Provided herein are systems and methods for nucleic acid sequencing by synthesis in a plurality of wells using detectably labeled chain terminating nucleotides with photolabile blocking groups and pulses of photocleaving light. In certain embodiments, the systems and methods provides a plurality of deblock-scan cycles comprising an initial deblock time period followed by a scanning light period, wherein at least one of the following occurs in each deblock-scan cycle: 1) the deblock time period is shorter than the scan time period; 2) the deblock time period is only long enough to deblock the photolabile groups that are part of a primer in less than all of the plurality of wells; or 3) the deblock time period is between 25 and 150 mSec and the scan time is at least 200 mSec. Such shorter deblock time periods help prevent the addition of more than one nucleotide to the primer prior to scanning (e.g., accuracy is enhanced).