Dim light at night attenuates the amplitude of clock gene expression in the hypothalamus and liver. Transcripts of the core circadian clock genes Clock, Bmal1, Per1, Per2, Cry1, and Cry2 were analyzed by quantitative PCR in the (A) hypothalamus (B) hippocampus, (C) white adipose tissue, and (D) liver. Tissues were collected every 4 hr from mice exposed to either dark (black lines) or dimly lit (dotted lines) nights for 4 weeks. Values are expressed as relative abundance (mean ± SEM) after normalization to 18S *indicates dim light differs from dark nights.