There are great advantages in cost and simplicity, if exposure sources in lithography systems for printing two dimensional code marks are changed from ultra-high-pressure mercury lamps to light emitting diodes (LEDs). For this reason, a prototype exposure system was developed, and it was demonstrated that two dimensional code marks were successfully printed using LEDs as exposure sources and a squared plastic optical fiber matrix as code-mark cells. In addition, it was also verified that suitably printed code marks were directly readable using a commercially available code-mark reader. However, readability for various marks has not been investigated sufficiently. For this reason, the readability was investigated in detail by variously changing lighting maps of LEDs, here. Readable ratios of code marks printed under short exposure-time conditions were investigated in particular to clarify the redundancy and margin for the exposure dose and mark-quality degradation. As test code marks, 6 figure numbers such as 111111, 222222,…777777 were used. This is because not to make LEDs which are not lightened. As a result, all the code marks printed with good profiles and almost no resist residues were correctly read. In addition, code marks with slight resist residues were also readable. It was clarified that amount of resist residues in the data area greatly influenced the readability.