Inclusion criteria:
Age 18–40 years.
Ability to understand study procedures and provide written informed consent.
Habitual digital-device use for at least one hour after sunset on at least five evenings per week.
Stable habitual sleep schedule during the preceding month, with bedtime and wake time varying by no more than two hours on most days.
Willingness to wear each assigned study lens from 6:00 PM until bedtime for 10 consecutive days and complete the 10-day washout period.
Willingness to complete the daily sleep diary, exposure log, adherence record, and adverse-effect form.
Normal or corrected-to-normal visual acuity and no clinically significant ocular disease affecting visual function.
No uncontrolled systemic, psychiatric, or neurological condition likely to affect sleep or participation.
Agreement to maintain usual sleep habits, evening activities, caffeine intake, and digital-device use throughout the study.
Exclusion criteria:
Self-reported physician-diagnosed sleep disorder, including chronic insomnia, delayed sleep–wake phase disorder, obstructive sleep apnoea, restless legs syndrome, or narcolepsy.
Current night-shift or rotating-shift employment.
Travel across more than two time zones during the previous month or planned during the study.
Current use of melatonin, hypnotics, sedatives, stimulants, or other medications or supplements known to substantially affect sleep or circadian rhythms.
Uncontrolled psychiatric, neurological, endocrine, cardiovascular, or systemic disease that could influence sleep.
Significant ocular disease, uncorrectable reduced visual acuity, severe colour-vision deficiency, or ocular surgery during the previous three months.
Current use of tinted, photochromic, or blue-light-filtering spectacles that cannot be discontinued during the intervention periods.
Hazardous alcohol use, defined as more than 14 standard drinks per week, or recreational drug use.
Participation in another clinical study that could influence sleep outcomes.
Inability or unwillingness to comply with the lens-wearing schedule or complete the required records.