Bright-light before bedtime disrupts preschoolers sleep patterns, study suggestsExposing preschoolers to bright light before bedtime is not a good idea, according to a new CU Boulder study. It almost completely shuts down their production of the sleep-promoting hormone melatonin, keeping it suppressed for at least 50 minutes after light's out, says lead author Lameese Akacem with the Sleep and Development Laboratory.