Implementation of the Light Regularity Index in the pyLight submodule

[Manuel Spitschan]

In a publication (preprint PDF here) in Sleep, Hand and colleagues recently proposed the Light Regularity Index.

From their paper:

Inspired by the formulation of the SRI, we devised an equivalent metric for light. First, we converted the light time series into a binary signal (similar to sleep vs. wake), based on whether the light level was above or below an absolute threshold (i.e., 10, 20, 50, 100, 300 and 500 lux). The LRI was then calculated by determining the probability that an individual was in the same state (above vs. below a threshold) at any two time points, 24 hours apart. The index was scaled so that an individual who records light exposure greater than their median light level at exactly the same times each day would score 100, whereas an individual who records random light exposure patterns would score 0. Participants whose LRI value was calculated using less than 5 days of overlapping valid epochs were considered missing for that period (school = 0.00%; vacation = 2.00%).

It would be a great addition to pyActigraphy.