This year’s “Flame Challenge” is to explain color in terms an 11-year-old can follow. I have opinions on this subject, a background in AMO physics, and access to scientific equipment, so I’m putting something together. In the course of this, though, it occurred to me to wonder how my different portable computing devices process color. And since I have access to an Ocean Optics USB4000 spectrometer, I can answer this question in more detail than anybody needs.
So, I have three principal electronic devices that I use to do computer-type things: a Moto X smartphone, an iPad, and a Lenovo ThinkPad laptop. So, I had all three display a flat white screen, put the spectrometer probe up against the screen, and generated the following graph:
All three of these show three principal peaks, corresponding to the red, green, and blue pixels making up the display. You can see that the iPad and laptop are pretty similar, but the phone is strikingly different. If you isolate the red component from each, you can see the difference more clearly:
(These are normalized, making the peak intensity the same for all three.) The iPad and laptop have a little bump out in the blue, which isn’t there on the phone. The red light from the phone is also a little narrower, more symmetric, and slightly longer wavelength at the peak.
But the difference is most pronounced with the blue component:
Again, the phone is a bit narrower and slightly longer wavelength, but the most striking difference is that the iPad and laptop both have double-peaked distributions, with a substantial amount of green light in the blue display.
I was kind of surprised to see this, though I’m not sure exactly why, given that I don’t know what the light sources are for the different devices. A bit of Googling suggests that this is because the Moto X uses an organic LED display, which is directly producing light in three specific bands, while the iPad 2 uses a backlit display with a broadband source and color filters to get the red, green, and blue. This blog post is talking up a different technology, but includes a nice graph of the basic filter situation. The laptop is a Lenovo Thinkpad X220 and of similar vintage to the iPad, so probably similar display technology.
Probably the most striking thing about this, though, is how little difference it makes. That is, if I put the phone right next to the laptop with both showing blue, I can see a difference between them, but despite the dramatic difference in spectra, the difference in appearance is really, really subtle. Which just goes to show you the kludgey nature of the way our eyes process color. Which is a good deal of the point I want to make for the whole “Flame Challenge” thing, which is why I was looking at my laptop with a spectrometer in the first place…