABL. What I don't know is if the small APL windows are affected by ABL as well.

In Cinema mode on my VT30 using an i1 Pro:
Small APL = 27.7 fL
Standard Window = 23.7 fL

I don't have my readings from my i1D2 handy, but I want to say that the fL readings differed by several points, so it will depend on the accuracy of your meter for luminance readings as well.

That said, assuming the i1 pro is "reference", Cinema mode is plenty bright in an all black room. I'm not sure if ABL is kicking in at all on the small APL windows however, so I'm not sure 27.7 fL is truly accurate. It could be a few points higher.
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post #3 of 16 Old 08-03-2011, 06:50 AM - Thread Starter
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Quote:
Originally Posted by jkozlow3 View Post

I think it depends largely on how and WHAT you're measuring. There are often a lot of variables here, but for a pitch black room, 30 fL should be plenty on a direct view display. There isn't a hard & fast rule about this. Try it out and see when it begins to hurt your eyes. 35 fL would probably be a tad much in a completely dark room without any bias lighting but you'll have to experiment a bit.

Is it a plasma? If so, be careful that ABL isn't kicking in or you won't get a true fL reading. For example, measure it with standard windows and then measure it again using the small APL windows. On my VT30, the small APL windows yield a higher fL reading indicating that the standard windows are affected by ABL. What I don't know is if the small APL windows are affected by ABL as well.

In Cinema mode on my VT30 using an i1 Pro:
Small APL = 27.7 fL
Standard Window = 23.7 fL

I don't have my readings from my i1D2 handy, but I want to say that the fL readings differed by several points, so it will depend on the accuracy of your meter for luminance readings as well.

That said, assuming the i1 pro is "reference", Cinema mode is plenty bright in an all black room. I'm not sure if ABL is kicking in at all on the small APL windows however, so I'm not sure 27.7 fL is truly accurate. It could be a few points higher.

It's an LCD and the main reason I'm asking is because there's a tradeoff between brighter whites or deeper blacks (backlight setting).
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post #4 of 16 Old 08-03-2011, 07:03 AM
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Many grading rooms run their monitors at about 100 nits (29 foot lamberts). I don't know about gamma though.

My man cave is totally light controlled and my 75" LaserVue outputs about 20fl and 2.3 gamma. The total light output with that many square feet is just about right, ie., I wouldn't want any more.

Edit: I use bias lighting as well.

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post #5 of 16 Old 08-03-2011, 07:45 AM - Thread Starter
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Interesting, this source says: "SMPTE has established standards for luminance of reference displays. This is 120 cd/m2 (35 fL) for flat panels."

THX also recommends 35 fL.
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post #6 of 16 Old 08-03-2011, 07:50 AM
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I know that industry standard is 35ftl. Its been posted and Ive seen it on smtpe pdf's.

But through experience and viewing I cant help but think there needs to be a better standard. One that includes Monitor size and seating distance.

For instance I can handle in the dark easily 50+ftl on a 20 inch screen in the bedroom from like 15 feet. If I tried to do that on my 60 from 11 feet Id fry my eyes out.

I start with 30ftl and then over time depending on lighting, distance, and screen size I adjust between 27 and 35ftl on my sets for easy viewing pleasure.
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post #7 of 16 Old 08-03-2011, 07:55 AM - Thread Starter
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Quote:
Originally Posted by serialmike View Post

I know that industry standard is 35ftl. Its been posted and Ive seen it on smtpe pdf's.

But through experience and viewing I cant help but think there needs to be a better standard. One that includes Monitor size and seating distance.

For instance I can handle in the dark easily 50+ftl on a 20 inch screen in the bedroom from like 15 feet. If I tried to do that on my 60 from 11 feet Id fry my eyes out.

I start with 30ftl and then over time depending on lighting, distance, and screen size I adjust between 27 and 35ftl on my sets for easy viewing pleasure.

I guess I should mention the display in question is a 32 inch and viewing distance is 4 ft.
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post #8 of 16 Old 08-03-2011, 08:59 AM
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I agree that there is at least something to the screen size/FOV and light output relationship... Many front projector setups look quite bright at 10 or 12 fL, but smaller direct views definitely need a lot more.
I've also found that, while I prefer a lower gamma between 2.2 and 2.28 on plasmas, the LED LCD sets I've calibrated recently need a higher gamma of 2.35-2.4 to match the same look of a plasma at 2.22. I had a Sammy PN plasma calibrated to 2.22, and I had to calibrate a Sammy UN LED to 2.4 to get them to look similar, with identical peak light output. I used small windows on the plasma.
I would try a light output of 35 fL and gamma of 2.4.
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post #9 of 16 Old 08-03-2011, 09:45 AM - Thread Starter
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Quote:
Originally Posted by Chad B View Post

