[time-nuts] Hi Power LED Light power supply...

[Hal Murray]

lists at rtty.us said:
> There are a *lot* of TV's out there that refresh at 60 Hz or less. 

Many years ago, we had a busted fluorescent light at work.  I could see the 
flicker out of the corner of my eye.  I found it annoying, so I'm a firm 
believer that some people can see flicker in some conditions.  (Fortunately, 
it was in a location where I didn't spend much time.)

Direct vision was not a problem.  I assumed the lamp was running at 60 Hz 
rather than 120 and that peripheral vision was better at detecting 
flicker/motion.


Wiki has an interesting page on this stuff:
  http://en.wikipedia.org/wiki/Flicker_fusion_threshold

the rod cells of the human eye have a faster response time than the cone 
cells, so flicker can be sensed in peripheral vision at higher frequencies 
than in foveal vision

But also:
The maximum fusion frequency for rod-mediated vision reaches a plateau at 
about 15 Hz, whereas cones reach a plateau, observable only at very high 
illumination intensities, of about 60 Hz
(I think that is backwards from the previous line.  I'd guess somebody typoed 
rods-cones.)

Note that LEDs without diffusion are high-illumination, so I'm not surprised 
if some people report flicker troubles.  It would be interesting to 
investigate some examples.  I wonder if they are 120 Hz or 60 Hz?


More wiki:

For the purposes of presenting moving images, the human flicker fusion 
threshold is usually taken as 16 hertz (Hz). In actual practice, movies are 
recorded at 24 frames per second, and TV cameras operate at 25 or 30 frames 
per second, depending on the TV system used.

Even though motion may seem to be continuous at 25 or 30 frame/s, the 
brightness may still seem to flicker objectionably. By showing each frame 
twice in cinema projection (48 Hz), and using interlace in television (50 or 
60 Hz), a reasonable margin of error for unusual viewing conditions is 
achieved in minimising subjective flicker effects.

 
  

-- 
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