Physique Question #9268
Mike fattori (Genre: mâle, Àge: 64 années) de Toronto sur 20 septembre 2015 demande:
When my smartphone is off, its screen is black. In the bright sun the black screen absorbs a lot of sunlight and gets very hot. If the phone was on - displaying a blank white screen - would the screen absorb less solar radiation because it's white?
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La réponse
Lorne Whitehead
répondu le 21 septembre 2015
Short answer: only a tiny bit less.
For an explanation first we asked Computing Science professor Brian Funt at Simon Fraser University. He's an expert on colour perception and computer algorithms for perceiving colours. He didn't know the exact answer but he speculated, "I would expect the answer is no because the white is emitted light, not reflected light. I assume the screen is the same [for both black and white] in terms of its reflectance properties. However, that’s just a guess."
Next we asked UBC Physics professor Jess Brewer. He said, "I'm just guessing, because I don't know if all smartphone screens are strictly based on backlit LCD displays. If they are, then I suspect the answer is a guarded YES, because a white LCD screen would still look white if the backlight were turned off, and therefore it must be more reflective."
Both scientists noted that having the screen on would use energy from the smartphone's battery and that would generate heat, but the questioner was only interested in the effect of sunlight.
In the end Lorne Whitehead, physics professor at UBC and expert on light reflection answered, "Jess is right, it makes a difference whether it is an OLED (Organic Light-Emitting Diode) screen, whose reflectance is independent of screen state, or an LCD (Liquid Crystal Display), for which there is a dependence. However, it's a tiny difference, because the color screens have very low transmission due to the RGB (Red, Green, Blue) color filter array. So overall, no matter what, the screen absorbs almost all of the ambient light that strikes it. By the way this is good for contrast, because otherwise the screen colors would be diluted by the reflected light. From the perspective of ambient light, a cell phone screen is very close to black.”
So basically there’s virtually no advantage to maintaining a white screen when your phone is in the sun.
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