Background: Delay in handling blood samples lead to inaccurate results because they may be exposed to light causing analyte degradation. The photodegradation of bilirubin will result in clinically significant changes in concentrations of bilirubin, this change might affect the clinical circumstances for which the test was requested. This study was done to determine the effect of light on plasma bilirubin concentration. Methods: Blood samples of normobilirubinemia and hyperbilirubinemia were drawn from neonates and adults, tested for total and direct bilirubin concentration at different time intervals after exposure to laboratory light using DMSO photometric method. Results: the study showed that, total, direct and indirect bilirubin levels are decreased after 2-hours and then the levels were markedly decreased after 4 and 6-houres. In adults with hyperbilirubinemia, the maximum decrease after 6-hours delay was 5.8mg/dl, 2.8mg/dl and 2.33mg/dl in total, direct and indirect bilirubin respectively. In adults with normal bilirubin levels the maximum decrease after 6 hours delay was 0.39mg/dl, 0.14mg/dl and 0.24 mg/dl in total, direct and indirect bilirubin respectively. In neonates with normal bilirubin, the maximum decrease after 6- hours was 1.8mg/dl, 0.53mg/dl and 1.3 mg/dl in total, direct and indirect bilirubin respectively. In neonates with hyperbilirubinemia, the maximum decrease in total bilirubin was 3.3mg/dl after 6-hours, in indirect bilirubin the maximum decrease was 2.4mg/dl while in direct bilirubin the maximum decrease was 0.79mg/dl after 6-hours delay. There was significant difference observed in mean results of all samples except for adult indirect hyperbilirubinemic samples after 2-hours exposure (P = 0.308). Conclusion: This study confirms that exposure of blood samples to laboratory lighting lead to statistically significant lowering of plasma bilirubin level.