Light sources for roadway lighting are being converted from High Pressure Sodium (HPS) luminaires to Light Emitting Diode (LED) luminaires because they are energy efficient and offer better visibility. LEDs with higher (greater than 3000K) correlated color temperature (CCT) often have higher blue content in their spectrum (460 to 480 nm) than conventional High Pressure Sodium (HPS) lamps. Light in this wavelength affects the production of the hormone melatonin, which regulates the human circadian rhythm. Melatonin increases drowsiness, and it is naturally produced late in the evening until the early morning in humans. Recently, the American Medical Association (AMA) reported that roadway lighting with higher blue content such as the light produced by LEDs could adversely suppress melatonin and affect the sleep health of people (drivers, pedestrians etc.) exposed to it. However, a definitive link between melatonin suppression and roadway lighting has never been reported. Alternatively, there could also be an advantage of the blue content in the LEDs. Since the blue content in LEDs suppresses melatonin, it has the potential to reduce driver drowsiness and make them more alert. In order to design effective roadway lighting, research is needed to understand the relationship between melatonin suppression and driver drowsiness and health caused by LED roadway lighting. This research will lead to better lighting recommendations that will mitigate any harmful health effects of LED lighting while making drivers more alert.
The objective of this research is to evaluate the effect of the LED roadway lighting on the health and alertness of drivers. The research shall examine the main factors that may influence melatonin suppression in humans, viz., the strength of blue content in the light, the light level or intensity, and the dosage or duration of exposure. The strength of the blue content is dictated by the correlated color temperature (CCT) of the light sources. LED lights with CCTs greater than 3000K have stronger blue content than those below that threshold. It is also important to understand if the light levels experienced in nighttime roadway lighting influence melatonin suppression. Finally, the effect of duration of exposure or dosage on the suppression of melatonin shall be addressed. Understanding the role of dosage will help in determining limits of acceptable exposure to the roadway lighting. Dosage limits will also have important implications for adaptive lighting of roadways.
Note: In approving this project, the AASHTO Standing Committee on Research directed NCHRP to engage an expert from the NASEM Health and Medicine Division as a project panel member.