The VIIRS day / night band (DNB) high gain stage (HGS) pixel effective dwell time is in the range of 2-3 milliseconds (ms), which is about on third of the flicker cycle present in lighting powered by alternating current. Thus, if flicker is present it can induce random fluctuations in nightly DNB radiances. This results in increased variance in DNB temporal profiles.
A survey of flicker characteristics conducted with a high-speed camera data collected on a wide range of individual luminaires found the flicker is most pronounced in high intensity discharge lamps such as high- and low-pressure sodium and metal halides. Flicker is muted but detectable in incandescent luminaires. Modern light emitting diode (LED) and fluorescent lights are often nearly flicker-free, thanks to high quality voltage smoothing.
DNB pixel footprint on the ground are about a half square kilometer and can contain vast numbers of individual luminaires, some of which flicker and others not. If many of the flickering lights are drawing from a common AC supplier – the flicker can be synchronized and leave an imprint on the DNB temporal profile. In contrast, multiple power supplies will throw the flickering out of synchronization - resulting in a cacophony with less radiance fluctuation. Examination of DNB temporal profiles for location of high intensity discharge (HID) to LED streetlight conversions show a reduction in the index of dispersion, calculated by dividing the annual variance by the mean.
There are a number of variables that contribute to radiance variations in the VIIRS DNB, including view angle, cloud optical thickness, atmospheric variability, snow cover, lunar illuminance, and the compilation of temporal profiles using pixels whose footprints are not perfectly aligned. It makes sense to adjust the DNB radiance for as many of these extraneous effects as possible. However, none of these adjustments will reduce the radiance instability introduced by flicker. Because flicker is known to effect organisms, including humans, the development of methods to detect and rate the strength of flickering from space will open up new areas of research on the biologic impacts of artificial lighting, as well as help to quantify the inherent uncertainty of various parameters, including environmental properties, based on the assumption of a known surface light characteristic.
When using the data please credit the product generation to the Earth Observation Group, Payne Institute for Public Policy.