Re the day/night changing ambient light question, discussed at some length in the interview...
My solution to that is just to leave some extra elbow room in the white level adjustment to compensate for changes in room lighting and also variations in the brightness of video content, and to keep some basic video setup patterns for levels adjustment handy on a USB stick (so I don't have to swap discs to do some black/white level tweaking during the day). Included in my patterns are a set of ambient references, which are simply flat field grays of varying brightness. And there are also the usual Pluge/black level tests and some white level tests to make sure highlights aren't too stressful on my eyes.
Most of my viewing is done at night though in controlled lighting, so the main calibration on my TV is adjusted primarily for that. And all of those adjustments are done in the TV's service mode with the User settings at the middle/default values, so I can easily "snap back" to my night calibration after tweaking the User controls (ie Picture/Contrast, Brightness) during the day.
You probably won't find a whole lot of info here or elsewhere on using ambient references for white level adjustment btw (except in some of my other posts in the calibration forum), because it's not part of the normal canon of calibration that most pros use. (Most calibrators are the "set it and forget it" type.) But I've had pretty good luck with it, and would encourage others to at least consider experimenting with the idea. In the final analysis though, your eyes are probably always gonna be the best judge of what's too bright and what's not, and patterns for that kind of thing can only get you so far. So this is just one other tool among many to maybe aid a little in making those assessments.
Here's the "short" version of how an ambient reference works...
For mastering video content, SMPTE suggests keeping the ambient/surround levels to less than 10% of the display's white luminance. What that means is that the area behind and around the TV should be no brighter than an ~35%* stimulus gray on the TV screen.
Through alot of trial and error though I've found that a gray somewhere around the middle of the 0% to 35% stimulus range is a pretty good reference for the brightness of the surroundings around my TV. For most direct-view TVs (LCD, plasma, LED, CRT), you generally wouldn't want the surround levels to be as dark as 0% stimulus (ie black) on your TV, because: a) the brightness of the TV would be a strain on the eyes, and b) the blacks wouldn't actually look "black" on the screen. And most video content (computer/web content may be dfferent) will tend to look rather dim and lifeless if the surroundings are as bright as a 35% gray. So it makes sense that a value approximately in the middle of that 0% to 35% range should give pretty decent results.
An ~15% stimulus gray reference (give or take about 2.5%) tends to work pretty well for me both at night and during the day. I adjust the white level on my (CRT) TV, so that a 15% flat field gray is a pretty good match to the overall surround levels in my viewing area behind and around the TV, and then tweak from there if needed. If your TV doesn't have the deepest blacks though, then you might want to try a slightly brighter reference, perhaps more in the 17.5% to 20% range (esp. to "help out" the blacks for night viewing). I keep a variety of different gray levels handy on my USB setup stick btw. And the best approach is probably just to experiment until you find a gray/ambient reference which is most comfortable for your eyes.
According to some sources, the APL (average picture level) of video over time is ~15%, which may be why that seems to work pretty well with my CRT. There's alot of variation in the brightness of video content though, so depending on what you watch, that may or may not be a good range. The APL of computer content is closer to ~35% btw, so if you use your TV mostly for web-browsing and other computer apps, then using an ambient reference more in the 35% range would not be unreasonable.
The ambient reference works both ways btw. You can use it either to adjust the brightness of the room lighting, or to adjust the white level on the display, whichever makes the most sense in your particular setup.
Changing the white level on your TV for day viewing may also have some effect on the color balance of the TV's grayscale. So if you do alot of viewing during the day and also at night, you might want to keep track of the approximate white levels used for both, and do the grayscale adjustment with the white level control set somewhere in the middle of that day/night range.
(*On a typical TV with gamma in the 2.2 to 2.4 range, a 35-40% stimulus gray will have approximately 10% of the relative luminance of white. 0.35 raised to the power of 2.2 equals ~0.10. I use 35% here because that's the value of the maximum ambient reference on the old Digital Video Essentials disc, which is what most people here are probably familiar with.)
Edited by ADU - 4/11/13 at 1:22pm