# mobile devices - screens light up when charge cords plugged in **URL:** \ **Category:** Factual Questions\ **Created:** [May 23, 2013, 3:31am UTC](https://boards.straightdope.com/t/mobile-devices-screens-light-up-when-charge-cords-plugged-in/659089 "2013-05-23T03:31:52Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [May 24, 2013, 9:17pm UTC](https://boards.straightdope.com/t/mobile-devices-screens-light-up-when-charge-cords-plugged-in/659089/22 "2013-05-24T21:17:17Z")
> [@jz78817](#): > > IME when a CCFL backlight fails it’s usually the inverter and not the tubes themselves. As for backlight LEDs, I’m sure **Michael63129** will correct me if I’m wrong but I don’t think they qualify as “high power” in this context. At least, they’re not run as hard as the diodes used in things like LED light bulbs (where much of the “bulb’s” mass is heatsink.) > > as far as OLED, AIUI the limiting facter is still the blue element. Supposedly the red and green have reasonably long lifetimes, but blue “wears out” (grows dimmer) at a substantially faster rate. Digi-Key has a good article explaining LED lifetime [here](http://www.digikey.com/us/en/techzone/lighting/resources/articles/determining-led-rated-life.html), with graphs showing how operating conditions affect lifetime; for example, they show a 1% decrease in brightness over 7,000 hours at 25°C, but a much larger 11.5% decrease at 85°C, a typical operating temperature in an LED replacement bulb; the LEDs used in cell phone backlights are just your standard low power type LEDs (e.g. 20 mA, 50-100 mW power). Even for high-power LEDs, I suspect that the vast majority of lamp failures will be due to the ballast electronics, plus even if the LEDs in a cell phone lasted for only 50,000 hours, that would vastly exceed the lifetime of the phone itself. Also, OLEDs are based on a different technology (organic polymer, basically plastic) than traditional semiconductor-based LEDs (which are also used in displays, as in large electronic billboards, but presumably too expensive or difficult to use in miniaturized displays). ---
**Author:** ![Oly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/oly/32/8255_2.png) [@Oly](https://boards.straightdope.com/u/Oly)\ **Post date:** [May 25, 2013, 12:26am UTC](https://boards.straightdope.com/t/mobile-devices-screens-light-up-when-charge-cords-plugged-in/659089/23 "2013-05-25T00:26:51Z")
> [@Rick](#): > > Well it took some time but I tracked down the person responsible for the screen illuminating for 8 seconds at Apple. > A very nice young lady named Locks. I asked why 8 seconds? Here is her response > If you have any further question refer them to Goldie. Ms Locks was obviously swayed by the younger member(s) of the focus group. ---
**Author:** ![guizot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guizot/32/3636_2.png) [@guizot](https://boards.straightdope.com/u/guizot)\ **Post date:** [May 25, 2013, 8:04am UTC](https://boards.straightdope.com/t/mobile-devices-screens-light-up-when-charge-cords-plugged-in/659089/24 "2013-05-25T08:04:00Z")
> [@jz78817](#): > > lolwut > > you’re not cramming 120VAC into your phone :rolleyes: a generic micro USB charger delivers up to 0.5 amps at 5 volts DC (i.e. one watt) to the device, same as a standards-compliant USB port on your PC. any power used to light the display is deducted from that one watt and is not used to recharge the battery. Of course you’re not cramming 120v into the phone–that’s not what I’m saying. My point is just that in theory there’s enough power from the outlet to both charge the phone at maximum rate and light the display at the same time, if the phone is designed to take advantage of a charger with more than one watt. Granted, it’s not likely to be doing that, but it’s possible. [Previous page](https://boards.straightdope.com/t/mobile-devices-screens-light-up-when-charge-cords-plugged-in/659089.md?page=1)