Re: filmscanners: LED Illumination for Film Scanners

[Arthur Entlich <artistic@ampsc.com>]

If I'm not mistaken, all A.C powered fluorescent bulbs "flicker" at 
60/50 cycle (in those places that use 60 or 50 cycle AC, that is).  In 
fact so do incandescent bulbs, for that matter, but in both cases, 
aspects of the design reduce the visibility of this.  I think television 
screens also do so at some frequency..., and we know that computer 
monitors do, and the higher the frequency the less obvious, at least on 
a conscious level.

In the case of fluorescents (and televisions and CRTs), the phosphors 
have a long enough lag activation period to "bridge" this rather short 
fraction of a second.  In the case of incandescents, the filament 
remains hot enough to bridge that difference in electrical flow.

I plead total ignorance in how DC powered bulbs fare, however.

Regarding the Leaf scanners.  I knew they were off my want list when I 
saw the bulb for one being sold on ebay, as a separate auction item ;-)

Art

Austin Franklin wrote:

>> The *problem* I see with cold-cathode and fluorescents is that
>> they can flicker.  I'm not exactly sure why this happens.
> 
> 
> Typically it is caused by the observer being on some psycho conducive
> substance ;-)
> 
> The Leaf uses a "tri-band phosphor fluorescent lamp", which I would guess
> doesn't have the fluctuation problem you mention, or if it does, it does not
> seem to matter.