# Sensitivity of the Circadian Clock to the Spectrum of Evening Light in Early Childhood

> **NIH NIH F32** · UNIVERSITY OF COLORADO · 2022 · $72,971

## Abstract

PROJECT SUMMARY
Late sleep timing and evening sleep problems in early childhood increase the risk for poor behavioral and
health outcomes. Light is the primary zeitgeber of the circadian system, and even small amounts of evening
light can suppress production of the sleep-promoting hormone melatonin and delay circadian timing. The
spectrum of light – not just the intensity – may be a particularly relevant factor for determining sleep and
circadian timing in early childhood for several reasons: (1) children are more sensitive to evening light
exposure than adults due to differences in ophthalmological features, including larger pupils and clearer lenses
that increase light transmittance; (2) young children show robust melatonin suppression (~90%) following
evening bright light exposure; and (3) media use in preschoolers has increased dramatically in the last decade
and is associated with late sleep timing and bedtime resistance. Central to this research are also data from
older children, adolescents, and adults indicating the circadian system shows high sensitivity to short-
wavelength blue light. To date, however, the role of light spectrum in young children’s sensitivity to evening
light exposure and its differential impact on circadian physiology is unknown. This is the primary purpose of this
F32 research project.
In a within-subjects crossover design, participants complete a 10-day protocol twice. Healthy, good sleeping
children aged 3.0-4.9 years maintain a stable sleep schedule for 7 days, followed by a 3-day in-home circadian
assessment performed in dim-light conditions. Children experience two counterbalanced experimental
conditions: a high CCT (5000K; blue-enriched) or low CCT (2700K; red-enriched) light exposure of 100 lux for
1-h before their scheduled bedtime. Following a 1-2 week “washout period”, the protocol is repeated with the
remaining condition. We will examine the impact of light spectrum on melatonin suppression (Aim 1) and
circadian phase shift (Aim 2). Dim light melatonin onset is assessed through saliva using our established
protocol to determine % melatonin suppression and circadian phase delay. The results of this proposal will
identify modifiable components of children’s evening light exposure (e.g. light spectrum and timing) to help
parents set limits and make healthy choices about their children’s lighting environment. Results are likely to
have high impact, as they will provide behavioral change recommendations that can minimize the negative
impacts of evening light exposure on children’s sleep duration and quality.
In addition to these research aims, this F32 Award will incorporate training in the measurement and analysis of
physiological measures, advanced statistical approaches, grant and manuscript writing, dissemination of
findings to the public, and lab management. The research and training proposed will be an important step in
facilitating Dr. Hartstein’s transition into an independent scientist with a research...

## Key facts

- **NIH application ID:** 10375368
- **Project number:** 5F32HD103393-02
- **Recipient organization:** UNIVERSITY OF COLORADO
- **Principal Investigator:** Lauren Hartstein
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $72,971
- **Award type:** 5
- **Project period:** 2021-05-01 → 2024-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10375368

## Citation

> US National Institutes of Health, RePORTER application 10375368, Sensitivity of the Circadian Clock to the Spectrum of Evening Light in Early Childhood (5F32HD103393-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10375368. Licensed CC0.

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