[lightarrow (OP)]

Which is a typical value of illuminance (lux = lumen/m²) of a photocopier on a sheet of paper to copy?

[lyner]

I ran my Epson scanner with my Weston Master V exposure meter right over it.
The maximum reading I could get registered an EV of just over 12
That, according to wiki, represents 10.24lx.
Any use?
I could find nothing on the web'
I think a commercial copier is quite a bit brighter than that - they scan five to ten times quicker, I'm sure, so the illumination will need to be greater, pro-rata, for the same signal to noise ratio.
So, should we say >50lx ? They are offensively bright.
Why do you ask?

[lightarrow (OP)]

That's very low, I thought it would be greater.

According to wiki, a standard level of illuminance for an office is 500 lux, and full daylight more than 10,000 lux:
http://en.wikipedia.org/wiki/Lux

I thought a photocopier illuminance was sensibly greater than that of a normally illuminated room and the idea was to prevent not-allowed photocopying of books making the ink someway light-sensitive (clearing at very high levels of illuminance).
So, my idea has miserably faild... []

You know, photocopying of books is a big problem, especially for scientific books; I went to the biggest bookshop in Florence, some days ago, scientific books are almost totally disappeared. Some years ago there were more than two entire rooms full of scientific books, now only a couple of shelfs. Terrible! Where will scientific knowledge go? Towards non-controlled, arbitrary internet informations?

[LeeE]

I think that for Xerographic reproduction the luminance might be higher, but more important I think, will be the wavelength.  A scanner won't give the same light as a Xerographic copier because all the light in a scanner needs to do is provide enough illumination for the target to be optically scanned; in a Xerographic copier, the light needs to neutralise the charge on the receptor drum.

Modern copiers tend to be scanner/laser printer combos, rather than use the older Xerographic technique; they're cheaper, as they can use commodity scanning/printing hardware, and can allow out-of-order job processing and image correction & enhancement.

[lyner]

You must be right. Lee - for old Xerox types.
It must have been very hard to get colour rendition using the old method - even more light / slower scanning, I suppose.

[techmind]

It can be fairly high brightness, but for quite a short time. On copiers with a scanning light source, my gut feeling is that it'll never be significantly brighter than full-sunlight - and often will be much less.

I did used to know an old high-speed photocopier which must have used the direct Xerographic technique with a flashgun which illuminated the whole page at once. Haven't seen one of those for more than a decade though.


Colour copiers especially have digital image- and pattern-detection software built in which may stop you copying banknotes, certificates, official documents etc. On some copiers the 'Eurion' constellation triggers this, but for others one suspects it's a more generic fine-swirly-line type algorithm.

See also:
http://en.wikipedia.org/wiki/EURion_constellation
http://www.cl.cam.ac.uk/~mgk25/eurion.pdf
http://www.sscnet.ucla.edu/geog/gessler/collections/steg-eurion-constellation.htm