Rafael Lazar
PhD student, Psychologist
"Wie beeinflusst Licht die menschliche Physiologie, psychische Gesundheit und Leistung?" Ich interessiere mich besonders für die spektrale Zusammensetzung von Licht und wie es genutzt werden kann, um Schlaf, Leistung und Wohlbefinden zu verbessern, damit wir einen gesunden, nachhaltigen Lebensstil in unserer postmodernen Welt führen können.
Publications
2025
Lazar, R.; Fazlali, F.; Dourte, M.; Epple, C.; Stefani, O.; Spitschan, M.; Cajochen, C.
Afternoon to early evening bright light exposure reduces later melatonin production in adolescents Journal Article
In: npj Biol Timing Sleep, vol. 2, no. 25, 2025.
@article{nokey,
title = {Afternoon to early evening bright light exposure reduces later melatonin production in adolescents},
author = {R. Lazar and F. Fazlali and M. Dourte and C. Epple and O. Stefani and M. Spitschan and C. Cajochen},
url = {https://doi.org/10.1038/s44323-025-00040-6},
doi = {10.1038/s44323-025-00040-6},
year = {2025},
date = {2025-06-30},
urldate = {2025-06-30},
journal = {npj Biol Timing Sleep},
volume = {2},
number = {25},
abstract = {Whether light exposure during the day reduces non-visual light effects later in the evening has not been studied in adolescents. We investigate whether afternoon-early evening (AEE) light interventions (130 lx, 2500 lx, 4.5 h, compared to 6.5 lx illuminance) would increase melatonin levels during later evening light exposure (130 lx) in a counterbalanced crossover study with 22 adolescents (14-17 years, 11 female). Contrary to our hypothesis, evening melatonin levels decreased after AEE bright light exposure, while sleepiness and vigilance were unaffected, and skin temperature showed no clear changes. The AEE light had acute alerting effects and bright light exposure in the 32 h before laboratory entry was associated with higher evening melatonin and sleepiness. These findings suggest that bright AEE light increases alertness but may delay melatonin production by interfering with circadian rhythms. The study highlights the complex effects of light timing and its implications for managing adolescents’ light exposure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Whether light exposure during the day reduces non-visual light effects later in the evening has not been studied in adolescents. We investigate whether afternoon-early evening (AEE) light interventions (130 lx, 2500 lx, 4.5 h, compared to 6.5 lx illuminance) would increase melatonin levels during later evening light exposure (130 lx) in a counterbalanced crossover study with 22 adolescents (14-17 years, 11 female). Contrary to our hypothesis, evening melatonin levels decreased after AEE bright light exposure, while sleepiness and vigilance were unaffected, and skin temperature showed no clear changes. The AEE light had acute alerting effects and bright light exposure in the 32 h before laboratory entry was associated with higher evening melatonin and sleepiness. These findings suggest that bright AEE light increases alertness but may delay melatonin production by interfering with circadian rhythms. The study highlights the complex effects of light timing and its implications for managing adolescents’ light exposure.
2024
Lazar, R.; Degen, J.; Fiechter, A-S.; Monticelli, A.; Spitschan, M.
Regulation of pupil size in natural vision across the human lifespan Journal Article
In: R. Soc. Open Sci, vol. 11, pp. 191613, 2024.
@article{nokey,
title = {Regulation of pupil size in natural vision across the human lifespan},
author = {R. Lazar and J. Degen and A-S. Fiechter and A. Monticelli and M. Spitschan },
doi = {doi.org/10.1098/rsos.191613},
year = {2024},
date = {2024-02-27},
urldate = {2024-02-27},
journal = {R. Soc. Open Sci},
volume = {11},
pages = {191613},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2023
Siraji, Mushfiqul Anwar; Lazar, R.; van Duijnhoven, Juliëtte; Schlangen, Luc J M; Haque, Shamsul; Kalavally, Vineetha; Vetter, Céline; Glickman, Gena L; Smolders, Karin C H J; Spitschan, Manuel
An inventory of human light exposure behaviour Journal Article
In: Sci Rep, vol. 13, no. 1, pp. 22151, 2023, ISSN: 2045-2322.
