I think I was looking for this link:
http://www.8052.com/forum/read.phtml?id=85155

Anyways I found lots of information searching for LED signs on this forum which will be summerized as follows:
1. Do not use multiplexing.
2. Use constant current LED driver ICs like the ST2221A.
3. Use photo sensor and control PWM on OE of driver's ICs to control brightness of LED sign for ambient light.
4. The eye's response to PWM is very non linear. So to get 8 relatively even steps of brightness use the following PWM schemes:

    7: 100.0% (brightest)
    6:  50.0%
    5:  25.0%
    4:  12.5%
    3:   6.3%
    2:   3.1%
    1:   1.7%
    0:   0.0% (off)

5. Separate VCC of microcontroller and VLED for LEDs draw large amount of current which might dip the voltage on the microcontroller.
6. load the data serially to the led board using 4 wires: SerIN, Strobe, Enable, Clock
7. Make the boards for a sign panel with a serial interface which makes the sign modular by daisy chaining the serial connections of each LEDs block.
8. Use of 6 layers for PCB is prefferable for 2 layers for PCB power, 2 layers for signals, 1 for logic power.
9. Use the following character sizes for corresponding distances: <pre>
Max Vewing Distance (m) Character Size(mm)
----------------------- -------------------
250 585

200 456

125 308

100 250

60 154

40 103

Did I miss something?
Mahmood