Proper selection of letter height is critical to ensure a sign is legible to its intended audience. To make sure you select the correct letter height, Fire House Neon Signs has included a useful visibility chart that shows an approximate letter size required to be legible at a designated distance from the sign.
Calculations based on an externally (or naturally) lit sign with all uppercase letters. Factors that may affect required letter size include: color scheme, font selection, traffic and weather conditions. Please refer to the complete study by the Pennsylvania Transportation Institute, Penn University and the United States Sign Council.