Taking a closer look at color-changing LEDs

Sure, these bulbs are smart -- but how accurate are those colors?

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If you've been looking into smartening things up around the home, then you've probably at least considered color-changing LEDs. The most prominent option out there is the Philips Hue LED kit, though we've also had fun playing around with the Lumen LED Color Smart Bulb from Tabu.

Both bulbs boast plenty of smart features. The Zigbee-powered Hue LEDs are compatible with IFTTT and SmartThings, while the Bluetooth-powered Lumen LED offers simple scheduling and fun features such as a native music-sync mode. But with all of the focus on smarts, it's easy to forget about the core functionality of these things. We wanted to know: are these color-changing bulbs actually good at changing colors?

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To test these bulbs out, we used a device called a spectrometer. The spectrometer is useful for comparing things like bulb brightness and color rendering in generic bulbs, but it's helpful for testing color-changing LEDs, too. After setting the bulbs to a certain color, we can use the spectrometer to measure just how accurate those colors are.

We started out by testing each bulb's ability to shine red, as compared with a basic red incandescent party light. As you can see on the chromaticity charts above, all three bulbs did a fine job, giving us results that plotted squarely in the graph's red-light district. The incandescent we used was only a 25-watt bulb, so it was noticeably dimmer than the LEDs, but brightness doesn't factor into chromaticity, so it didn't affect our results.

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We started to see some separation once we moved onto yellow light. The incandescent party light gave us something that skewed more toward orange, which is understandable -- a pure yellow "party" incandescent wouldn't make a whole lot of sense, as it wouldn't look much different from a standard incandescent.

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Remove the bulb from a Philips Hue LED, and you'll realize that the yellow diodes are the most dominant. Colin West McDonald/CNET

This tilt toward orange held true for the Lumen LED as well, though to a lesser extent. As for the Philips Hue LED, it did a much better job hitting a pure yellow, which likely has something to do with the fact that it has five yellow diodes compared with four red and two blue, making yellow the most dominant tone in the Hue spectrum. This helps the Hue when it comes time to mimic incandescent light -- more on that in just a bit.

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Our blue-light test was where we really began to see some major differences between the three bulbs. True blue resides down in the bottom-left nook of the chromaticity graph, and if you look at the graph for our incandescent party bulb, you'll see that it skews much further north, giving off more of a greenish-blue version of cyan. Not an unattractive light by any stretch, but not all that accurate, either.

Both the Lumen LED and the Philips Hue LED sit much lower in their respective graphs, putting them much closer to that perfect shade of blue. Look closely, though -- those two graphs aren't identical. The Lumen LED sits just slightly closer to blue than the Hue LED, which seems to cross over into purple territory. It's a small, subtle difference in the graphs, but how does it translate to the actual quality of the light?

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Colin West McDonald/CNET

Take a look for yourself. That's the incandescent party bulb on the left, the Lumen LED in the middle, and the Philips Hue LED on the right. The difference between the Lumen LED and the incandescent is fairly obvious -- but so is the difference between the Lumen LED and the Philips Hue LED, which carries an obvious purple glow. To be fair, the camera separates reddish hues from bluish ones more so than the naked eye does, meaning that in person, the Hue's light appears to be a more even, bluish shade of indigo. Still, we asked for blue, and indigo ain't blue.

So, what's going on here? Keep in mind that the Hue LED has only two blue diodes, and on their own, they aren't strong enough to put out a satisfyingly bright level of blue light. So, when you set your Philips Hue LED to blue, the bulb fires up those four red diodes, too. This gives the light a little extra oomph, but it also compromises the color accuracy. This isn't a problem for the Lumen LED, as its blue diodes clearly appear strong enough to give off bright, bold, accurate blue light.

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Those rather wimpy blue diodes in the Hue LED also come into play when you're trying to set the thing to green. With no pure green diodes, five dominant yellow diodes, and two weak blue diodes, you might expect an especially yellowy tone of green, and if you look at the graphs above, you'll see that's exactly what the Hue offers. This puts it at odds with the Lumen LED, which, like the green incandescent we tested, is able to produce a much more pure shade of green (I like to call it "Ninja Turtle green.")

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Colin West McDonald/CNET

You don't need chromaticity graphs to see the difference. Take a look at the three bulbs side by side, and it's easy to tell that the incandescent and the Lumen LED glow at a near perfect green, while the Hue LED gives off more of a tennis-ball tone. It's in the green spectrum, but only just barely -- and not anywhere close to that lovely shade of Ninja Turtle green that I'm so fond of.

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Philips Hue LEDs are terrific at accurately mimicking incandescent light of any color temperature. Colin West McDonald/CNET

Still, there's more to color-changing LEDs than the sorts of funky colors you'd use at a party. There's also a wide range of more natural tones, the kinds of color you commonly get from incandescents (plain, boring ones -- not the party bulbs we've been testing). Ideally, a good color-changing LED should be able to produce these tones, too.

This is where the Philips Hue LEDs really shine. In addition to a rainbow-like, full-spectrum color selector, the app offers a second color selector dedicated entirely to the types of tones produced by incandescents. If you want warm, yellowy light of around 2,700K, just slide over to the orange end of the spectrum. For hot, bluish-white light of around 6,000K, slide over to the blue end.

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When you plot the chromaticities of Philips Hue bulbs giving off natural, incandescent-style light, you'll find that they fall perfectly in line with the Planckian Locus. Wikipedia

With our spectrometer, we can test how accurate these tones are. If you were to take our chromaticity graph and plot out the different tones put out by incandescents of different color temperatures, you would get a line that curves up out of deep red through yellow, then back down towards blue. This curve is known as the Planckian Locus, and it's the target that any bulb trying to mimic incandescent light should aim for.

When we plot out the variety of natural tones that you can get out of the Philips Hue, we find that they always sit right along the Planckian Locus -- and that tells us that they're accurate. This wide array of accurate options for natural lighting is in stark contrast to what you'll get with the Lumen LED, which only offers one warm white, 2,700K tone as a default. Unlike the Philips Hue app, there's no color selector dedicated to natural tones. If you want an incandescent tone of a different color temperature than 2,700K, you'll have to find it within the full-color spectrum, a clunky and highly imprecise process that likely won't get you anywhere near that Planckian Locus.

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Colin West McDonald/CNET

The bottom line

With more vivid and accurate color quality, especially on the cool end of the spectrum, the Lumen LED would make an excellent light for a party, or for any other situation where striking colors are what's most important. Still, the Philips Hue does a respectable job overall, and it does a far superior one when it comes to reproducing the traditional tones of incandescent bulbs.

You won't want to purchase either one of these two options without first considering their comparative smarts, so be sure and check out our full reviews of each for the complete breakdown. We'll also be applying these tests and others to all new LED bulbs going forward (as well as a few we've already written about), so stay tuned for more in-depth lighting analysis.

About the author

Originally hailing from Troy, Ohio, Ry Crist is a text-based adventure connoisseur, a lover of terrible movies, and an enthusiastic yet mediocre cook. He has a strong appreciation for nifty, well-designed tech that saves time, looks stylish, and/or helps him avoid burning his dinner quite so often. Ry lives in Louisville, KY.

 

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