@article{pmid38092767,
title = {An inventory of human light exposure behaviour},
author = {Mushfiqul Anwar Siraji and R. Lazar and Juliëtte van Duijnhoven and Luc J M Schlangen and Shamsul Haque and Vineetha Kalavally and Céline Vetter and Gena L Glickman and Karin C H J Smolders and Manuel Spitschan },
doi = {10.1038/s41598-023-48241-y},
issn = {2045-2322},
year = {2023},
date = {2023-12-01},
urldate = {2023-12-01},
journal = {Sci Rep},
volume = {13},
number = {1},
pages = {22151},
abstract = {Light exposure is an essential driver of health and well-being, and individual behaviours during rest and activity modulate physiologically relevant aspects of light exposure. Further understanding the behaviours that influence individual photic exposure patterns may provide insight into the volitional contributions to the physiological effects of light and guide behavioural points of intervention. Here, we present a novel, self-reported and psychometrically validated inventory to capture light exposure-related behaviour, the Light Exposure Behaviour Assessment (LEBA). An expert panel prepared the initial 48-item pool spanning different light exposure-related behaviours. Responses, consisting of rating the frequency of engaging in the per-item behaviour on a five-point Likert-type scale, were collected in an online survey yielding responses from a geographically unconstrained sample (690 completed responses, 74 countries, 28 time zones). The exploratory factor analysis (EFA) on an initial subsample (n = 428) rendered a five-factor solution with 25 items (wearing blue light filters, spending time outdoors, using a phone and smartwatch in bed, using light before bedtime, using light in the morning and during daytime). In a confirmatory factor analysis (CFA) performed on an independent subset of participants (n = 262), we removed two additional items to attain the best fit for the five-factor solution (CFI = 0.95, TLI = 0.95, RMSEA = 0.06). The internal consistency reliability coefficient for the total instrument yielded McDonald's Omega = 0.68. Measurement model invariance analysis between native and non-native English speakers showed our model attained the highest level of invariance (residual invariance CFI = 0.95, TLI = 0.95, RMSEA = 0.05). Lastly, a short form of the LEBA (n = 18 items) was developed using Item Response Theory on the complete sample (n = 690). The psychometric properties of the LEBA indicate the usability for measuring light exposure-related behaviours. The instrument may offer a scalable solution to characterise behaviours that influence individual photic exposure patterns in remote samples. The LEBA inventory is available under the open-access CC-BY license. Instrument webpage: https://leba-instrument.org/ GitHub repository containing this manuscript: https://github.com/leba-instrument/leba-manuscript .},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Light exposure is an essential driver of health and well-being, and individual behaviours during rest and activity modulate physiologically relevant aspects of light exposure. Further understanding the behaviours that influence individual photic exposure patterns may provide insight into the volitional contributions to the physiological effects of light and guide behavioural points of intervention. Here, we present a novel, self-reported and psychometrically validated inventory to capture light exposure-related behaviour, the Light Exposure Behaviour Assessment (LEBA). An expert panel prepared the initial 48-item pool spanning different light exposure-related behaviours. Responses, consisting of rating the frequency of engaging in the per-item behaviour on a five-point Likert-type scale, were collected in an online survey yielding responses from a geographically unconstrained sample (690 completed responses, 74 countries, 28 time zones). The exploratory factor analysis (EFA) on an initial subsample (n = 428) rendered a five-factor solution with 25 items (wearing blue light filters, spending time outdoors, using a phone and smartwatch in bed, using light before bedtime, using light in the morning and during daytime). In a confirmatory factor analysis (CFA) performed on an independent subset of participants (n = 262), we removed two additional items to attain the best fit for the five-factor solution (CFI = 0.95, TLI = 0.95, RMSEA = 0.06). The internal consistency reliability coefficient for the total instrument yielded McDonald's Omega = 0.68. Measurement model invariance analysis between native and non-native English speakers showed our model attained the highest level of invariance (residual invariance CFI = 0.95, TLI = 0.95, RMSEA = 0.05). Lastly, a short form of the LEBA (n = 18 items) was developed using Item Response Theory on the complete sample (n = 690). The psychometric properties of the LEBA indicate the usability for measuring light exposure-related behaviours. The instrument may offer a scalable solution to characterise behaviours that influence individual photic exposure patterns in remote samples. The LEBA inventory is available under the open-access CC-BY license. Instrument webpage: https://leba-instrument.org/ GitHub repository containing this manuscript: https://github.com/leba-instrument/leba-manuscript .
