Effects of Personalized Lighting on Subjective Ratings, Cognitive Performance, and Physiological Stress Response in a Simulated Office Environment

Figures & data

Fig. 1. Diagram of the study protocol. Blue color indicates questionnaires, orange color indicates cognitive tests. Green indicates physiological measures. Tasks were completed in the order in which they are listed. PVT = psychomotor vigilance task - measures vigilance; NLT = number letter task – measures cognitive flexibility; PASAT = paced auditory serial addition task – measures attention and information processing speed; 2-back = working memory task – measures working memory capacity; PANAS = positive and negative affect scale – measures mood state; T1 = first measurement; T2 = second measurement; T3 = third measurement.

Fig. 2. Screenshot of the desktop user interface to personalize workplace lighting.

Fig. 3. Workplace lighting situation during the control condition (5300 K).

Table 1. Light settings under personalized lighting and the control condition. α-opic measurements were taken at eye level. CCT = correlated color Temperature; EDI = equivalent daylight illuminance.

	CCT (back wall)	CCT (desk)	CCT (at eye level)	Illuminance (back wall)	Illuminance (desk)	Illuminance (at eye level)	S-cone-opic EDI	M-cone-opic EDI	L-cone-opic EDI	Rhodopic EDI	Melanopic EDI
Mean	3259 K	3418 K	3299 K	1562 lx	2603 lx	924 lx	318 lx	573 lx	705 lx	426 lx	381 lx
SD	682 K	517 K	450 K	623 lx	1038 lx	234 lx	150 lx	182 lx	204 lx	159 lx	152 lx
Min	2300 K	2200 K	2252 K	540 lx	900 lx	540 lx	119 lx	281 lx	333 lx	220 lx	182 lx
Max	5300 K	4100 K	4359 K	2616 lx	4360 lx	1300 lx	714 lx	935 lx	1034 lx	801 lx	754 lx
Control condition	5300 K	5300 K	5174 K	493 lx	510 lx	109 lx	81 lx	103 lx	108 lx	92 lx	86 lx

Fig. 4. Melanopic EDIs (equivalent daylight illuminance) for each participant under personalized lighting. The dashed line indicates the melanopic EDI of the control condition (= 86 lx). The triangle in the violin plot signifies the mean EDI under personalized lighting.

Fig. 5. Scatter plot for self-selected CCTs (correlated color temperature). The dotted line indicates equal CCTs at the desk and the wall.

Table 2. Sleepiness, affect, and working memory. Data are mean ± standard deviation; PANAS = positive and negative affect Schedule; pre = before light exposure; post = after light exposure.

	Control Condition		Personalized Lighting
	Pre	Post	Pre	Post
Sleepiness	2.64 ± 1.09	3.05 ± .95	2.32 ± 1.17	3.05 ± 1.00
Positive affect (PANAS)	2.55 ± .70	2.23 ± .64	2.61 ± .73	2.16 ± .61
Negative affect (PANAS)	1.18 ± .19	1.16 ± .21	1.15 ± .27	1.12 ± .18
2-back task (total score)	4.39 ± 1.11	4.39 ± 1.28	4.33 ± 1.22	4.36 ± 1.15

Fig. 6. Changes in the PANAS (positive and negative affect schedule) positive affect ratings over time. Pre = before light exposure; post = after light exposure.

Table 3. Vigilance, task switching, sustained attention, and information processing performance during light exposure. Reaction speed is 1/reaction time. T1 = first measurement; T2 = second measurement; T3 = third measurement; SD = standard deviation; IQR = interquartile range. PVT = psychomotor vigilance Test; NLT = number letter Task; PASAT = paced auditory serial addition task.

