So, You Think You're So Bright?
I’m often amazed, and sometimes confused, by the way certain words have entirely different meanings depending on the subject matter. For example, compare the statement, “she’s much brighter than her brother,” to “flat-panel TVs are much brighter than projectors.” In the first case, “brighter” most likely means more intelligent, while in the second case it means…what exactly? Does it mean that the light output from most flat-panel TVs is higher than the light output from most projectors? Or that most flat-panel TVs are easier to watch in a well lit showroom than a projected image?
It’s not clear—because the term “brighter” doesn’t have a fixed meaning when comparing these two types of displays. It’s a subjective term based on a perceptual value that varies based on several factors—including the adaptation level of the viewer’s eyes, the field of view occupied by the displayed image, and the ambient lighting conditions around both types of display. All of these factors (and a few less important ones) may help to explain why you’ll never hear someone say, “Wow, watching that blockbuster movie on your new TV was so much better than watching it in the theater!”—unless they are referring to the comfort level of the seating. (One of my main complaints about most movie theaters.) [Editor's note: ...Or referring to the quality of the sound system...but that's a discussion for another day!—R.S.]
If you were actually able to measure and compare the light output from both types of displays using a luminance meter (an objective measurement), then flat-panel TVs would typically show much higher maximum luminance values on screen. So changing the statement to “flat-panel TVs have higher light output than projectors” may be more accurate. But it still doesn’t give them an advantage over projectors. For starters, our eyes automatically adapt the average luminance of the scene occupying our field of view, which is why shining a flashlight in someones eyes at night has a different effect than shining that light in their eyes on a sunny day. As a result of adaptation, images projected on screen in a darkened theater can appear similar in “brightness” to those displayed on a flat panel TV in a room with much higher ambient light levels.
The field of view (FOV) occupied by each display type also plays a part. In a darkened projection home theater or commercial movie theater, the screen usually occupies a much larger field of view (assuming you get the good seats!) than the FOV occupied by a flat-panel TV viewed from the couch in your family/entertainment room. Of course, it’s possible to turn down all the lights in your TV room in order to match the ambient lighting levels of a theater, and you can also move closer to your TV until it fills the same FOV as a large movie theater screen. But if you’ve ever done so, especially with a large flat-panel TV, you’ll notice how quickly your eyes tire from excessive TV glare and contrast...unless you turn the TV to its dimmer movie mode or increase ambient light levels. That’s soft proof that flat-panel TVs and home theater projectors are designed for different viewing environments—but with the same goal in mind: to match the content creator or director’s intent as closely as possible within the display’s capabilities.
The movie industry has long understood the importance of the factors just discussed since it makes money selling movies to both theater goers and TV owners. That’s one of the reasons why SMPTE (one of the standard associations helping to regulate the movie industry) has set specifications for projectors and the viewing environments found in commercial theaters. For example, for a general commercial theater (regardless of screen size), SMPTE recommends a projector be able to fill the screen with a peak luminance of 48 cd/m2 (equivalent to 14 ft lamberts, or 48 nits), and a minimum black of 0.03 cd/m2. In this case, a min black of 0.03 on screen requires a very dark room with minimal amounts of ambient light spilling on the screen. In a high-end “reference” or color-grading projection environment, SMPTE requires the same max luminance of 48 cd/m2along with a darker 0.01 cd/m2 min black on screen (only possible in a super-dark environment). Interesting to note that those specified theater luminance levels equate to a measured ANSI contrast ratio (not full off/full on) between 1,600:1 (general theater) and 4,800:1 (reference theater).
SMPTE has not yet specified screen and ambient luminance levels for commercial theaters using tiled flat panel TVs or microLED displays, possibly because neither technology is commercially viable due to extremely high initial cost and ongoing operational costs. However, for SDR (standard dynamic range) TV displays, the SMPTE and other related entities recommend a max luminance of 100 cd/m2 and an ideal ambient light level that is 5% of the TV’s max luminance (about 5 cd/m2). Those levels were based on older CRT screen technologies, so if you have a newer SDR TV it's probably capable of achieving 160 to 200 cd/m2 max luminance. If so, your ideal ambient light levels for viewing a movie on a new flat-screen TV will probably be between 8 and 10 cd/m2—which is 200 to 300 times brighter than the ambient light levels recommended for a commercial or home theater! Keep in mind that with flat-panel TVs, ambient light levels do not affect the min luminance levels as greatly as on a projected screen image, but higher ambient levels can cause reflections that reduce contrast and overall image quality.
The bottom line is that brightness is a subjective term that shouldn’t be used to compare different display types, or even similar display types. Of course, I don’t expect retail A/V salespeople to shift over to saying “flat panels have higher luminance levels than projectors” any time soon—it would take too much time to also explain to potential customers that even measured luminance and contrast ratios for a given flat panel display can’t really be used to compare it to a home theater projector without first taking into account the different viewing conditions recommended for each type of display.
Now that the competition between HDR flat panels and HDR home theater projectors is heating up, it’s going to get even trickier. The main reason? Standards organizations such as SMPTE have not locked down their specifications for HDR projectors for use in commercial theaters. Currently, the in-fighting between HDR-display and projector companies trying to standardize on their specific technologies and advantages is fierce. This may explain why there are still fewer than 100 HDR-capable theaters in the U.S. despite the proven image quality advantages of HDR. Until those standards are in place, few theater owners will be willing to invest in new projection equipment or the support systems needed to handle HDR movie content—including massive storage systems, increased bandwidth within the theater and for downloading movies from suppliers, and more stringent copyright security protocols. This means that, for the first time, you can purchase an affordable HDR home theater projector today that delivers a higher quality image in your own home than they can get in most commercial theaters. And the popcorn costs less too!