The more premature the baby, the more sensitive to light they are – but in all cases, continuous bright lighting should be avoided. A supportive light environment helps to reduce levels of cortisol, extends sleep duration, stimulates the release of growth hormones and encourages the early development of a circadian rhythm.^2,3 Today, three approaches are commonly used in the NICU:

• Cyclical light exposure: usually has a night time phase and a daytime phase of 12 hours each 
• Adjustable dimmed lighting: the light is turned down whenever the baby is asleep
• Continuous dimmed lighting: the light is always dim

Cycled lighting, imitating the circadian rhythm, has been shown to be the most beneficial approach. Babies exposed to cyclical lighting show better growth and hormone regulation. They are less anxious, cry less, sleep better and are more active during the day.^4,5 Some studies show that continuous dim light may, in fact, be just as bad as continuous bright light.⁶ The underlying idea for the constant dim light approach is that it’s also dark in the uterus. However, a foetus does experience a rhythm due to increased activity, higher noise levels and different lighting during the day and night. In addition, a minimum amount of light is necessary for staff to carry out reliable work – for example, when measuring skin colour during jaundice checks. Continuous dim lighting can also lead to higher stress in parents and staff spending nights in the neonatal unit.⁷

Because of the unequivocal benefits premature babies get from cycled lighting, there are now clear recommendations for introducing it into NICUs. The light should be infinitely adjustable within the range of 10 to 600 lux and spotlights should be used for individualised lighting. However, it’s not always easy to implement such practices in day-to-day clinical practice. The direction of light, the thickness of the incubator walls, whether the incubator is open and the type of cover it has all play a role in how much light the babies are actually exposed to – and so it becomes a difficult job to accurately estimate this.