[Trac #733] Status LED's take enough power to matter.

[Zarro Boogs per Child]

#733: Status LED's take enough power to matter.
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 Reporter:  jg        |        Owner:  mlj    
     Type:  defect    |       Status:  new    
 Priority:  high      |    Milestone:  BTest-3
Component:  hardware  |   Resolution:         
 Keywords:  relnote   |  
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Comment (by rsmith):

 Replying to [comment:4 jg]:
 > We're going to take a close look at power consumption and use of the
 LED's; it is way too high for ebook mode.
 >
 > Richard, what is PWM mode?

 Tom responded to Jim via IRC but I'll cover it here for anyone else who
 doesn't know.  PWM stands for pulse width modulation.  Its a method of
 driving devices such that you don't leave them "on" the entire time.  An
 example would be to drive a LED at 60hz with 50% duty cycle so for half of
 the 1/60 of a second the led is on and for the 2nd half its off.  You are
 still flashing the LED at 60 Hz which is faster than the human eye can
 detect but since its off for half the time you save power during that
 period.

 Gory details can be found here http://en.wikipedia.org/wiki/Pulse-
 width_modulation

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Ticket URL: <http://dev.laptop.org/ticket/733#comment:5>
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