They do look nice but there are gotchas. I have made a clock with them and 
here's some comments based on my experience:

If you multiplex them and retain incandescent lamps rather than converting 
them to LEDs then be prepared to replace the lamps quite often. That can be 
an expensive business if the displays use those little flange based lamps 
as mine do. In a multiplexed incandescent display to get the specified 
brightness you need to have a supply voltage of Vs * sqrt (N)  where Vs is 
the lamp rating and N is the number of digits. For 12V lamps and 6 digits 
that works out at about 30V which doesn't help the lifetime at all. You 
 also need a fail safe circuit in case the multiplexing stops.  I haven't 
any experience with direct drive and that may not be so hard on them.

It's hard to replace the lamps with LEDs and get equivalent brightness and 
colour. I've tried lots of different LEDs and have quite a collection of 
unsuitable ones to show for it. Part of the problem is the geometry of the 
LED light source compared to incandescents. Incandescents radiate in a 
spherical pattern from the filament and the displays fit them into little 
spherical wells designed to integrate the luminous flux into the plastic 
sheet. LEDs radiate in one direction and even the brightest ones don't 
manage to get the maximum light into the plastic so they look dimmer. The 
best LEDs for the purpose are the 5 mm diameter half height ones that allow 
a maximum amount of light to fill the spherical well. I save the blown 
incandescents and the LEDs fit into the bases quite nicely. I use the warm 
white ones to get a similar color to the originals but they are not as 
bright. 

They do turn up for sale from time to time but you will need to be patient. 

Good Luck,

Morris

On Saturday, 6 December 2014 11:45:34 UTC+11, westdave wrote:
>
> Dear Mr. Santa ,this year i would like some light pipe displays , 
>
>  

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