This is one of the nerdier posts I've done, but since I'm unabashedly a nerd, and I hope many of you are too, I figured it would work. You see, I love LEDs. I think they're fascinating in how they work, what they can do, and so on. As you'd expect, I'm slowly replacing the CFL bulbs in my house with LEDs. The thing is, not all LED bulbs are equal, and one of the biggest drawbacks is that not all offer the "warmth" in color temperature most of us love in incandescents. So I put a few different LEDs on my test bench, measuring them sort of how I measure TVs, to see how they do. Curious? Well I was, hopefully you will be too. First, my methodology. In theory, the way to measure an LED or CFL bulb is to measure it directly. As in, aim the meter right at the bulb. Since the Photo Research PR-650 I use is my PR-650 (not S+V's) I didn't want to throw that many photons at it. It would probably have been fine, but like staring at the sun, it's not something I want to do every day. So instead, I measured what the bulbs produced as reflected off a white reference. This certainly wouldn't give us perfect numbers, but within the logic of this article, the numbers would at least be roughly comparable. I waited for the bulb's color temp to stabilize before I measured it. In addition to color temp I measured all the bulbs' light spectra using CalMan. The Philips Hue, for instance, obviously creates "white" in a far different way than an inexpensive "regular" LED bulb. Amazingly, long forgotten in the bottom of a box appropriately labeled "Light Bulbs," I found an ancient, but still in its package, incandescent. Let's start with that. (Oh, and these are in anti-clockwise order in the image at the top) Philips Appliance "Frost" (25 Watt, incandescent) Color Temp: 2488K As you can see, even though the bulb was labeled "Frost," it's got a very warm color temperature. To my eyes (and mental well-being), I prefer warm light. This, I think, is a cultural thing. In other countries I've visited, they prefer a much cooler (bluer) light. The spectrum isn't surprising either, given it's just a filament heated with electricity. Philips "Twister" (9W, compact fluorescent) Color Temp: 2750 kelvin This is a small CFL, and produces a claimed "2700K." Most new bulbs list a rough color temperature, beyond the "Soft White" or "Bright White" labels. Seems pretty spot on. The spectrum sure is interesting, isn't it? What is "white" anyway? I also measured a 23W version of this lamp, and it measured 2704K. GE "Helical" (10W, compact fluorescent) Color Temp: 2777K More of the same here. The spectrum looked the same as well. Bright Effects "L13T6" (13W, compact fluorescent) Color Temp: 2763K The house brand for Lowes. This one was labeled "27K." Maybe they meant "2.7kK." I tested a higher wattage version, and it too measured the same. Seems like after enough years of development, these bulbs are spot on what they claim to be. One oddball, then on to the LEDs. Feit Electric "BPESL 13T/R" (13W, compact fluorescent) Color Temp: N/A This is a party CFL. Can you guess what color? I was just curious what the spectrum would look like. Philips LED A19 (8W, LED) Color Temp: 2666K These are $20 each at Home Depot. A19 is the size, but there's no other "name." These were one of (if not the) first mass market LED bulbs. They're labeled 2700K, and they nail that. The "yellow plastic" covering is actually why the spectrum looks the way it does. There's no such thing as a "white" LED. Instead, to create a white light, a blue LED is used (notice the spike in the blue part of the spectrum), and a yellow phosphor is used to fill in the rest (the big hump). Subjectively, even though the color temp is the same, the quality of the light is different. It's more... natural or something. It's hard to describe, but even though the CFL and the LED are both the same shade of "white," there's something about the CFL that just looks like artificial lighting, while the LED just looks more like "light." Beyond the energy savings, I think I'm going to accelerate my replacement of CFLs just because the LEDs look better. That's not something I really noticed until I did these back to back. I also measured the top-firing version, and it was identical (save its dispersion pattern, obviously) If only they were cheaper. Oh wait... Cree A19 (6W, LED) Color Temp: 2764K These are brand new, and only $10 each at Home Depot (less in bulk). They're not quite as warm as the Philips, but they're really close and half the price. I've bought a bunch. These are also labeled 2700K. I measured the 9.5W version and it was nearly identical. Philips Hue (8.5W, LED) Color Temp: 2748 I reviewed the Hue a few months ago. It's a cool idea: programmable LED bulbs, with an smartphone/tablet app to control them. The reality somewhat misses the mark. The bulbs, though, are fantastic. In their "base" state, as in what they do if you just turn them on, is a lovely warm glow. But as you can see from the spectrum, how they create "white" is very different than the other LED bulbs. Because the Hue has to be able to create all the colors of the rainbow, there are (presumably) red, green, and blue LEDs inside the translucent casing. The internal processor has a preset that says X amount of red, green, and blue are needed to create 2700K. Since there aren't three distinct peaks, there's probably something additional going on. Orange Tree Trade Soft White LED Rope Light (multiple LED) Color Temp: 2870 They claim "2800K to 3000K." Honestly, it seems cooler than 2870. A difference of 150K compared to the others here doesn't (and shouldn't be) a big difference, and maybe it's just my eye, but I was all ready to complain about how blue these are and... well not so much I guess. The same with the next one. SuperBrightLED.com "G9-xW24" (N/AW, LED) Color Temp: 2815K I bought some cool hanging track lighting that came with halogen bulbs. Halogens are about as efficient as running an air conditioner backwards to cool the yard. No way. There were very few options available for the small G9 connector. SuperBrightLEDs.com sold this model, listed as "Warm White" 2900-3200K. These look cooler than the numbers suggest too. Compared to the Philips LED, these and the Rope Lights are definitely cooler, but compared to the other bulbs here, they're in the ballpark. If you were to put these and the Philips side by side, you'd undoubtedly see a difference. Though I didn't have any on hand to measure, "white" Christmas lights are often very cool in color temp. Whether this is by design or by necessity remains to be seen. The phosphor in "white" LEDs adds to the cost, generally speaking cheap "white" LEDs are going to be cooler/bluer in color temperature. This goes for any time of "white" LED. Bottom Line Turns out, the color temp rating on light bulbs is a lot more accurate than the numbers supplied by any TV company about their products. I figured this was certainly worth checking, though, and maybe it's just me, but I found the different spectra, and how each creates "white," to be really interesting. I guess I'll end with a word of caution. There's enough variation between the different companies, even if it's only 100-150 kelvin, that if you want a uniform color temperature for the lighting in your home, you're probably better off sticking with one brand, and ideally, the same batch and bulb size.