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. 2023 Nov 21;4(1):zpad051.
doi: 10.1093/sleepadvances/zpad051. eCollection 2023.

Hybrid effectiveness-implementation study of two novel spectrally engineered lighting interventions for shiftworkers on a high-security watchfloor

Sara C Bessman  1   2 , Elizabeth M Harrison  1   2 , Alexandra P Easterling  1   2 , Michelle N Snider  1   2 , Sebastian M M Preilipper  1   2 , Gena L Glickman  2
Affiliations

Hybrid effectiveness-implementation study of two novel spectrally engineered lighting interventions for shiftworkers on a high-security watchfloor

Sara C Bessman et al. Sleep Adv. .

Abstract

Shiftwork leads to myriad negative health and safety outcomes. Lighting countermeasures can benefit shiftworkers via physiological effects of light (e.g. alerting, circadian adjustment), and short-wavelength light is the most potent for eliciting those responses; however, limited work indicates it may not be required for alerting. We developed similar-appearing light boxes (correlated color temperature: 3000-3375 K; photopic illuminance: 260-296 lux), enriched (SW+, melanopic EDI: 294 lux) or attenuated (SW-, melanopic EDI: 103 lux) in short-wavelength energy, and implemented them on a high-security watchfloor. Efficacy and feasibility of these two novel lighting interventions were assessed in personnel working 12-hour night shifts (n = 47) in this within-participants, crossover study. For each intervention condition, light boxes were arranged across the front of the watchfloor and illuminated the entire shift; blue-blocking glasses were worn post-shift and before sleep; and sleep masks were used while sleeping. Comparisons between baseline and intervention conditions included alertness, sleep, mood, quality of life (QOL), and implementation measures. On-shift alertness (Karolinska Sleepiness Scale) increased in SW- compared to baseline, while changes in SW+ were more limited. Under SW+, both mood and sleep improved. Psychomotor vigilance task performance did not vary by condition; however, perceived performance and QOL were higher, and reported caffeine consumption and sleep onset latency were lower, under SW-. For both interventions, satisfaction and comfort were high, and fewer symptoms and negative feelings were reported. The addition of spectrally engineered lights to this unique work environment improved sleep, alertness, and mood without compromising visual comfort and satisfaction. This paper is part of the Sleep and Circadian Rhythms: Management of Fatigue in Occupational Settings Collection.

Keywords: alertness; circadian; implementation; intervention; light; melanopic; shiftwork; sleep; spectrum.

