In order to anticipate the predictable changes in the environment associated with the earth’s rotation, most organisms possess intrinsic biological clocks. To be useful, such clocks require a reliable signal of ‘time’ from the external world. In mammals, light provides the principle source of such information; conveyed to the suprachiasmatic nucleus circadian pacemaker (SCN) either directly from the retina or indirectly via other visual structures such as the thalamic intergeniculate leaflet (IGL). Nonetheless, while the basic pathways supplying sensory information to the clock are well understood, the sensory signals they convey or how these are processed within the circadian system are not. One established view is that circadian entrainment relies on measuring the total amount of environmental illumination. In line with that view, the dense bilateral retinal input to the SCN allows for the possibility that individual neurons could average signals from across the whole visual scene. Here I test this possibility by examining responses to monocular and binocular visual stimuli in the SCN of anaesthetised mice. In fact, these experiments reveal that SCN cells provide information about (at most) irradiance within just one visual hemisphere. As a result, overall light-evoked activity across the SCN is substantially greater when light is distributed evenly across the visual scene when the same amount of light is non-uniformly distributed. Surprisingly then, acute electrophysiological responses of the SCN population do not reflect the total amount of environmental illumination. Another untested suggestion has been that the circadian system might use changes in the spectral composition of light to estimate time of day. Hence, during ‘twilight’, there is a relative enrichment of shortwavelength light, which is detectable as a change in colour to the dichromatic visual system of most mammals. Here I used a ‘silent substitution’ approach to selectively manipulate mouse cone photoreception, revealing a subset of SCN neurons that exhibit spectrally-opponent (blue-yellow) visual responses and are capable of reliably tracking sun position across the day-night transition. I then confirm the importance of this colour discrimination mechanism for circadian entrainment by demonstrating a reliable change in mouse body temperature rhythms when exposed to simulated natural photoperiods with and without simultaneous changes in colour. This identification of chromatic influences on circadian entrainment then raises important new questions such as which SCN cell types process colour signals and do these properties originate in the retina or arise via input from other visual regions? Advances in mouse genetics now offer powerful ways to address these questions. Our original method for studying colour discrimination required transgenic mice with red-shifted cone sensitivity – presenting a barrier to applying this approach alongside other genetic tools. To circumvent this issue I validated a modified approach for manipulating wildtype cone photoreception. Using this approach alongside optogenetic cell-identification I then demonstrate that the thalamic inputs to the SCN are unlikely to provide a major source of chromatic information. To further probe IGL-contributions to SCN visual responses, I next used electrical microstimulation to show that the thalamus provides inhibitory input to both colour and brightness sensitive SCN cells. Using local pharmacological inhibition I then show that thalamic inputs supress specific features of the SCN light response originating with the contralateral retina, including colour discrimination. These data thus provide new insight into the ways that arousal signals reaching the visual thalamus could modulate sensory processing in the SCN. Together then, the work described in this thesis provides important new insight into sensory control of the circadian system and the underlying neural mechanisms.

Die Gestaltung der Beleuchtung und das farbliche Design an Wissensarbeitsplätzen ist durch viele technische und gestalterische Neuerungen ein aktuelles Thema arbeitswissenschaftlicher Forschung. LEDs, Tageslichtnachahmung und dynamisches Licht sind aktuelle Innovationen, die den Arbeitsalltag immer mehr durchdringen. Zum einen müssen nun diese Konzepte ergonomisch untersucht und gestaltet werden, um zu einer Erhöhung von Leistung, Sicherheit, Informationsfluss oder Wohlbefinden zu kommen. Andererseits sind die Anforderungen der Nutzer von Belang, da sich eine licht- und farbtechnische Gestaltung an diesen orientieren sollte. Aus diesem Grund wurde an der Professur Arbeitswissenschaft der TU Chemnitz eine empirische Studie zu Wissensarbeitsplätzen durchgeführt. Nutzer wurden mittels eines teilstandardisierten Fragebogens zu Ihren Anforderungen an Beleuchtung und Farbgestaltung am Arbeitsplatz und vergleichend in ihrer Wohnung befragt.

