Why do the TV’s here in America have the black level set at 7 IRE? I know in Japan they’re set to 0 IRE. Does anyone out there even know what I’m talking about?
The only theory I can come up with is that the average American is a complete moron, and needs to see his/her TV always somewhat lit to know that it’s working.
I must be a “complete moron” because I have no idea what you’re talking about.
Tell us 'bout IRE, mon.
First of all, American TVs have the black level set at 7.5 IRE. Second of all, you seem to be confusing the black level with the blank level with your “TV always lit” comment. The blank level on US TV monitors is still 0. If it wasn’t, you’d be able to watch the electron beam sweep across the screen during the retrace. It’s also why closed captions appear to show up in a black box; it isn’t black, it’s blank, which is darker than the 7.5 IRE black level.
As to why, beats me. Both the US and Japan use NTSC, but I believe they use two different sets of the standards. Hopefully, Cartooniverse or someone else in the industry will weigh in.
It stands for Institute of Radio Engineers. It’s a long story as to how it became a unit of measurement so I wont go there. Anyhow, it’s a measurement of line level video. If your video is at full brightness your at 100 IRE (so yeah it’s kind of a percentage), but here in the U.S. total black is 7 IRE, that’s why if you have all the lights off in your house a black screen will still (mildly) light up the room.
Sorry for not specifing, but since I work with video equipment all day, I’m used to the “Techy” lingo.
Ahem . . . (tap, tap) . . . Is this thing on? Once more, with feeling, with a cite. (Emphasis added.)
"The NTSC video standard has been around since 1953. While it still does a good job of getting pictures from one place to another, it has a few quirks which are a result
of the technological and practical limitations of that era.
One of these quirks is something called ‘black level setup’, or just ‘setup.’ Basically, it means that the black level is higher than the blanking level by 7.5 IRE.
If that last sentence sounds like gibberish to you, here’ s a quick explanation: video levels are measured in units called IRE, which stands for Institute of Radio
Engineers (go figure). Higher IRE numbers mean more brightness. White is defined as 100 IRE, so you would think that black is defined as 0 IRE. Not quite. Black is 7.5
IRE. 0 IRE is the called the ‘blanking’ level.
Blanking is the part of the video that happens signal during the retrace of the picture tube scan, when the electron beam is moving back to the left-hand side of
the screen to get ready for the next video line (or to the top of the screen, in readiness for the next frame).
The blanking level is blacker than black to make sure that the retrace is not visible on the screen, just in case the TV’ s adjustments aren’ t set perfectly (and in 1953, they usually weren’ t). With some older TV sets, you can crank the brightness and contrast all the way up and see the diagonal retrace lines."
And from here:
“The NTSC system dictates that black level be at 7.5 units IRE. This is due to historic problems in transmission. If the black level is too close to the blanking level, signals can drift and interfere with one another.”
So, this establishes that I was in fact correct that US NTSC black level is in fact 7.5 IRE, not 7, and that it was for the reason I stated – to prevent visibility of the beam during retrace at the end of the line or the bottom of the screen. Cripes. If you work around video equipment all day, you should know that.
A turned-off set might slightly illuminate a darkened room for a few minutes after it is turned off, but in general, it most certainly will not. I can attest to this with absolute certainty because I often sleep in the living room (due to a little snoring problem of my wife’s), and with our 32" set off and the curtains closed, the room is pitch black.
Now, in this PDF file from Pioneer, we learn that:
"In the original black and white American TV system, Absolute Black Level was a video signal of 0 volts DC. It is now known, 0.285 volts, or 40 IRE, (units of video
defined by the Institute of Radio Engineers, 140 IRE = 1 volt, 100 IRE above 0 volts, 40 IRE below 0 volts) of the total 1 volt video signal exists below that black level
(now known as blanking level).
**The -40 IRE will completely shut off the electron beam during the horizontal and vertical retrace intervals. When color came to NTSC in 1953, the level of picture black was raised to +7.5 IRE. The higher level of black was necessary because early black and white transmitters could not handle a color signal with black level at 0 volts.
The NTSC system still places black level at +7.5 IRE. Japan abandoned the +7.5 IRE of NTSC in 1990.**"
So, the question then clarifies itself – why did Japan move to a Setup level of 0 IRE in 1990 but the US did not? Here we find a partial answer:
“In the original black and white television system the voltage level for picture material at black was zero Volts DC or 0 IRE . . . The level for white was 716 millivolts or 100 IRE. When color first came to NTSC it became necessary to raise the level of black to +7.5 IRE, compressing the dynamic range between black and white. By the time all three networks had gone to color in 1964 the +7.5 IRE black level was no longer necessary, but the rule wasn’t changed. In 1990 there was a push in the program production industry to change it back to 0 IRE. That change actually took place in Japan but didn’t happen here in the United States. Part of the push for the change came from the fact that a lot of program material was being produced in the SMPTE component video domain which uses 0 Volts for black. The majority of DVD’s are mastered using 0 Volts DC for black. In reality all DVD’s should be mastered using 0 Volts DC for black, but there are exceptions. The dynamic range of the component video picture is enhanced relative to the standard composite NTSC color system. The DVD player will reduce that dynamic range, moving it from 0 IRE to + 7.5 IRE, in providing an NTSC output which is necessary for compatibility with standard home display devices.”
I suspect it has something to do with the fact that Japan tends to have consumer video technology that is a little bit ahead of the curve of that in the U.S., and thus are able to manufacture compatible output devices and monitors that will accept a black level of 0 IRE. As it is, if you have a DV camcorder, it uses a black level of 0, as do DVDs (as mentioned above). A lot of DVD players will let you preserve the 0 IRE level for output.
This report from the Japan Economic Institute appears to lend credence to my theory: Japan changed their black level because of their advances in electronics and HDTV broadcasting. Their public broadcaster NHK, according to the report, was by 1991 broadcasting 8 hours a day in HDTV. US broadcasters have only been sending HDTV signals for, what, two years? I suspect that over the next few years, US televisions will adopt the same standard, especially as the move towards full HDTV broadcasting occurs.
Holy MOLEY !!! What could I possibly add to the amazingly thorough research done by pldennison???
<—bowing down on knees, " I’m not worthy ". 
I’m not a member of SMPTE for a GOOD reason. My take would be, " Yo, Billy, these blacks are for shit, I’m lighting it to death and it still looks like German Expressionism. Help me out here, huh?"
Billy would then throw a few switches and curse me roundly.
The real reason, of course, is that NTSC stands for Never The Same Color. 
At the studio where I used to work we had a signal generator that would give you an arbitrary amount of luminence (sp?) which you could set with a dial. Naturally we were taught to set it to 7.5 IRE for laying down control track on virgin tapes before editing, but there were always people who set it to 100 just to be obnoxious.