Stampfli, J. R.; Schrader, B.; di Battista, C.; Häfliger, R.; Schälli, O.; Wichmann, G.; Zumbühl, C.; Blattner, P.; Cajochen, C.; Lazar, R.; Spitschan, M.
The Light-Dosimeter: A new device to help advance research on the non-visual responses to light Journal Article
In: Lighting Research & Technology, 2023.
@article{nokey,
title = {The Light-Dosimeter: A new device to help advance research on the non-visual responses to light},
author = {J.R. Stampfli and B. Schrader and C. di Battista and R. Häfliger and O. Schälli and G. Wichmann and C. Zumbühl and P. Blattner and C. Cajochen and R. Lazar and M. Spitschan},
url = {https://journals.sagepub.com/doi/full/10.1177/14771535221147140},
doi = {https://doi.org/10.1177/14771535221147140},
year = {2023},
date = {2023-02-13},
urldate = {2023-02-13},
journal = {Lighting Research & Technology},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2022
Lazar, R.
Light flash therapy in the wild Journal Article
In: Nature Reviews Psychology, 2022, ISSN: 2731-0574.
@article{Lazar.2022,
title = {Light flash therapy in the wild},
author = {R. Lazar},
url = {https://rdcu.be/cQH7W},
doi = {10.1038/s44159-022-00084-6},
issn = {2731-0574},
year = {2022},
date = {2022-01-01},
journal = {Nature Reviews Psychology},
abstract = {In this Journal Club, Rafael Lazar describes a randomized field trial that tested whether light flash therapy improves the duration and timing of sleep in adolescents.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this Journal Club, Rafael Lazar describes a randomized field trial that tested whether light flash therapy improves the duration and timing of sleep in adolescents.
2019
Spitschan, M.; Lazar, R.; Yetik, E.; Cajochen, C.
No evidence for an S cone contribution to acute neuroendocrine and alerting responses to light Journal Article
In: Current Biology, 2019.
@article{Spitschan2019d,
title = {No evidence for an S cone contribution to acute neuroendocrine and alerting responses to light},
author = {M. Spitschan and R. Lazar and E. Yetik and C. Cajochen },
url = {https://www.cell.com/current-biology/fulltext/S0960-9822(19)31501-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982219315015%3Fshowall%3Dtrue},
doi = {10.1016/j.cub.2019.11.031},
year = {2019},
date = {2019-12-16},
journal = {Current Biology},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Spitschan, M.; Lazar, R.; Cajochen, C.
Visual and non-visual properties of filters manipulating short-wavelength light Journal Article
In: Ophthalmic Physiol Opt, 2019.
@article{Spitschan2019f,
title = {Visual and non-visual properties of filters manipulating short-wavelength light},
author = {M. Spitschan and R. Lazar and C. Cajochen},
url = {http://www.chronobiology.ch/wp-content/uploads/2020/01/Spitschan_et_al-2019-Ophthalmic_and_Physiological_Optics-1.pdf},
doi = {10.1111/opo.12648},
year = {2019},
date = {2019-11-01},
journal = {Ophthalmic Physiol Opt},
keywords = {},
pubstate = {published},
tppubtype = {article}
}