## 4 Discussion  
The data collected in this study reveals that the effects of light on occupants' circadian rhythms are limited currently in residential buildings for home offices. It is relatively uncommon for professional designers to be involved in the planning of daylight and electric lighting in residential buildings, which may account for some of the difference. Because more people are working from home and spending increased time in home offices, increased attention on the quality and quantity of lighting in residential buildings is warranted. The result also confirms that daylight strongly influences occupants' circadian rhythms, which has been demonstrated in previous studies [7; 14; 15; 16; 17]. These results indicate that human-centric lighting systems that only consider the effects of electric light sources are unlikely to appropriately estimate the extent to which occupants' circadian systems are stimulated. The effects of electric light on human circadian rhythms were shown to be weaker than the light from displays and daylight in these field measurements. To most optimally support the circadian health of building occupants, advanced lighting systems should account for all sources of light incident upon people. The measurements reported here address [PERSON]'s concern about the lack of real-world data [26]. The results support [PERSON] and colleagues' conclusion that light-emitting devices do affect users' circadian rhythms [25]. However, rather than being overestimated, as suggested by [PERSON] [26], the effect of light from light-emitting devices is surprisingly large. It can even exceed the effect of overhead electric lighting. Future internet of things (IoT) systems are expected to connect window shading systems, air conditioning, electric light, and computers together. Such systems could control the window shades, adjusting the amount of daylight in the room to optimise the thermal environment, as well adjust the spectra of light emitted by the computer screens and electric lights, according to changes in daylight. Although it is common today for computers to adjust the luminance of screens automatically in response to ambient brightness, this capability was not primarily developed with the aim of minimising negative impacts on users' circadian rhythms. People who regularly work late can experience delayed sleep phases and poorer sleep quality. With connected IoT systems, when users perform computer tasks in which the circadian effect of the light from the display is high, the electric lighting could be reduced to minimize potential negative circadian impacts. Results from emerging research on spectral optimisation could be potentially adapted to optimise the circadian effect of light and minimise the energy consumed by lighting [36]. This study also reveals that conventional architectural lighting design practices and many current lighting standards do not yield the spatial distribution of light needed in interior spaces to influence circadian rhythms. The electric lighting systems that were measured here were conventional in design and predominantly provided light downward. Though the lighting industry is enthusiastic about human-centric lighting, the data show that, for most typical environments, electric lights' effects on circadian rhythms are limited. Simply replacing the traditional luminaires with spectrally-tuneable variants in retrofit projects may not effectively optimise the effect of lighting on circadian rhythms. The spatial distribution of light needs to be considered, possibly with amendments to lighting standards and regulations. Currently, some standards, such as the WELL Building Standard TM [37], take the vertical illuminance, converted to equivalent melanopic lux (_EML_), into account, but most indoor lighting standards only make recommendations regarding horizontal illuminance [38; 39; 40].