## 3 Results
Although the circadian effects of light from displays vary drastically based on the computer tasks undertaken, their impact generally outweighs the impact of electric light when users sit at a desk and use computers. In certain circumstances, when typical tasks were performed in offices, light from computer screens even had a larger effect than daylight. For instance, on a sunny day, when an occupant sat with their back to the window, the melanopic irradiance at the eye position from daylight alone was 0.178 W/m\({}^{2}\) (_CS_ = 0.224), while the melanopic irradiance from the screen light was as high as 0.204 W/m\({}^{2}\) (_CS_ = 0.257). For the same display, the average melanopic irradiance at the eye position when users performed typical office tasks was 0.193 W/m\({}^{2}\), which was, on average, 2.7 times greater than when black-background software was used and 3.7 times greater than when a video was viewed. Figure 2 shows the distribution of _CS_ and melanopic irradiance values at a typical eye position caused by the light from different computer displays, when different tasks were performed on the computers. It is clear that, even across a wide range of products, the display light generally has a strong impact when typical office tasks, such as word processing, reading and writing emails, are undertaken. This result raises concerns about the possible negative circadian effects on office workers caused by light from screens. [PERSON] and colleagues suggested that self-luminous displays may be the primary cause of excessive light exposure during the night [30]. This study provides empirical data to support this supposition. Exposure to bright light at inappropriate times can lead to circadian disruption, which is associated with poor sleep quality, negative mood, and other health risks, such as diabetes, obesity, cardiovascular disease, and cancer [30]. Additionally, the phase of the circadian pacemaker can be delayed by exposure to light within a few hours before the midpoint of the melatonin secretion episode [35]. Office workers who regularly work late may experience these issues because of the light from their computer screens. This study only suggests the possibility of a negative influence on office workers' circadian rhythms based on the measured data and calculation results. Future studies are needed to investigate the circadian impact more directly by analysing salivary/blood melatonin levels and tracking office workers' sleep quality. Figure 1: The \(\alpha\)-opic irradiance and circadian stimulus (_CS_) for each of the three main sources of light in offices in commercial buildings. The red horizontal lines that divide the boxes into two parts mark the median (middle quartile). The boxes represent the inter-quartile range (the middle 50%) and the upper and lower whiskers show the highest and lowest non-outliers. The red crosses outside the boxes show the outliers. To further understand the circadian effects of electric lighting, light from a commercially available tuneable white lighting system, which mixes warm-white and cool-white LEDs, was further analysed. The spectral power distributions of three test lighting conditions (2762 K, 3968 K, 6253 K) are shown in Figure 3. In a windowless meeting room with constant illuminance, the melanopic irradiance at a modified eye position (simulating reading documents on a desk surface) was 0.133 W/m\({}^{2}\), 0.198 W/m\({}^{2}\) and 0.277 W/m\({}^{2}\), when the room was illuminated by 2762 K, 3968 K, 6253 K light and the illuminance kept approximately consistent (232 k, 228 k, 238 k, respectively). However, the _CS_ values calculated were 0.242, 0.194 and 0.310, respectively, which indicates a greater circadian impact from the 2762 K light than the 3968 K light. This inconsistency in the results between the CIE method and [PERSON]'s model is caused by the differences between and limitations of both methods discussed above. Further research needs to be conducted to develop a validated and universally accepted method for quantifying the circadian effects of light.