Chromatin organizes genetic material into multiple nuclear compartments. Euchromatin correspond to a state of open chromatin in which nuclear proteins can access easily whereas heterochromatin refers to a condensed state of chromatin that is less accessible and is generally described as the regulator gene silencing. However, regions of heterochromatin, constitutive heterochromatin, are comprised of repetitive non-coding regions. These highly compact sites are regulated by the self-association of heterochromatin protein 1 (HP1) while binding to the heterochromatin epigenetic mark H3K9me3. Alterations of constitutive heterochromatin have been associated with cancer and aging, however, the functional purpose of this non-coding compact region remains elusive. To explore this biological enigma, we designed a tool to control HP1 dimerization using blue light stimulation. By fusing HP1 with the optogenetic system CRY2, we are able to control HP1 oligomerization within minutes and create HP1 foci that consequently increase DNA quantity specifically at HP1 newly formed foci regions as well as reducing their accessibility to inert tracers. The light control of HP1 dimers enables us to explore the stability of heterochromatin regions and how expanding heterochromatin structures can affect nuclear and cellular integrity.