RE: filmscanners: LED Illumination for Film Scanners

[derek_c@cix.co.uk (Derek Clarke)]

darkroom@ix.netcom.com (Austin Franklin) wrote:

> > > > An LED light source for enlargers was not done 15-20 years ago
> > > > because it
> > > > was not possible. Blue LED's did not exist as anything other than
> > > > laboratory
> > > > curiosities until within the last 5 years.
> > >
> > > Sure you could have done that 15-20 years ago.  Use filters...red,
> > > green and
> > > blue filters certainly were around 15-20 years ago.
> >
> > LEDs are monochromatic light sources and can't be filtered to another
> > colour.
> 
> If blue LEDs were not available, outside the lab, as stated above, 
> until 5
> years ago, they why were there blue lenses available for LEDS in at 
> least
> the early 90's if they did nothing?
> 
> 

My guess would be that perhaps a conventional red LED (not a laser LED, 
which by definition is strictly monochromatic) has a wider spectral 
response than I gave it credit for.

You wouldn't be able to get much light by filtering something that is 
mainly red though.

The blue LEDs recently developed have most of their output in the blue 
part of the spectrum, and are rather better suited for turning into blue 
laser diodes.

I know laser diodes aren't used in film scanners, but the driving force in 
LED development is for lasers in shorter and shorter wavelengths to allow 
optical storage of higher and higher capacity.