Panaplex display history

[Chuck Guzis]

On 05/30/2015 10:40 AM, tony duell wrote:

> Is there a good reason why filament lamps were used on minicomputer
> front panels until the mid 1970s? Things like the PDP11/45, Philips P850, etc
> all used filament bulbs, not LEDs.

I can think of a few reasons.

First, a filament bulb has the effect of visibly "stretching" a visible 
pulse.

Second, a filament lamp in an indicator application with a "keep warm" 
provision can have an extremely long lifetime.  Nobody knew what to 
expect as the lifetime of a GaAsP device.

Third, I'm not entirely certain what the supply situation was in, say, 
1974. Incandescent lamps were plentiful and available and inexpensive. 
  But new equipment certainly had LEDs as indicators in 1973.

Fourth, inertia.  Consider how long it's taken for the automotive 
industry to adapt to LEDs for even the simplest indicator applications. 
  Telcos were similarly slow on the adoption of LED technology.

The reliability problem was real--I still have some 7-segment displays 
from the mid-70s that have non-working LED segments.

--Chuck