Getting the Light Right for Shift Workers

Introduction

The human circadian system regulates our bodies’ various physiological rhythms, affecting hormone levels and our sleep-wake cycles. Lighting, particularly what is perceived by our eyes’ non-image forming photoreceptors or photosensitive retinal ganglion cells (ipRGCs), is a key environmental cue for keeping these rhythms in sync. Lighting dominated by higher frequencies and intensities (such as daylight), are stimulating and promote alertness, which is important as we start our day. Conversely, a lack of this stimulus signals the body that it’s time to slow down and get ready for rest, important as we end our day.

As we spend over 90% of our time indoors, the installation of lighting systems capable of mimicking in some manner the changing frequencies and intensities of daylight over the course of the day and year have the potential for improving our circadian health. However, obtaining this benefit is more problematic for shift workers, whose wake/sleep cycles are out of sync with the natural day/night cycle. Shift work refers to any work schedule that occurs outside of the traditional 9 AM – 5 PM work day. It can consist of early morning, evening or night shifts, and they may be regularly scheduled or rotating shifts. Research suggests that shift work is associated with insomnia, lower performance and an increased risk of workplace injuries, cardiovascular diseases, metabolic syndrome, diabetes, autoimmune hypothyroidism, and specific types of cancer (Boudreau 2013).

Lighting offers the potential to mitigate some of the negative impacts associated with shift work, but not surprisingly there is some disagreement among researchers and manufacturers as to the best way to approach meeting our circadian rhythm needs, particularly relative to shift work. Rotating shift workers pose the greatest challenge in that they’re unable to adapt their circadian rhythms to a set deviation from the natural day/night rhythm. For them the question becomes what is the best combination of lighting intensity and lighting frequency (wavelength) needed to create alertness while avoiding a large shift in their circadian rhythm, which might create re-adaptation problems once the short term shift ends or rotates to another shift.

• Long-term, regularly scheduled shift work: During the shift work, use higher illumination levels and lighting dominated by higher frequencies / shorter wavelengths (cooler light color temperatures with 460–480 nm [6500 – 6250K] having the most intense affects), particularly during the first half of the shift. This will help promote alertness as well as adaptation of the circadian rhythm to the long-term regularly scheduled shift work.
• Long-term, regularly scheduled shift work: Particularly when the goal is to adapt the circadian rhythm, it is important for employees to minimize the amount of light entering their eyes when not working. Total darkness while sleeping is recommended and other light source exposure should be limited to lower illumination levels and lower frequencies / longer wavelengths (warmer light color temperatures).
• Short-term and/or rotating shift work: Use higher illumination levels at the beginning of the shift work to support alertness. As it isn’t possible to adapt the circadian rhythm to the shift work in this case, it is recommended that the use of higher frequency / shorter wavelength light sources is limited and higher alertness obtained primarily via the higher illumination levels.
• Best practices for sleep: Companies should consider educating their shift workers on best practices for their quality of sleep during non-work hours. BranchPattern can assist with this, though other consultants may also be needed.
• Illumination levels: Based on various studies, a level of 1000 lux is considered sufficiently bright enough to artificially suppress melatonin production and promote alertness. The WELL Building Standard recommends a minimum of 250 equivalent melanopic lux (EML), measured on the vertical plane facing forward, 1.2 m [4 ft] above the finished floor. Targeting 1000 lux horizontal and 250 EML vertical using a light source between 5500-6500K color temperature represents a good starting point. BranchPattern can assist in determine the final values dependent on a client’s specific circumstances.
• Lighting System: A dimmable, tunable LED lighting system is recommended to provide the flexibility needed in creating the artificially illuminated environment necessary for meeting circadian rhythm needs relative to the type of shift work occurring. BranchPattern can assist with this recommendation.