I agree that there is at least something to the screen size/FOV and light output relationship... Many front projector setups look quite bright at 10 or 12 fL, but smaller direct views definitely need a lot more.
I've also found that, while I prefer a lower gamma between 2.2 and 2.28 on plasmas, the LED LCD sets I've calibrated recently need a higher gamma of 2.35-2.4 to match the same look of a plasma at 2.22. I had a Sammy PN plasma calibrated to 2.22, and I had to calibrate a Sammy UN LED to 2.4 go get them to look similar, with identical peak light output. I used small windows on the plasma.
I would try a light output of 35 fL and gamma of 2.4.

It currently looks like this. Should I still increase gamma?
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post #10 of 16 Old 08-03-2011, 09:51 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

Is 30 or 35 fL ideal for a completely dark room for a direct view display? Which is better for a room with no ambient light? What about gamma? Is 2.2 still recommended in these conditions?

Video industry standards bodies have recommended for decades the use of biasing ambient lighting for critical viewing of color television monitors operating at 30 to 35 fL. Their recommendations are based upon extensive human factors studies, plus the practical need in a mass communication medium for uniformity and repeatability of results in program mastering. Such uniformity can not be overemphasized if image fidelity and artistic integrity are valued. The validity and practicality of their recommendations have been borne out over decades of industry use. This "wheel" has not been shown to require reinvention.

It should be understood that viewing environment recommended practice is not officially considered a "standard" in the video industry. There are genuine standards that are quite specific and precise. Then there are engineering guidelines and recommended practices that are followed broadly in the industry because they work well. To deviate from recommended practice is not violating an official standard.

The origin of specifying peak white at 30 to 35 fL for critical viewing of a direct view monitor appears to be derived from a combination of human factors and the light output limitations of CRT displays (SMPTE RP166 and 167). In more recent years there have developed differing practices and recommendations relating to newer display technologies. Some variations have appeared in publications from the ITU, Poynton, etc., but SMPTE's work is still widely adhered to throughout the industry. Imaging technologies may change, but human factors will not.

It should also be understood that THX and/or ISF are not standards bodies. They are essentially consulting and training services that base their methodologies, specifications, and certifications on the same technical standards, engineering guidelines and recommended practices that govern the motion imaging industries at large.

As far as "brighter whites or deeper blacks" are concerned, the benefits of properly implemented bias lighting serve that purpose quite well, as explained in the following quotes:

"Contrast could be considered to be the most significant quality that impacts not only the perceived depth of an image, but also affects the apparent sharpness.....While the luminance level of a given image affects how the eye perceives contrast and detail, the ambient conditions surrounding the image can also have a dramatic impact. This phenomena was studied by Bartleson and Breneman (1967) to examine the impact of perceived contrast based not only on the luminance level of the image but taking into account the surrounding ambient luminance levels as well. Their results showed that the perceived contrast increased as ambient luminance increased. With the increase in ambient luminance, the eye interprets black levels as being darker while the impact to the white level is minimal. Since the perceived difference in dark areas is greater under the higher ambient luminance conditions, the perceived contrast is higher. It is a natural tendency to want low ambient luminance levels to strive for "better" perceived image quality and what is thought to result in higher contrast. However, in reality, the opposite is true. This tendency may be justified for current direct view CRT televisions due to the issue of glare that results from the glossy surface of the glass tube [also true for certain flat panel displays today]. With less ambient luminance, the glare is reduced- but it may be important to keep some ambient luminance behind the television [as in the case of bias lighting] to keep the perceived contrast higher.....While sharpness can affect the apparent contrast of an image, the converse is true in that contrast can also impact the apparent sharpness of an image. Images that have lower contrast will appear to be not as sharp as an image of the same content, but with higher contrast.....A subjective study was then conducted to verify the impact that ambient lighting has on perceived contrast. Several non-technical (and thus presumably non-biased) and technical observers were asked to compare a series of images with various ALL [average luminance levels] under different ambient luminance extremes in order to understand the impact that ambient viewing conditions might have on the perceived contrast between the two television technologies [CRT and DMD (DLP RPTV)]. Under dark ambient conditions, the result for images with an ALL > 5% was found to be equal between the CRT and the first DMD display. However, under bright ambient conditions (about 250 nits of luminance on the wall behind all of the units), the DMD display was favored over the CRT by 50% of the observers as having higher perceived contrast.....This proved that ambient conditions have the effect of potentially raising the black level threshold of the eye above the actual black level of the television such that the perceived contrast ratio is higher." from the SMPTE Journal, 11/02. 'The Importance of Contrast and its Effect on Image Quality' by Segler, Pettitt and Kessel

