[Novalug] OT: monitor distance

[Dan Arico]

On Friday 09 November 2007 09:37, Nino Pereira wrote:
> Justin,
>
> this question is not rhetorical at all, since in fact I do have
> access to such equipment. However, I have never thought to try
> it out on the X-rays coming from my monitors.
>
> The reason is simple: you don't expect any. As you know, the
> CTR is a vacuum tube whose electrons are steered in the right
> direction to make phosphors light up in the right pattern of
> pixels. I don't know for a fact how energetic these electrons are,
> but I believe they are below 25,000 Volts. In the X-ray business
> this energy is considered low (your chest X-rays are made by 75,000 V
> electrons), and the resulting X-rays don't go very far: they get stuck
> in the monitor's glass, which is quite thick (so that CRTs are heavy).
> Moreover, the electron current is low, at most a milli-amp (otherwise,
> you'd need more power to run the CTR and the screen would get warm).
>
> On the tube's sides and back there may be less material in the tube
> itself, but there's other material (the case, etc.), so that X-rays
> can't escape there either.
>
> Although I don't expect to see anything, it would be nice to
> confirm my suspicion that there's no problem with X-rays from CRTs.
>
> Nino

I have seen one occasion in the past where a CRT started emitting X-rays.

With age, the phosphors dim. Usually something else goes before this becomes a 
problem, but I ran across one monitor that had been "repaired" by jacking up 
the voltage to brighten the image.

Dan

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