There is provided a device (100) for treating tissue (102). The device (100) comprises a light source (104) configured to emit light (106) to illuminate the tissue (102). The light source (104) is configured to alternate between emitting light of a first wavelength to stimulate at least partial photoconversion of a protein in at least part of the tissue (102) and emitting light of a second wavelength to at least partially reverse the at least partial photoconversion of the protein in the at least part of the tissue (102). The first wavelength and the second wavelength are different.
