Table 1.

Study outcome measures and corresponding questionnaires.

Variable	Assessment	Details
Primary Outcomes
Cancer-related fatigue	VAS-fatigue	1 item; 11-point Likert scale Total score: 0–10; higher scores indicate more fatigue. Time frame: this moment.
	MFI	20 items; 5-point Likert scale. Subscales: general fatigue, mental fatigue, physical fatigue, reduced motivation, reduced activity. Only general fatigue is used since psychometric validation of this scale indicated that this subscale is the most reliable [36]. Subscale score: 4–20; higher scores indicate more fatigue. Time frame: past few days.
Restrictions caused by fatigue	WSAS	5 items; value range between 0.00 and 8.00. Total score: 0–40; higher scores indicate higher levels of disability. Time frame: influence of fatigue on daily life.
Secondary Outcomes
Sleep quality	PSQI	19 items; 4-point Likert scale and open-ended questions. Subscales: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, daytime dysfunction. Total score: 0–21; subscale scores: 0–3; higher scores indicate more acute sleep disturbances. Time frame: past month.
Depression	CES-D	20 items; 4-point Likert scale. Total score: 0–60; higher scores indicate greater depressive symptoms. Time frame: past week.
Anxiety	STAI-6	6 items; 4-point Likert scale. Total score: 20–80; higher scores indicate increased anxiety. Time frame: this moment.
Quality of life	RAND-36	36 items; dichotomous and 3- to 6-point Likert scale. Scales: physical functioning, role limitations due to physical health, role limitations due to emotional problems, energy, emotional well-being, social functioning, pain, general health Scale scores: 0–100; higher scores indicates higher levels of functioning/well-being. Time frame: past 4 weeks.
Sleep	Wrist actigraphy	Device: MotionWatch8 (Camntech, Cambridgeshire, United Kingdom). Software to handle data: MotionWare (Camntech, Cambridgeshire, United Kingdom). Technical settings: epoch length 60 s, tri-axial mode. Location: non-dominant wrist. Time period: 10 days (Friday 18:00 h till Monday 12:00 h). Actigraphy log included: bedtime, attempted time to fall asleep, wake-up time, out-of-bed time, nap times, non-wear times. Derived sleep variables: sleep efficiency, mid sleep, and total bedtime. Derived sleep-wake rhythm variables: Interdaily stability (IS; an estimate of the 24-h sleep-wake rhythm) and intradaily variability (IV; an estimate of the stability of the sleep–wake rhythm) [44]. A measurements point was excluded from the sleep variables analyses when the actigraphy was worn for less than 4 nights and from the sleep–wake rhythm variables analyses when the actigraphy was worn for less than 72 consecutive hours. Scores: IS: 0–2; higher scores indicate a more fragmented rhythm; IV: 0–1; 1 indicates perfect synchronization.
Cortisol	Salivary cortisol	Saliva collection via a passive drool technique in a propylene vial at the participants’ home. Sample collection on five different time points during 24 consecutive hours: (1) at personal waking time, (2) 30 min after awakening, (3) 45 min after awakening, (4) at 16.00 o’clock, and (5) at bedtime. Saliva collection was on the Friday prior to light therapy (start day Monday) and the Friday after completion of light therapy (finish day was Thursday). After sample collection, saliva samples were stored in the refrigerator and mailed to the lab via post where the samples were stored in a freezer at a -80 °C until processing. Cortisol values (nmol/L) were determined using liquid chromatography tandem mass spectrometry. Method imprecisions were ≤13.9% and lower limits of quantitation were 0.5 nmol/L. Derived variables: cortisol awakening response, diurnal cortisol slope, area under the curve. For further details on the analytical method and performance characteristic, see Supplementary material 2.
Melatonin	Salivary melatonin	Subsample (n = 60). Collection of five additional saliva samples starting 5 h prior to bedtime followed by one sample every sequential hour. Collection and handling of samples was similar to the procedure described for cortisol. Method imprecisions were ≤11.9% and lower limits of quantitation were 0.01 nmol/L. Derived variables: Dim Light Melatonin Onset (DLMO) based on the hockey-stick method [47]. For further details on the analytical method and performance characteristic, see Supplementary material 2.

Note: shading in the table represents the distinction between variables. Abbreviations: CES-D, Center for Epidemiological Studies—depression scale; CWS, Cancer Worry Scale; FCS, Fatigue Catastrophizing Scale; MFI, Multidimensional Fatigue Inventory; nmol/L, nanomoles per liter; PSQI, Pittsburgh Sleep Quality Index; RAND-36, medical outcome studies short form; SES-28, self-efficacy scale 28; STAI-6, State-Trait Anxiety Inventory (6); VAS, visual analogue scale; WSAS, Work and Social Adjustment Scale.