Sensitive components of foods may undergo degradation reactions when subjected to light. The packaging of the food may slow down such reactions by absorbing and reflecting a fraction of the incident light. Riboflavin is a typical light-sensitive nutrient and undergoes first-order degradation when subjected to light. Rate constants of this reaction were evaluated under 25W, 60W, 100W and 200W white light bulbs at pH = 8, at 20 +/- 1-degrees-C, with no light shielding or by shielding the light with a single fold of high density polyethylene or two folds of low density polyethylene films. Numerical values of the reaction rate constants were proportional to the light source power and varied with the number of polymer films. The proportionality constant was regarded as the 'protection index' of the specific film. The results implied that the smaller the protection index of the film the smaller was the degradation reaction rate constant. Although this study was done by employing two different kinds of polymer films and one light-sensitive chemical only, this approach may be employed for comparing the packaging efficiency of polymers used for wrapping foods containing light-sensitive components.