The present study is part of a larger work aiming at establishing the knowledge basis needed to develop cost-effective processes for producing high-bright mechanical and chemimechanical pulps. The influence of process conditions (time, pH, temperature, consistency) on the optical properties during pulp storage of a well-washed hydrogen peroxide bleached Norway spruce pulp has been examined. The general effect of storage was darkening of the pulp due to an increase in light absorption, especially at shorter wavelengths. Time and temperature were found to be the process variables that had the largest impact, the trends were similar independent of pH and pulp consistency. The light scattering ability increased initially, giving a positive contribution to brightness. This indicates that the storage also resulted in a change in sheet structure.