The Rockefeller Foundation is providing support to this Seeker to design an indicator which gives the user a visual sign of having been exposed to a sufficient dose of sunlight or UV-light. It is part of the Global Giveback Innovation Challenge Set. The submission to the Challenge should include the following: The detailed characterization of the proposed indicator addressing specific Solution Requirements presented in the Challenge description. This description should be accompanied by a well-articulated rationale supported by literature/patent precedents. Experimental data demonstrating the desired properties of the proposed indicator obtained as described by the Seeker. The Seeker is not looking for just a review on the subject. The proposed indicator should offer the Seeker "freedom to practice", i.e. there should be no patents or patent applications preventing the use of the solution. The award is contingent upon the evaluation of the submitted solutions by the Seeker.