	Control Condition			Personalized Lighting
	T1	T2	T3	T1	T2	T3
Vigilance – PVT
Reaction Speed (mean ± SD)	3.58 ± 0.45	3.49 ± 0.53	3.57 ± 0.49	3.52 ± 0.44	3.58 ± 0.42	3.59 ± 0.46
Number of Lapses (median and IQR)	0.00 (0.00–0.75)	0.00 (0.00–1.00)	0.00 (0.00–1.00)	0.00 (0.00–0.75)	0.00 (0.00–1.00)	0.00 (0.00–1.00)
Task switching – NLT
Reaction Speed
Non-switch (mean ± SD)	1.39 ± 0.15	1.42 ± 0.14	1.44 ± 0.12	1.39 ± 0.14	1.41 ± 0.13	1.42 ± 0.12
Switch (mean ± SD)	1.14 ± 0.18	1.19 ± 0.16	1.19 ± 0.17	1.14 ± 0.17	1.20 ± 0.15	1.19 ± 0.16
Proportion of correct answers
Non-switch (median and IQR)	0.97 (0.94–0.97)	0.97 (0.94–0.98)	0.97 (0.95–0.98)	0.98 (0.97–0.98)	0.98 (0.95–0.98)	0.97 (0.94–0.98)
Switch (median and IQR)	0.91 (0.85–0.95)	0.92 (0.87–0.95)	0.90 (0.88–0.94)	0.94 (0.90–0.97)	0.92 (0.91–0.94)	0.93 (0.89–0.95)
Sustained attention and information processing – PASAT
Reaction Speed
Level 1 (mean ± SD)	0.67 ± 0.07	0.68 ± 0.08	0.69 ± 0.08	0.67 ± 0.09	0.69 ± 0.07	0.67 ± 0.08
Level 2 (mean ± SD)	0.71 ± 0.06	0.73 ± 0.07	0.72 ± 0.06	0.72 ± 0.06	0.73 ± 0.06	0.74 ± 0.06
Level 3 (mean ± SD)	0.82 ± 0.05	0.81 ± 0.04	0.86 ± 0.17	0.82 ± 0.05	0.84 ± 0.06	0.83 ± 0.04
Level 4 (mean ± SD)	1.00 ± 0.04	1.04 ± 0.06	1.03 ± 0.05	1.02 ± 0.06	1.04 ± 0.06	1.04 ± 0.05
Number of correct answers
Level 1 (median and IQR)	54.50 (47.00–56.75)	53.00 (48.50–58.75)	55.00 (50.25–57.00)	56.00 (49.25–57.75)	55.00 (49.25–57.75)	55.00 (47.00–58.00)
Level 2 (median and IQR)	41.00 (33.25–51.00)	43.00 (31.50–53.50)	43.50 (40.00–54.00)	45.50 (32.75–48.00)	49.50 (34.50–43.75)	48.00 (35.25–55.50)
Level 3 (median and IQR)	25.50 (22.00–38.25)	27.00 (20.50–41.25)	31.00 (21.00–39.00)	27.00 (22.50–33.25)	29.00 (22.00–39.00)	29.00 (23.00–40.75)
Level 4 (median and IQR)	13.50 (10.00–17.00)	12.50 (7.25–17.75)	12.00 (9.25–18.75)	13.00 (7.50–17.00)	15.50 (10.25–17.00)	13.50 (10.50–16.75)

Fig. 7. Reaction speed in the number letter task (NLT) for non-switch trials (left) and switch trials (right). T1 = first measurement; T2 = second measurement; T3 = third measurement.

Table 4. Summary of significant results. ^a = partial Eta squared; ^b = Wilcoxon’s r; ^c = Kendall’s W; no significant results were observed in subjective sleepiness and negative affect (PANAS) ratings, working memory (2-back task) and vigilance (PVT). PANAS = positive and negative affect Schedule; NLT = number letter Task; PASAT = paced auditory serial addition task.