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Figures

Figure 1.
Figure 1.
Spectrally engineered lightboxes. Spectral power distributions are provided for (A) SW+ and (B) SW- light boxes, along with associated irradiance, alpha-opic equivalent daytime illuminances (e.g. rhodopsin [rho] and melanopic [mel]), and correlated color temperature for each.
Figure 2.
Figure 2.
Study protocol. (A) An overview of the two, 16-day intervention periods for a sample participant who had their first baseline assessment prior to SW+ and their second baseline assessment after SW- is represented in this diagram. Each box represents 1 day, including baseline night shifts (yellow), days off (white), SW+ night shifts (blue), and SW- night shifts (red). Blue-blocking glasses and sleep masks were worn during intervention weeks only. The 16-32-day washout period is not shown. (B) The schedule of assessment for the study is illustrated for the second work night in a series of night shifts. Throughout the baseline and intervention conditions, an actigraph watch was worn continuously, and a sleep diary was completed daily. Psychomotor vigilance task (PVT) and Karolinska Sleepiness Scale (KSS) assessments occurred near the beginning, middle, and end of the night shift, with an additional KSS completed immediately after the shift. Email and/or text message reminders are depicted with arrows and were sent throughout.
Figure 3.
Figure 3.
Watchfloor schematic and baseline light. (A) This diagram represents a schematic of the watchfloor space, including key dimensions. The front of the space contained a row of three oversized monitors (thin white rectangles) suspended well above the surface upon which six of either SW+ or SW- light boxes were arranged underneath, unobstructed, in the same configuration (thicker yellow rectangles), all facing into the room. The front row of four workstations (dashed boxes) is where the vast majority of participants spent most of their time; two additional workstations were located behind those, and all workstations directly faced the oversized monitors (which required regular attention of participants) and lightboxes. In total, there were ~45 computer and television monitors under the control of watchfloor staff that varied somewhat in size, intensity, and color temperature; only the three oversized ones are depicted here. (B) The spectral power distribution as well as irradiance, alpha-opic equivalent daytime illuminances (e.g. rhodopsin [rho] and melanopic [mel]), and correlated color temperature are averages of measurements taken for baseline conditions from the front ledge of the desk at the front row of workstations from a seated position at eye-level, with the meter directed toward the center of the nearest lightbox (all turned off) and avoiding a direct line with any surrounding monitors.
Figure 4.
Figure 4.
Sample actogram of sleep, activity, and light patterns from a single participant. Days are on the vertical axis, and time of day is on the horizontal axis, with representations of relative timing for activity (black markings), sleep (blue shading), and photopic lux (yellow lines). This particular participant received the study conditions in the following order: Baseline, SW+, SW-, Baseline. The 16-day interval of working day shifts between the two intervention weeks is cropped out of the figure for ease of viewing.
Figure 5.
Figure 5.
Sleepiness/alertness across the shift and by condition. Estimated marginal mean Karolinska Sleepiness Scale (KSS) scores from participants at the beginning, middle, and end of night shifts (up to 4 nights per person per condition), with bars representing baseline (BL; black), SW+ (blue), and SW- (red) conditions. Sleepiness varied by condition (F(2,1179.98) = 8.60, p < 0.001), with lower sleepiness scores in the SW- condition as compared to both BL (p < 0.001) and SW+ (p < 0.05). Sleepiness also increased across the shift (F(2,1168.55) = 290.87, p < 0.001), with lowest values at the beginning of the shift, intermediate in the middle, and highest at the end of the shift (all p < 0.001). There was also a significant condition by time-on-shift interaction (F(4,1168.07) = 2.45, p < 0.05), likely driven by the changing relationship between SW+ and BL scores across the shift.
Figure 6.
Figure 6.
Mid-shift PVT performance across conditions. Estimated marginal means for the psychomotor vigilance task (PVT) (A) mean reaction time and (B) errors are shown for baseline (BL), SW +, and SW-. There were no effects of condition on any PVT variable examined (all p > 0.12).
Figure 7.
Figure 7.
Brightness, comfort, and satisfaction with the light boxes by condition. Estimated marginal means of responses on a five-point scale (1–5) administered in the weekly (every 8 days) questionnaire are shown for baseline (BL), SW+ , and SW-. (A) Participants had higher satisfaction under both intervention conditions than in baseline (F(2, 69.78) = 12.65, p < 0.001; p < .001 for SW + and p < 0.01 for SW-). Additionally, they found (B) the light boxes in both conditions to be less bright (F(2, 70.07) = 7.60, p < .001; p < 0.01 for both SW+ and SW-), and (C) more comfortable (F(2, 69.96) = 16.06, p < .001; p < 0.001 for SW + and p < 0.01 for SW-), as compared to baseline conditions.
Figure 8.
Figure 8.
Mood, feelings, and symptoms attributed to the light boxes by condition. Participants endorsed feelings they attributed to the light boxes (sad, anxious, sleepy, wired, alert, excited, happy, relaxed, and none) and any symptoms attributed to the light boxes (glare, headache, nausea, and fatigue), after each condition in the ~weekly (every 8 days) questionnaire for baseline (black), SW+ (blue), and SW- (red). (A) There were more headaches, glare, and fatigue in baseline conditions than in both intervention conditions (both p < 0.01, p < 0.001, and p < 0.001 for headaches, glare, and fatigue, respectively), and (B) fewer people endorsed feeling sad and anxious in both intervention conditions as compared to baseline (all p < 0.05). Additionally, more people endorsed a positive mood (happy [p < 0.05], relaxed [p < 0.01]) in SW+ as compared to baseline.
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