"Their experimental results, obtained through matching and scaling experiments, showed that the perceived contrast of images increased when the image surround was changed from dark to dim to light. This effect occurs because the dark surround of an image causes dark areas to appear lighter while having little effect on light areas (white areas still appear white despite changes in surround). Thus since there is more of a perceived change in the dark areas of an image than in the light areas, there is a resultant change in perceived contrast.....Often, when working at a computer workstation, users turn off the room lights in order to make the CRT display appear of higher contrast. This produces a darker surround that should perceptually lower the contrast of the display. The predictions of Bartleson and Breneman are counter to everyday experience in this situation. The reason for this is that the room lights are usually introducing a significant amount of reflection off the face of the monitor and thus reducing the physical contrast of the displayed images. If the surround of the display can be illuminated without introducing reflection off the face of the display (e.g., by placing a light source behind the monitor that illuminates the surrounding area), the perceived contrast of the display will actually be higher than when it is viewed in a completely darkened room." from 'Color Appearance Models,' by Mark D. Fairchild, Ph.D., of the Chester F. Carlson Center for Imaging Science: Munsell Color Science Laboratory

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post #11 of 16 Old 08-03-2011, 09:52 AM
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I would, unless your shadow detail takes too big of a hit.
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post #12 of 16 Old 08-03-2011, 11:09 AM
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for an LCD in a black room, I'd drop the back light as much as possible, the better blacks will be more noticeable than the brighter whites.

I'd probably go for like 80cd/m, which is usually right about where the backlight bottoms out.

In a room where sometimes the lights are on I'd go right back to 120-150, depending on lighting conditions.

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post #13 of 16 Old 08-03-2011, 11:50 AM - Thread Starter
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Originally Posted by Chad B View Post

I would, unless your shadow detail takes too big of a hit.

Does your observation hold true for CCFL-LCDs as well or just LED-LCDs? My TV is the former.
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post #14 of 16 Old 08-03-2011, 01:32 PM
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Quote:
Originally Posted by jkozlow3 View Post

I think it depends largely on how and WHAT you're measuring. There are often a lot of variables here, but for a pitch black room, 30 fL should be plenty on a direct view display. There isn't a hard & fast rule about this. Try it out and see when it begins to hurt your eyes. 35 fL would probably be a tad much in a completely dark room without any bias lighting but you'll have to experiment a bit.

Is it a plasma? If so, be careful that ABL isn't kicking in or you won't get a true fL reading. For example, measure it with standard windows and then measure it again using the small APL windows. On my VT30, the small APL windows yield a higher fL reading indicating that the standard windows are affected by ABL. What I don't know is if the small APL windows are affected by ABL as well.

In Cinema mode on my VT30 using an i1 Pro:
Small APL = 27.7 fL
Standard Window = 23.7 fL

I don't have my readings from my i1D2 handy, but I want to say that the fL readings differed by several points, so it will depend on the accuracy of your meter for luminance readings as well.

That said, assuming the i1 pro is "reference", Cinema mode is plenty bright in an all black room. I'm not sure if ABL is kicking in at all on the small APL windows however, so I'm not sure 27.7 fL is truly accurate. It could be a few points higher.

Interesting numbers. They are almost identical to those I ended up with when calibrating my 65" 600U; the VT35 of late 2006. Anything higher than 23-24 on a standard window caused noticeable clipping on the S&M disc. Equipment/software was a chroma 5 and ChromaPure Pro.
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post #15 of 16 Old 08-03-2011, 05:09 PM - Thread Starter
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post #16 of 16 Old 08-11-2011, 04:35 PM
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Quote:
Originally Posted by PlasmaPZ80U View Post

Interesting, this source says: "SMPTE has established standards for luminance of reference displays. This is 120 cd/m2 (35 fL) for flat panels."

THX also recommends 35 fL.

I think that 35fL figure is really intended for a dim rather than dark surround, and tend to agree with GeorgeAB's post above.

Not sayin they don't exist, but I've personally never encountered a conventional LCD with deep enough black levels to produce acceptable PQ in a totally dark surround. I wouldn't even watch a direct-view CRT that way. (If you own an LED with local dimming that can produce substantially deeper black levels on low APL scenes, that might possibly be more workable in a totally dark room than a conventional LCD.)

If you want blacks/shadow detail to actually look black rather than dark gray on your LCD, then I'd suggest using at least a little background illumination. For optimal viewing of typical home video content, I generally recommend surround levels close to the APL of video over time, or roughly in the neighborhood of an ~15% (nominally about 13% - 20%) stimulus gray on the screen. More here.

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