Crest 3D Whitestrips with Light's unique blue light system uses the same type of light technology dentists use. The blue light weakens stains so that the whitening ingredient can work more effectively. The result is dramatically better whitening compared to strips alone. #1 Dentist recommended at home whitening kit brand. Satisfaction Guaranteed - If you are not satisfied with your results, Crest will send you a pre-paid card in the amount of your purchase. Simply return your receipt and package UPC within 60 days of purchase. Limit to one refund per person. Call 1-800-208-0169 for more information.