###### Abstract  
The proliferation of electric and hybrid vehicles has made it possible for people to read and work in a stationary vehicle for extended periods. However, the current commonly used in-vehicle lighting design is still centered around driving and driving safety. Following recommendations from the literature, a neutral white color band (4000 K-5000 K) with 50-100 x at the vehicle table area is favored. Whether this lighting environment can meet the needs to enhance the reading performance in a modern vehicle was investigated in this presented study. Therefore, in total, 12 lighting settings were designed based on combinations of four illuminance levels (50 lx, 100 lx, 150 lx and 200 lx) and three correlated color temperatures (3000 K, 4000 K and 5000 K); we recruited 19 subjects (12 females, 7 males) and let study participants evaluate each condition based on electronic and paper reading. Next, subjective preferences, positive and negative emotions, feeling of fatigue and sustained attention were tested. We found that higher illuminance and higher CCT (Correlated Color Temperature) can significantly improve the performance of in-vehicle readers in most aspects following [PERSON]'s law (\(p<0.05\)). Among them, we recommend the combination of 150 lx and 4000 K as the light parameters for in-vehicle reading as a new development guideline. In addition, we also discovered the inconsistency of people's lighting preferences between in-vehicle spaces and conventional spaces. For indoor lighting, illuminance values up to 1000 lx are still favored. For an in-vehicle function, starting with 200 lx, the preference level and reading performance already declined. In comparison between electronic and paper reading, both were similarly evaluated. These results show that a neutral white light color should be chosen with a horizontal illuminance of maximal 150 lx for a reading light function independent of the reading device. Interdisciplinarily speaking, our findings can be applied in similar small spaces or transportation modes with gentle acceleration and deceleration such as small space hotel rooms, trains, airplanes or ships. in-vehicle lighting; light-mood relation; light-fatigue relation; light-attention relation; illuminance preferences; CCT preferences +
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considered uncomfortable or unsatisfactory [13; 14; 15; 16; 17; 18]. Preferences for lighting scenes improve as illumination increases from 1000 lx to 1800 lx [19]. Yet, recent studies on lighting in small spaces have opted for significant lower levels of horizontal illumination than those used in larger areas. For instance, research on capsule hotel lighting by [PERSON] et al. explored illumination levels of 150 lx and 300 lx [20], while [PERSON] et al. investigated a range from 20 lx to 250 lx in very small spaces, finding optimal comfort at 100 lx before it declined with increased brightness [21]. These variations in research parameters and findings highlight the complexity of adapting lighting studies from conventional to specialized small spaces [22; 23; 24; 25; 26; 27; 28; 29]. Small spaces, defined by their significantly reduced physical and psychological dimensions compared to standard environments, offer considerable advantages in space and cost savings [30; 31]. Existing research has shown that as vertical illuminance increases, the overall perception of spatial brightness in subway cabins is enhanced [32]. The interior of vehicles represents a quintessential example of such a small space environment. The evolution of vehicle lighting, marked by the shift to LED technology, has significantly enhanced in-vehicle lighting functions. Previously limited to basic tasks with white tungsten lamps, modern vehicles now offer advanced lighting and connectivity features. LED's energy efficiency and design flexibility, coupled with vehicle internet connectivity, have transformed vehicles into mobile offices and reading spaces, enabling activities like online reading and extended work sessions during travel.