A system for photocleaving and scanning nucleotide analogs comprising: a) a substrate comprising a plurality of wells which each contain, or are configured to contain, a reaction mixture comprising a template nucleic acid, a polymerase, a primer hybridized to said template, and a first nucleotide analog, wherein said primer comprises a 3' terminal nucleotide analog with a photolabile blocking group that terminates chain extension, and wherein said first nucleotide analog comprises: i) a first detectable moiety, and ii) a photolabile blocking group that terminates chain extension; and b) a light system component comprising: i) a light source in optical communication with said plurality of wells which provides: A) photocleaving light input that cleaves said photolabile blocking group when it is part of said primer; and B) scanning input light that produces an optical signal from said first detectable moiety after said first nucleotide analog is added to said primer by said polymerase; and ii) a light control component that activates said light source such that a plurality of deblock-scan cycles are generated, wherein each of said deblock-scan cycles comprise an initial deblock time period where at least a part of said photocleaving light input is passed into said plurality of wells, and a following scan time period where at least part of said scanning light input is passed into said plurality of wells, and wherein said deblock time period is between 25 and 150 mSec and said scan time is at least 200 mSec. a) a substrate comprising a plurality of wells which each contain, or are configured to contain, a reaction mixture comprising a template nucleic acid, a polymerase, a primer hybridized to said template, and a first nucleotide analog, wherein said primer comprises a 3' terminal nucleotide analog with a photolabile blocking group that terminates chain extension, and wherein said first nucleotide analog comprises: i) a first detectable moiety, and ii) a photolabile blocking group that terminates chain extension; and b) a light system component comprising: i) a light source in optical communication with said plurality of wells which provides: A) photocleaving light input that cleaves said photolabile blocking group when it is part of said primer; and B) scanning input light that produces an optical signal from said first detectable moiety after said first nucleotide analog is added to said primer by said polymerase; and ii) a light control component that activates said light source such that a plurality of deblock-scan cycles are generated, wherein each of said deblock-scan cycles comprise an initial deblock time period where at least a part of said photocleaving light input is passed into said plurality of wells, and a following scan time period where at least part of said scanning light input is passed into said plurality of wells, and wherein said deblock time period is between 25 and 150 mSec and said scan time is at least 200 mSec. i) a light source in optical communication with said plurality of wells which provides: A) photocleaving light input that cleaves said photolabile blocking group when it is part of said primer; and B) scanning input light that produces an optical signal from said first detectable moiety after said first nucleotide analog is added to said primer by said polymerase; and ii) a light control component that activates said light source such that a plurality of deblock-scan cycles are generated, wherein each of said deblock-scan cycles comprise an initial deblock time period where at least a part of said photocleaving light input is passed into said plurality of wells, and a following scan time period where at least part of said scanning light input is passed into said plurality of wells, and wherein said deblock time period is between 25 and 150 mSec and said scan time is at least 200 mSec. <EOS>