Measure	Significant Result	P-value	Effect size
Positive Affect (PANAS)	Main effect of measurement time	.004	0.336^a
Task Switching (NLT) - Reaction Speed	Main effect of measurement time in non-switch trials	<.001	0.354^a
	Main effect of measurement time in switch trials	<.001	0.417^a
Task Switching (NLT) - Proportion of correct answers	Increased proportion of correct answers at T1 under Personalized Lighting	.004	0.608^b
Sustained Attention (PASAT) - Reaction Speed	Main effect of measurement time in level 2	.016	0.178^a
Sustained Attention (PASAT) - Number of correct answers	Main effect of measurement time in level 2 in the control condition	.001	0.301^c

Table 5. Descriptive statistics on heart rate (HR) and pNN50. Pre = measurement before light exposure; post = measurement after light exposure; T1 = first measurement; T2 = second measurement; T3 = third measurement. PVT = psychomotor vigilance Task; NLT = number letter Task; PASAT = paced auditory serial addition task.

		HR		pNN50
		Control Condition	Personalized Lighting	Control Condition	Personalized Lighting
2-back	Pre	81.07 ± 12.46	82.66 ± 13.45	18.63 ± 16.79	15.75 ± 14.18
	Post	72.66 ± 9.53	72.22 ± 8.48	31.13 ± 15.80	33.37 ± 14.52
PVT	T1	77.48 ± 11.07	78.20 ± 10.17	25.30 ± 16.55	24.68 ± 14.57
	T2	74.54 ± 9.58	74.86 ± 9.82	28.09 ± 16.43	29.29 ± 14.45
	T3	71.67 ± 9.76	73.45 ± 10.09	32.72 ± 15.25	31.53 ± 13.18
NLT	T1	78.10 ± 11.33	79.61 ± 11.37	22.34 ± 19.73	21.26 ± 15.47
	T2	75.34 ± 10.86	74.61 ± 9.89	25.99 ± 19.66	28.06 ± 17.53
	T3	72.91 ± 11.53	72.74 ± 10.25	29.72 ± 21.96	32.03 ± 18.26
PASAT	T1	78.14 ± 11.21	79.01 ± 11.02	20.86 ± 18.72	21.62 ± 14.05
	T2	74.86 ± 11.42	74.47 ± 10.26	27.52 ± 19.35	28.98 ± 17.31
	T3	73.52 ± 11.62	72.78 ± 10.68	29.74 ± 19.50	31.33 ± 16.97
Breaks	B1	75.37 ± 10.40	75.24 ± 9.97	26.89 ± 16.61	29.35 ± 17.05
	B2	71.29 ± 9.96	71.47 ± 9.25	33.59 ± 17.97	35.35 16.85

Table 6. ANOVA test statistics including post-hoc tests for the main effect of measurement time on heart rate (HR) and pNN50. T1 = first measurement; T2 = second measurement; T3 = third measurement. Only two measurements exist for the 2-back and breaks, no post-hoc tests were calculated for these data. ‘negative‘ indicates a decrease of heart rate, “positive” indicates an increase in pNN50.

Parameter	Period	P	F	df	ηp^2	T1 - T2	T2 - T3	T1 - T3	Change
HR	2-back	<.001	35.362	1, 21	0.627	n.a.	n.a.	n.a.	Negative
	PVT	<.001	20.320	1.375, 28.874	0.492	.001	.014	<.001	Negative
	NLT	<.001	26.535	1.322, 27.756	0.558	<.001	.014	<.001	Negative
	PASAT	<.001	34.810	1.509, 31.688	0.624	<.001	.029	<.001	Negative
	Breaks	<.001	43.832	1, 21	0.676	n.a.	n.a.	n.a.	Negative
pNN50	2-back	<.001	42.150	1, 21	0.667	n.a.	n.a.	n.a.	Positive
	PVT	.003	6.495	2, 42	0.236	.137	.137	.002	Positive
	NLT	<.001	12.495	1.337, 28.074	0.373	.013	.040	<.001	Positive
	PASAT	<.001	18.468	1.337, 28.082	0.468	<.001	.160	<.001	Positive
	Breaks	<.001	25.883	1, 21	0.552	n.a.	n.a.	n.a.	Positive