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Discussion Starter · #1 ·
Not wishing to bash other projection technology camps, but wishing to increase the information available (this is after all and information site, not just the CRT forum, or so I've been told). I would like to draw to your attention to this pdf . I will quote a section to give you a feel of what it involves:


"Flicker vertigo is an imbalance in brain-cell activity

caused by exposure to the low-frequency flickering

(or flashing) of a relatively bright light (such as

a rotating beacon; a strobe light; or sunlight seen

through a windmilling propeller). Flicker vertigo

can result in nausea, dizziness, headache, panic,

confusion, and in rare cases seizures and loss

of consciousness, which could result in a pilot’s loss

of control of an aircraft."


Having done a search for the word "flicker" in other Display Devices areas, it seems that lamp flicker can be a real problem. Unlike rainbows, it's not limited to DLP. Even CRT projectors can be forced to flicker, but increasing refresh rates makes it's more of a (nasty) novelty, and not a health risk.


You'd think mental health would be an important factor when choosing a display device, but then what would I know, I'm just a Luddite, clinging to outdated CRTs.



Cheers,


John


EDIT:You'd think mental health would be an important factor when designing a display device.......
 

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I suffer from this to a degree,one of the reasons I don't drive now is because of nearly crashing from the strobe effect of the sun shining through a vast row of trees as I was driving past,I nearly blacked out.

Same sort of thing with my computer monitor [was set to 50hz]when I looked even slightly away from dead center of the screen,my pereferal vision would pick up the flicker and make me feel sick.

It might be because of mastoiditis I had as a kid has made me more sensitive to flicker,a lot of people that I have run across with this same type of problem have told me that they have suffered from some sort of ear infection in the past.
 

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I must be lucky! I don't see flicker that much as 48Hz! I have not seen bulb flicker, but a DLP can give me a headache, but the is very high frequency flicker, not the low frequency variety.


Dave
 

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Discussion Starter · #4 ·
 Here 's a paper written in 1997 by a biomedical engineering student working with early DLP projectors, and theorising as to why she was sensitive to digital flicker.


" The light from a digital projector can be modeled as a temporal square wave because of its digital nature: either one or zero, on or off. The digital light projector (DLP) kit from Texas Instruments (TI) uses a 16-bit sub-sequence of full-on or full-off to yield grayscale. Analog monitors, in contrast, stimulate a phosphor that has a gaussian form for light emission in space and in time."


"The critical flicker frequency (CFF) is the highest frequency at which a particular person still sees flicker. At any higher frequency, the subject sees a steady light source. A study in Hungary in the early 1960s [2] found that five out of forty-two subjects (or almost 12%!) were unable to fuse a temporal square wave at 1100 cycles per second, the maximum rate available from their experimental equipment."



"I believe that flicker is a relatively minor but important problem at the moment. As the technology for digital projectors matures, flicker will be an important distinguishing characteristic because people are becoming more aware of health and ergonomic issues. Headaches and eye strain and reduced visual acuity caused by flicker will become an important issue. Despite this, I do not feel that flicker will directly affect this research project with DLPs at the moment or even in this decade. However, planning in advance, any technique to reduce square wave light output in favor of another wave form should be considered "better" than a pure square wave."



Cheer,


John
 

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I had theorized that it was about 10% of people that couldn't watch DLPs just from my experience. Interesting to see a study which found it was about 12% (albeit with a limit sample set).


Dave
 
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