Fig. 1

Artificial overhead lighting is present throughout the ICU and angle poise lighting is available on a stack at every bedside (a). A typical bed space in an open bay (bed absent). Note the window (i). A typical side-room with window (blind is down) (ii). A typical side-room without a window. Note the wall-mounted light box in place of a window (iii). Mean (±SEM) light intensity across ICU by day and night (b). Mean (±SEM) light intensity measured in different locations on ICU during the day and night (c). Fluctuating levels of light intensity are seen in an open bay bed space, which then gradually reduce over the day (d). Typical pattern of artificial lighting in a windowless side-room; a constant day-time light intensity of 180 lux, which abruptly reduces at night-time (e). A side-room with a window demonstrates a combination of natural and artificial lighting during the day (f). A low-intensity night-light has been left on for intervals overnight in (e) and (f). Overnight, there are several bright ‘pulses’ of light, indicating lights being switched on and off (d), (e) and (f)