Many young children are exposed to light int he evening hours before bedtime. Children's biological clocks are highly sensitive to evening light exposure, which can delay the timing of the clock and make it harder to fall asleep. The purpose of this study is to test three strategies (adjustment to home lighting, amber-tinted glasses, clear glasses) to reduce evening light exposure in children ages 5-6 years with parent-reported sleep onset difficulties in order to improve their sleep and the timing of their biological clock. This study takes place over approximately 5 weeks. After baseline assessments of children's sleep timing, light exposure, cognition, and circadian rhythms, they will be randomly assigned to one of three interventions to reduce evening light exposure for two weeks. After the two-week intervention period, the baseline measures are repeated and parents are interviewed about their and their child's experiences with the intervention.

Evening sleep difficulties are common in young children and can contribute to behavioral and health problems. Sleep timing is regulated in part by the circadian clock, which is highly sensitive to light exposure. Light in the hour before bedtime can suppress melatonin, delay circadian timing, and make it harder for children to fall asleep. Despite evidence of high circadian sensitivity to evening light, few studies have tested interventions to improve sleep timing in early childhood using light-based strategies.

This study evaluates the feasibility, acceptability, and preliminary efficacy of two light-mitigation strategies to advance sleep and circadian timing in children aged 5 to 6 years with parent-reported sleep onset difficulties. Children will participate in a five-week study consisting of baseline assessments, a two-week intervention period, and post-intervention assessments. Parents of enrolled children will provide written informed consent for their child's participation. Children are under age 7 years and are not required to provide formal assent.

Baseline assessments will include sleep timing, duration, and quality measured via actigraphy, circadian phase assessed with salivary dim-light melatonin onset (DLMO), parent-reported sleep behaviors, and a cognitive battery. Children will then be randomly assigned to one of three interventions: (1) smart home lighting to reduce evening short-wavelength light, (2) amber-tinted glasses worn in the hour before bedtime, or (3) clear glasses as a sham control. Interventions will last two weeks, with adherence monitored throughout.

After the intervention, all assessments will be repeated, and parents will participate in structured interviews to report on the feasibility and acceptability of the assigned strategy. Exploratory measures will include baseline pupillary light response to examine individual differences in photosensitivity as potential moderators of intervention effects.

Data from this study will inform the feasibility and acceptability of light-based interventions in young children (Aim 1), provide preliminary evidence of effects on sleep and circadian timing (Aim 2), and explore whether photosensitivity moderates response to the interventions (Exploratory Aim 3).

Inclusion Criteria:

• Inclusion requires that children are aged 5.0-6.9 years at the time of enrollment with a parent-reported sleep onset of ≥ 60 min after parents' desired bedtime at least three nights per week.

One adult parent of each participating child will also take part in the study. Parents must be able to provide consent for themselves and their child and to complete the interview at the end of the study.

Exclusion Criteria:

• Children are excluded for the following reasons:

  • All sleep disorders as indicated on the telephone screener or by clinical cut-off scores on the Children's Sleep Habits Questionnaire (CSHQ), except for insomnia or DSWPD as features of these disorders are directly targeted by the intervention. Secondary analyses will explore if outcomes differ among participants with or without parent-reported symptoms consistent with these diagnoses.
  • Physical abilities that interfere with assessments (e.g., visual impairment), developmental disabilities (e.g., autism, attention-deficit/hyperactivity disorder (ADHD), pervasive developmental disorder), epilepsy or other neurological disorders, metabolic disorders, medical conditions that commonly require treatments or assessments during the night (e.g., cancer, diabetes, active asthma), current infection or lead poisoning; a head injury involving loss of consciousness in the past 6 months.
  • Current use of medications affecting daytime sleepiness, the circadian system, or light sensitivity.
  • Eye disorders or color blindness (determined with Ishihara Color Vision Test); corrected vision with eyeglasses is permitted.

No identifiable data will be shared. Only de-identified study data will be made available for research purposes.

Participants are blinded to study condition. Research staff are aware of assignment after baseline assessments. Laboratory technicians conducting melatonin assays are blinded to study hypotheses and participant condition.