Re: filmscanners: LED Illumination for Film Scanners

[Jim Snyder]

on 6/21/01 8:00 AM, rafeb at [EMAIL PROTECTED] wrote:

> At 11:18 PM 6/20/01 -0400, Isaac Crawford wrote:
> 
>> Well halogen bulbs have the same uneveness problems as regular bulbs,
>> but with the use of a mixing chamber, they can give the same results a
>> "cold" head can... I can see some potential advantages in an enlarger
>> with LEDs in this arangement, primarly concerning heat. I'm not sure
>> what sort of advantage LEDs would have in a scanner, maybe long life
>> with minimal shift (light wise)?
> 
> 
> The *problem* I see with cold-cathode and fluorescents is that
> they can flicker.  I'm not exactly sure why this happens.  Is
> it a power-supply problem, or is it a property of the bulb, or
> a combination of the two?

It is a property of the bulb. It is using 60 Hz pulses of AC to excite
phosporescent matter, so one pulse may not excite as much as the previous or
following pulse, and we see at 60 Hz...

Jim Snyder