As more time passes, there is a higher chance that the photons will split an unbleached photopigment because the rate of regeneration will have surpassed the rate of bleaching.
One of the most visible uses for unbleached kraft pulp is to make brown paper shopping bags and wrapping paper where strength is particularly important.
This occurs several times, to ensure that all accessible fluorophores are bleached since unbleached fluorophores are exchanged for bleached fluorophores, causing movement through the cell membrane.
