> How much LEDs (of the average, 5mm/20mA kind) must I roughly
> use to make a 7-segment display that has good visibility in
> 'average' outdoor daylight? The application is a countdown display
> for a car race, each digit 20 .. 50 cm high. Any experience, URLs?

Hi, I got asked to look at something similar a couple of years
ago and in the end rejected LEDs. Each segment would have
needed around 3 rows of 40, so a single digit was 7 x 3 x 40 =
840 LEDs. At the time that was around $160. Plus the PCBs
and components was another $100 / digit. For a 6-digit display
total came in at around $1500 + assembly costs + housing + PSU.
Ouch.

I thought it would be far simpler and cheaper to use magnetic
segments made of aluminium. One side is black, the other side
is fluoro-yellow, and they can be flipped using a (home-made ?)
solenoid pulling a lever. They can also be made larger with no
increase in cost. A good source of thin aluminium sheet is printing
plate. Ask at any decent-sized printers, they throw a lot out

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