It’d make sense to think of TVs in terms of pixels, of how many dots they use to make a picture. No surprise there; it’s how TV makers pitch them—“high definition,” “4K,” and so on all refer, however obliquely, to dots per screen. But the standards that describe a TV screen’s capabilities also account for the range of possible colors it can display. That’s called a gamut, and it’s essentially a function of the ability of the light-emitting diodes that comprise that screen to put out light—both white light, for brightness, but also colors. The specific technologies vary in small ways, but the key is that the TVs output three colors: red, green, and blue. By varying the levels of each, the screens can emulate millions of colors, and human eyes and brains can’t tell the difference between those mixtures and a pure wavelength. Equal amounts of red and blue look the same, for example, as a straight-out violet.But just because a TV can output a tremendous number of different apparent colors doesn’t mean it can output all the colors. In the 1970s a researcher named MR Pointer actually set out to account for all the colors reflected by the surfaces we humans see—a very different problem than the colored lights a screen might emit, but hold that thought. So Pointer combined a bunch of different databases of color (of flowers, dyes, and so on) and mapped them onto the theoretical space of all possible colors in the visible spectrum, the thin slice of electromagnetic energy that human eyes can register and human brains can process. Pointer found that the colors humans actually encounter in nature are in fact a subset of the colors that eyes and brains can handle. But more importantly for our purposes, he found that televisions at the time sucked.The natural world had a gamut; televisions in 1980 had a narrower one. Today’s 4K TVs generally use light-emitting diodes either tuned to the right wavelengths or filtered in clever ways; back when Pointer was at work, the TVs used colored phosphors to emit light. But that set-up, even today, can only hope to create something like 90 percent of the colors humans can actually see. Those three emitters make the corners of an imaginary triangle that can lay on top of the perceivable colorspace; everything outside the triangle is a color that humans with color-normal vision can see, but that a television can’t produce. “In terms of chromaticity there are two areas of colour that are inadequately covered: high-purity green and green-blue colours, and high-purity red, magenta, and purple colours,” Pointer wrote in 1980. But on the other hand, he added, the blue phosphor was so good that “it falls outside the real-colour gamut.” It was more blue than blue.Televisions have gotten a lot better since 1980, obviously. The original high-definition color standard captured a relatively small triangle of the human-perceivable color gamut. So-called Ultra High Definition, or UHD (called BT.2020 in tech-speak) gets bigger. Still, there’s no way around the truth here: Color televisions show color, but they don’t show all the colors.Which brings me back to fireworks. They work because of the way certain elements deal with energy. Basically, if you pump energy into their atoms—in this case in the form of heat, from the fire part of fireworks—that energy gets absorbed by the electrons that orbit the atomic nucleus. But they can’t hold onto that excess juice, so they re-emit it—as photons, which is to say, light. And different atoms emit photons with different amounts of energy. Strontium pushes out red. Barium makes green. Sure, the mixes get more complicated and different recipes (and different shapes of explosive) give you different effects.You can overlay those basic colors onto the map of all the possible colors, and onto the triangle of the BT.2020 gamut. That’s what Allison Harn of the quantum dot company Nanosys did a few years back for a blog post. And the results were … not great. An older high-def gamut just barely managed to capture the true hue of bluish copper chloride. Orange-y calcium chloride was just outside the triangle. Green barium and red strontium, though? Forget it.UHD, the newer version, only did a bit better. The intense green and red of fireworks are still outside the gamut. The TVs would replace them with the closest available color they were capable of. So if you watched fireworks on your home display, you didn’t see their actual colors. You saw your TV’s best effort. No real surprise there. Good as it is, “BT.2020 is still only about 75 percent of human color vision,” says Poppy Crum, chief scientist at Dolby Laboratories.But all is not lost. Don’t let darkness overtake you. Or rather, do, because it may well be that light and dark are what’ll save us here, rather than some kind of theoretical expansion of the colorspace. That’d be “high dynamic range,” or brighter whites and darker, inkier blacks. Now, for sure, UHD TV makers tout excellent dynamic range already, but nominally lifelike whitest whites and blackest blacks remain challenging to the highest-end televisions. But Crum thinks they’re the secret to more intense and realistic color experiences—and they also happen to be a key to the next standard, BT.2100. She describes being able to see the metallic, explosive sparkle of pyrotechnic light against a deep black nighttime sky as “transformative.”Sadly, if you want the full patriotic red-red, white-white, and blue-blue experience for this year’s Fourth, you’ll still have to go outside and use your meatbag eyeballs and the clump of neurons behind them to get it. But maybe by the time this holiday rolls around again, BT.2100 TVs will be big on the market. And in between now and then, there’s another almost equally patriotic holiday that might help you get one, if you’re inclined to let your money get pulled in that direction. Around here we call it “Black Friday.”
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