Syfte: Syftet med studien är att få en inblick i hur färgtemperaturen kan påverka personers trivsel i bostadsområden. Detta är för att få en förståelse om hur ljusets färgtemperatur påverkar personers trivsel, positiva eller negativa effekter och vilka skillnader som syns med det olika färgtemperaturerna. Metod: Två metoder användes i studien. Ett frågeformulär skapades med 8 självtagna bilder med tillhörande frågor. Efter att deltagarna svarat på enkäten, genomfördes intervjuer med fem deltagare som valdes ut genom hur det svarade på frågorna och fick utveckla sina svar. Resultat: Resultaten visar att det finns en skillnad mellan varmt och kallt ljus, i hur det påverkar trivseln. Hur det påverkar trivseln beror dock på vad deltagare anser själva är en trivsam belysning. Ur frågeformulär var det en stor variation av deltagare som kopplade låg färgtemperatur till komfort och hemlik atmosfär. Högre färgtemperaturer kopplades mer till trygghet och modernt ljus. Ur intervjuer visade resultatet att fler deltagare föredrar lägre färgtemperatur i bostadsområden, då det känns mer behagligt och mer passande. Färre antal föredrog högre färgtemperaturer och kopplade det till att det lyser upp mer av omgivningen och blev mer följsamt för ögat. Deltagare kopplade mycket till omgivningen då bilderna visade olika områden. Mycket hus, bilar, belysning ifrån hus och grönskan bidrog mycket till att deltagare valde bilderna och kopplade det till hus ljuset spred sig i omgivningen.  Konsekvenser: Studien ger kunskap om färgtemperaturens roll för utomhusbelysning och vikten av den. Detta gynnar boende och gående inom bostadsområden. Genom att veta vilken färgtemperatur som föredras, kan belysning projekteras och planerare kan skapa den belysning som befolkningen anser är nödvändig och trivs bäst med.  Begränsningar: Studien är begränsad till att undersöka endast färgtemperatur i bostadsområden. Intervjuer genomfördes på distans i digital plattform, med hänsyn till rådande situation av covid-19. / Purpose: The purpose of the study is to gain an insight into how colour temperature can affect people's well-being in residential areas. This is to gain an understanding of how the colour temperature of light can affect well-being, whether it affects positively or negatively, if there are differences and in what way it differs. Method: Two methods were used in the study. A questionnaire was created, with 8 self-taken pictures with additional questions. After the participants responded to the questionnaire, interviews were conducted with five participants who were choose by how they answered and were allowed to develop their answers. Findings: The question asked had a broad answer. The results show that there is a difference between low and high colour temperature, how it affects well-being. However, how it affects well-being depends on what the participants consider to be a pleasant lighting. From the questionnaire, there was a large variety of participants who linked low colour temperature to comfort and homely atmosphere. Higher colour temperatures were linked more to security and modern light. From interviews, the results showed that more participants prefer lower colour temperature in residential areas, as it feels more comfortable and more appropriate. Fewer numbers preferred higher colour temperatures and linked it to the fact that it lit up more of the surroundings and became more compliant to the eye. Participants connected a lot to the surroundings as the pictures showed different residential areas. The pictures included a lot of houses, cars, lighting from houses and greenery, which contributed a lot to participants choosing the pictures and linking it to how the light spread in the surroundings. Implications: Conducting a study entails knowledge within the role of colour temperature for outdoor lighting and the importance of having it. This benefits residents and pedestrians in residential areas, by knowing which colour temperature is preferred, lighting can be projected, and planners can create the lighting that the population considers necessary and are most comfortable with. Limitations: The study has mainly focused on the colour temperature in residential area. Interviews were conducted remotely on a digital platform, considering the prevailing situation of covid-19.