Why have 4", 10 cm tall numbers.

This link gives information regarding the visibility of numbers. Numbers below 4" or 10 cm in height are too small for reliable visualization from longer distances especially at night. Added to this problem are the issues of contrast, visualization during day and night time hours. Solar-ID numbers are white on black contrast. The number is outlined with 8-12 brght LEDs giving superior night time visibility compared to back lit outlined numbers or indirect lighting of numbers or letters at night.