Impact of blue-depleted white light on pupil dynamics, melatonin suppression and subjective alertness following real-world light exposure

Jamie M Zeitzer,Cheng-Ann Wang,Mirelle Kass,Raymond P Najjar

doi:10.1186/s41606-018-0022-2

Abstract

BackgroundThe non-image forming system, which conveys light information to circadian and sleep centers in the brain, is optimized to respond to short wavelengths of light (blue). Exposure to white light with reduced blue content can cause lower than expected circadian and sleep responses. These findings, however, come from controlled laboratory conditions that may not be entirely accurate when attempting to apply them to most real-world settings. It was our intention to examine whether, under ecologically-valid circumstances, a blue-depleted white light had a diminished impact on sleep and circadian functions as compared to an equiluminant white light.MethodsIn Study 1, seven healthy, young individuals were exposed to a series of one-minute light pulses (32, 100 or 140 lx) produced either by a standard white light emitting diode (LED) or an LED light with reduced blue content. Pupil responses were measured with an infrared pupillometer. In Study 2, ten healthy, young individuals participated in two overnight evaluations. On one of the nights, participants received three hours of 150 lx of a standard white LED starting at habitual bedtime. The protocol on the alternate night was identical except an LED with reduced blue content was used (both lights were identical to those used in Study 1). Saliva samples were collected every 20–30 min for determination of melatonin concentrations and subjective sleepiness was assessed hourly with the Stanford Sleepiness Scale. In both studies, pre-light exposure baseline was real-world ambulatory light exposure.ResultsStudy 1. The post-illumination pupil response (PIPR) to 32 lx was increased in response to the standard as compared to blue-depleted LED (p < 0.05, paired t-test). PIPR did not differ between lighting conditions at higher illuminances. Study 2. Neither salivary melatonin concentrations nor subjective sleepiness scores were different between lighting conditions.ConclusionsWhile the absence or reduction of blue light has the physiologic capacity to reduce the impact of light on non-image forming photoreceptive functions, under a pre-exposure lighting environment closer to that which is found in the real world, no such differences are observed except for pupil responses to moderately dim light.Trial registrationClinicalTrials.gov #NCT02936674, NCT02636140.

Highlights

The non-image forming system, which conveys light information to circadian and sleep centers in the brain, is optimized to respond to short wavelengths of light
Melanopsin has a peak sensitivity in the blue range of the light spectrum (Newman et al, 2003) and the spectral sensitivity of sustained melatonin suppression peaks in the blue light range (~ 460 nm) (Brainard et al, 2001)
Study 1 Following the stable pupil size observed under conditions of darkness, the pupil rapidly constricted to a minimum size in response to both lights (Fig. 2)

Summary

Introduction

The non-image forming system, which conveys light information to circadian and sleep centers in the brain, is optimized to respond to short wavelengths of light (blue). It has been theorized that exposure to broad spectrum white light that has been depleted of or has minimal short wavelengths (blue light) would not alter conscious visual perception but would minimally activate non-image forming photoreceptive functions (McBean et al, 2016). This would be notable for extended (hours) light stimuli as the response to shorter light stimuli is likely more driven by cones (Gooley et al, 2010). Participants spent 8 h in moderate room lighting (~ 88 lx) prior to receiving the experimental light which likely sensitized the responses to the low intensity light (Smith et al, 2004; Chang et al, 2011)

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