[Gllug] Two Questions

[Andrew Farnsworth]

Chris Bell wrote:

>On Wed 09 Feb, Nix wrote:
>  
>
>>On Wed, 9 Feb 2005, David Damerell prattled cheerily:
>>    
>>
>>>OTOH the two are not directly comparable; 60Hz will boil your eyeballs
>>>on a CRT,
>>>      
>>>
>>Will it? It's fine here, as is 78Hz and 92Hz.
>>
>>50Hz under fluorescent or incandescent light, on the other hand, is
>>insane. :)
>>
>>    
>>
>
>   The combination of eye and brain appear to naturally work at the sort of
>frequencies known to give flicker effects, but the early cine film workers
>soon discovered that doubling the frequency by flashing the light twice for
>each frame removed most of the annoying effects.
>   There are different screen phosphor persistences available for different
>purposes. Broadcast TV runs on a 50Hz field interlace, 25Hz full picture,
>rate so standard TV's are usually supplied with a medium persistence
>phosphor screen. Computer monitors are generally sold by size rather than
>quality, so who cares about things like gamma, colour integrity, and
>phosphor persistence as long as it is cheap? Who bothers to fit expensive
>long persistence colour matching room lighting?
>  
>
The other issue is that the florescent lights run at 50hz too so between 
the screen and the lights running at 50hz you get a heavy flicker affect 
on a CRT monitor.  With LCD you don't have this problem.  Note that in 
the US the AC frequency is 60hz which also makes it worse.  That is why 
most people set the refresh to 72 hz or higher.  Interestingly enough 
the 1/60 of a second is the speed that a camera shutter is set to so 
that it synchronizes with the flash which is why when you take a picture 
of a TV or monitor you get strange banding in the picture.  The 
Macintosh used to have a tool that would fix this problem, one of the 
many reasons that the Macintosh was used in to many movies, this tool 
basically set the monitor refresh rate to 60 hz.

Amazing the trivia you pick up over the years.

Andrew Farnsworth
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