Re: [MF 3D] MF viewer lighting

[Richard Rylander <rlrylander@xxxxxxx>]

Greg Erker wrote:

>
>   So has anyone else played with the
> cold cathod fluorescent tubes we discussed
> about a month ago (available from
> DigiKey). Any colour comparisons to
> white LEDs or 5000Kelvin light panels.
>

Hewlett Packard has recently introduced white LEDs with
color-temperature grading:  http://www.hp.com/pressrel/mar99/15mar99.htm

These lamps have a color temperature of 6500K and a Color Rendering
Index (CRI) of 75 (i.e., a reasonably continuous spectrum).

LEDs are pretty close to ideal light sources - very bright, long-lived,
energy efficient.  If it weren't for that #%&! collimating lens that
restricts angle of view (enhancing apparent brightness)!  A modification
I've made to LEDs used in backlights is to cut off the lens (using a
Dremel emery cutting wheel - and being careful not to nick the embedded
thin wire connecting the chip to one of the leads).  The cut surface is
then sanded with #400 wetted sandpaper (very little sanding is needed as
the Dremel wheel makes a smooth cut) and polished  with "Blue Magic"
polishing compound (available from Micro-Mark).

These modified LEDs have a very wide illumination pattern.  Mount them
in a reflective chamber with a decent diffuser and voila - instant
backlight.  I've made a twin 35mm viewer this way, using 4 LEDs per side
for increased brightness and uniformity of illumination.

Richard Rylander