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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Notebooks > MBP Sleep light flickering

MBP Sleep light flickering
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Join Date: Jun 2006
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Jul 11, 2006, 05:54 PM
No this is not another complaint about some MBP feature malfunction but is an observation of one of its features. I'm sure everyone would know by now that their MBP's sleep indicator light changes brightness to simulate a breathing rythm. Isn't that rythm obvious when one is sleeping Well, I discovered that the rythm is a bunch of different brightness levels changing at high speed and can be caught with a cheap digicam. Check out the crappy video here. Enjoy
Join Date: Oct 2001
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Jul 11, 2006, 08:18 PM
This is the way the sleep LED has worked since the Titanium Powerbooks. The technical reason is because the light is controlled by a PWM (pulse width modulated) signal, the same type of signalling as is used to control the LCD panel backlight brightness. So when the light is at its brightest, the brightness occurs because the LED is "more on" than it is off. When the light is at a reduced brightness, it is "more off" than on. With the slower frame rate of the camera, you are seeing some of the pulses within the PWM signals. The light cycling between on and off saves power and works well with an LED that naturally is only on or off. Wikipedia explains it rather well:


marsbt  (op)
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Jul 11, 2006, 09:02 PM
Nice pointer steve. Although I did know about the PWM signals, but didn't know that MBP light also used the same principal. Thanks.
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