Artificial light at night (LAN) reduces the natural darkness and negatively impacts behavior, physiology, and higher brain functions in both captive and wild animals. The inevitable widespread usage of LAN exposure is usually from the broad spectrum dim LAN (dLAN). Here, we investigated whether a monochromatic light would affect the dLAN-induced effects on sleep, metabolism and oxidative stress in a diurnal vertebrate, the zebra finch (Taeniopygia guttata). Birds were maintained on 12 h of broad-spectrum light (150 lux, 1.426 W/m²) coupled with 12 h of complete dark night or dLAN at an identical intensity (5 lux, 0.048 W/m²) of broad spectrum (400-700 nm), long (620 nm) and short (460 nm) light wavelengths. Light wavelengths affected the dLAN-induced intermittent awakenings and advanced morning wakeups, hence a shorter and poorer sleep, with concurrent changes in the hypothalamic gene expression patterns. In particular, the mRNA expressions of sik3 and achm3 genes were consistent with wavelength effects on the awake state promotion, and those of dcx and bdnf genes were consistent with the sleep deprivation effects on the overall brain functioning. Further, dLAN-induced nocturnal feeding resulted in body fattening and weight gain, suggesting metabolic impairment in the broad spectrum and short wavelength but not the long wavelength dLAN. There were increased nocturnal hepatic g6pc and irs1 mRNA levels, indicating an elevated gluconeogenesis in both broad spectrum and short wavelength dLAN. We also found an enhanced oxidative stress, evidenced by elevated gpx and cat mRNA levels in the hypothalamus and blood, respectively, under both broad spectrum and short wavelength dLAN. These results highlight the wavelength-dependent effects of dLAN on sleep, metabolism, and oxidative stress in zebra finches, offering important insights into the broader consequences of nighttime light pollution for diurnal species, including humans inadvertently exposed to artificially lit urban environments.
