With apologies for one further mail on this topic... Steve is right, and I 
stand corrected.

As far as I can determine, the light sensor on a MacBook Air (well, mine, at 
least) is about 1-4mm to the left of the webcam aperture in the screen 
surround. 

This means that you can block the webcam without interfering with the automatic 
screen brightness function - but you need to position your webcam-blocker as 
carefully as in Steve's picture, and from the right of the lens aperture.

Serves me right for (a) making assumptions and (b) using my left thumb to 
occlude the lens. If I had used my right thumb, I wouldn't have made the same 
assumption (!)

Thanks Steve!

Robin 
 
On 28 Feb 2014, at 16:52, Robin Wilton wrote:

> Apologies - I should have been more specific... my Macbook Air doesn't have a 
> separate light sensor... it's in the same orifice as the camera lens.
> 
> R
> 
> Robin Wilton
> Technical Outreach Director - Identity and Privacy
> Internet Society
> 
> email: [email protected]
> Phone: +44 705 005 2931
> Twitter: @futureidentity
> 
> On 28 Feb 2014, at 14:54, Steven M. Bellovin wrote:
> 
>> 
>> On Feb 28, 2014, at 2:41 PM, Suhas Nandakumar <[email protected]> wrote:
>> 
>>> 
>>> (incidentally, if you're using a Mac and you cover the webcam lens, you'll 
>>> need to turn off the automatic screen-dimming function. System Preferences 
>>> -> Displays )
>>> 
>> 
>> Not really -- the light sensor on many Macbooks, at least, is to the left of 
>> the camera lens.  This just came up on Twitter; here's my set-up at 
>> https://twitter.com/SteveBellovin/status/439412122410184704.  (I don't want 
>> to clog the list with a large picture attachment.)  Yes, it works, and if 
>> you find me here I'll show you what happens if I move the slide to the left 
>> a bit more.
>> 
>> 
>>              --Steve Bellovin, https://www.cs.columbia.edu/~smb
>> 
>> 
>> 
>> 
>> 
> 

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