The circadian period of both DBA/2 and C57BL/6 mice under DD (filled symbols) and dim red LEDfb (open symbols). Lines show the mean period for each group. Overall, mice had longer period under LEDfb than DD (p < 0.025), and C57BL/6 mice had longer periods than DBA/2 mice (p < 0.01).
Hofstetter et al. Journal of Circadian Rhythms 2005 3:8 doi:10.1186/1740-3391-3-8