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CRT Strobe Effect

03/04/2008 11:26 AM

Could someone explain to me what creates the "strobish effect" when you wave your hand at a CRT computer screen? It doesn't happen for LCD monitors or regular televisions.

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Commentator

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#1

Re: CRT Strobe Effect

03/04/2008 3:05 PM

60 hz. cycle flicker! The CRT screen go's on and off everytime the AC sine wave passes zero or 120 times a second. Hence the strobe effect. LCD's aren't affected by 60 cycle flicker.

Taa-Da!

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#2

Re: CRT Strobe Effect

03/04/2008 3:06 PM

This effect is most noticeable with an oscilloscope screen, which is a one line TV screen basically....

If you are chewing on a biscuit or something crunchy the vibrations in your head cause the eyes to deviate from the position the brain is pointing them at, and so the line on a 'scope screen will seem to have an odd waveform on it!!!

Which of course nobody else can see... I think this must be a similar effect to your waving your hand in front of the screen. As the screen is updated only every so often the strobing you get by moving you fingers in front of the picture depends on the speed of response of the phosphers of the CRT or the switching time of the LCD pixels...

Check your monitor settings I bet you're using a slow refresh rate on your monitor!!

John.

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#3

Re: CRT Strobe Effect

03/04/2008 3:07 PM

Forgot TV scanning electron gun minimizes the flicker.

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#4

Re: CRT Strobe Effect

03/04/2008 4:42 PM

It does work for LCD (and regular TVs) .. if I wave my paw in front it looks like I have about 8 claws

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#6
In reply to #4

Re: CRT Strobe Effect

03/05/2008 3:21 PM

Ummm, not to get too personal, but how many claws is it supposed to look like you have?

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#5

Re: CRT Strobe Effect

03/05/2008 1:34 AM

If you want to see something neat, get a thin string of elastic, hold it up in front of your TV, and pluck the string. As you pull on the ends of the elastic the frequency of vibration will change. When it's near the scanning rate of the TV picture tube, you will see the wave on the elastic string stand still!

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#7
In reply to #5

Re: CRT Strobe Effect

03/05/2008 3:23 PM

Obviously this will work better if you have three or more hands...

Didn't we already have this discussion, about four-handed aliens?

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#8
In reply to #7

Re: CRT Strobe Effect

03/06/2008 12:52 AM

That's what God gave you a tongue for.

And now, the three-handed banjo!

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#9

Re: CRT Strobe Effect

03/06/2008 10:39 AM

Hi Paddy,

Some of the likely causes include:

1) Bad CRT power supply

2) CRT itself is going bad

3) Incoming power frequency is not stable at 50/60hz.

I would check the power supply first.

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