Human Centric Lighting

• Varied Shift vs. Consistent Night Shift Work:
  “For workers who have varied shifts, it is not possible for the circadian rhythm to adapt to a solid deviation from the natural rhythm of day and night. In this case it is highly useful to use higher illumination levels at the beginning of shifts to support activity and alertness. For workers who consistently work night shifts it is also useful to use higher illumination levels as well as cooler light colour temperatures, both of which help to entrain the circadian rhythm to the unnatural sleep/wake cycle.”

From Lucas et al. (2014:9):

• Should Lighting Design Maximize or Minimize the Body’s Non-Visual Responses:
  “An important note of caution here is that it is not always clear whether lighting design should aim to maximize or minimize non-visual responses. In many ways, light can be considered a drug, having the potential for both beneficial and deleterious effects. These conflicting effects can occur concurrently, and in a single individual and context. For example, for night-shift workers, bright workspace lighting may improve immediate job performance by enhancing visual perception and promoting alertness, but suppress melatonin and shift the circadian clock to an undesirable phase. Conversely, dimmer lighting may minimize effects on circadian timing, but may be detrimental to more immediate performance.”
• Minimizing the Body’s Non-Visual Responses:
  “If the broad objective is to minimize the activation of ipRGC outputs, the goal should be to keep retinal irradiance as low as possible. There is no established threshold below which these systems are completely blind to light, so total darkness during sleep may be ideal where practical. Likewise, with respect to the visible spectrum, any wavelength can, in principle, activate the system. However, given that the relative sensitivity of these non-visual responses is generally reduced in the longer visible wavelength range, light sources should be biased toward longer visible wavelengths, to the extent consistent with other demands.”
• Promoting the Body’s Non-Visual Responses:
  “Conversely, if the objective is to promote ipRGC photoreception, retinal irradiance should be increased (within acceptable safety limits) and light sources may be biased towards the blue and blue/green regions of the visible spectrum, to which all photoreceptive inputs to this system are fairly sensitive.”

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From Arendt (2010):

• Increasing Light Levels & Short Term Shift Work:
  “The problem is that increasing light at night in short term shift work leads to improved alertness, performance and possibly metabolism, while no doubt increasing melatonin suppression. At present, investigations are proceeding on the use of glasses, which can block the short wavelengths most likely to suppress melatonin while hopefully maintaining alertness and performance.” – p. 16
• Manipulating Circadian Rhythms:
  “Light of suitable spectral composition and intensity can be used to adjust the timing and probably amplitude of circadian rhythms. The hormone melatonin can also act as a zeitgeber (vide supra). Light treatment during the first half of biological night prior to the melatonin peak will delay circadian rhythms and during the latter half, after the melatonin peak, will advance rhythms (Figure 2). Melatonin treatment by contrast advances rhythms in the first half of biological night and delays them in the latter half.” – p. 16
• Trickiness of Manipulating Circadian Rhythms:
  “An alternative approach has been described recently. This is to shift the circadian system, using timed light and melatonin, just to the point where the melatonin peak falls within the sleep period, avoiding large shifts which lead to readaptation problems [34,89]. This strategy appears to provide benefit for sleep, alertness and performance. However, if the timing is wrong, the opposite of the desired result will be produced. For example, instead of adapting to an 8 h advance in work time by advancing the clock, the system may delay. Avoidance of light at the wrong time is possibly more important than the light treatment itself.” – p. 17

From Canazei et al. (2016: abstract):

• Impacts of Polychromatic White Light:
  “To our knowledge, the present study for the first time demonstrates that polychromatic white light with reduced short wavelengths, fulfilling current lighting standards for indoor illumination, may have a positive impact on cardiac physiology of night-shift workers without detrimental consequences for cognitive performance and alertness.”

From Rashid and Zimring (2010:161):

• Lighting Impacts on Shift Workers:
  “Improvements in productivity, a decrease in accidents, an increased level of mental performance, improvements in sleep quality, and an increase in morale among night shift workers have been attributed to better lighting conditions (Luo, 1998).”
• Lighting Impacts on Shift Workers:
  “Increased lighting has shown to increase arousal level and alertness for shift workers (Campbell & Dawson, 1990).”