I'm a student, very new to this, and need help. Want to build my first scanner.

[White-Light]

Hi,


Also you mentioned combining R, G & B lasers to make white. There is a useful doc on Laser f/x that describes that because our eyes perceive different colour light at differing non-linear intensity, you need an almost golden ratio of Red to Green to Blue in the proportion 4.6:1, 1:1 & 2.6:1 to achieve white. The page in question is http://www.laserfx.com/Backstage.Las...Archives4.html .


Simon B.

Hi Simon,

I would suggest that Doc was probably written some time ago.

White balance ratios depend on the wavelengths of the lasers used as differing wavelengths have differing brightnesses and colour shades and thus effects on the colour mix. Those ratios look very much as though they were written for 660nm or even 670nm red (I forget the ratios for the higher wavelengths these days) and 473nm blue.

For modern choices of 638 or 640nm red and 445nm blue, the accepted ratio these days is 1:1:1 for a good white balance.

For other wavelength combinations eg. 650nm red, you'll need to research the ratios.

Sent from my laptop.

[simonb]

Thanks for this info. I had read it somewhere, but cannot find it.

Yes, the doc describing the differing ratios seems to have been written with Helium Neon lasers in mind (632.8nm) and probably Argon also. Definitely not more modern wavelengths.

The following link attempts to explain why:

www.dreamlasers.com/support/tech-laser-app. .

There is a missing page to this that shows mathematically how to compare the apparent brightness of light at different wavelengths. I believe may be a reason why bright green 532nm D.P.S.S lasers have in the past been described as appearing 3 to 4 times brighter than similar coloured Argon laser beams. A hologram making friend of mine insists his green laser module is much brighter than the argon he used to use, & that exposure times are shorter too.

I'm not claiming that is the case, but it is a fact that the human eye has a noticable non-linear sensitivity to colour, whilst fully realising the reasons & implications of this. This is definitely a qualitive rather than a quantitive thing.

So would if you mixed equal power (say 1W) Red, Green & Blue lasers using dichroic filters you would obtain a reasonable white light? (assuming typical modern wavelengths of 640, 532 & 445nm for RGB & B respectively)? If so, why does the above non-linear characteristic not affect this?

I know this is arguing a point, but I really want to know the reasons why this is the case.

Many thanks,

Simon B.

I can paste the equations here if anyone is interested in say comparing the apparent brightness of a modern 445nm blue laser to the classic 488nm blue argon, or the 632nm red Heliun-Neon.

Hi Simon,

I would suggest that Doc was probably written some time ago.

White balance ratios depend on the wavelengths of the lasers used as differing wavelengths have differing brightnesses and colour shades and thus effects on the colour mix. Those ratios look very much as though they were written for 660nm or even 670nm red (I forget the ratios for the higher wavelengths these days) and 473nm blue.

For modern choices of 638 or 640nm red and 445nm blue, the accepted ratio these days is 1:1:1 for a good white balance.

For other wavelength combinations eg. 650nm red, you'll need to research the ratios.

Sent from my laptop.

[simonb]

I'm still a bit unsure about this matter of equal amounts of green & blue.

White-light has said above that you don't need much more blue than green, & that equal 1W lasers are ok, but earlier in this thread (22 May) Bradfo69 confirms what I thought, that you need 5 times more blue than green (4.6:1 actually!). With the red at 2.6:1.

See http://www.laserfx.com/Backstage.Las...Archives4.html for details.

Are there any other ideas or reasons concerning this?

Thanks again,

Simon B.

[james]

Take a look at this:

http://en.wikipedia.org/wiki/Color_vision

This is most interesting:

http://en.wikipedia.org/wiki/File:Eyesensitivity.png

As you can see, green is the most easily seen color by far.