## 4 Discussion
This second step is fundamental, as, for example, assessing the sustainability of a PLE involves careful consideration of technical, environmental, and social factors [121], which often require expertise in specific domains [38]. While citizens may offer subjective impressions, relying solely on such assessments can lead to inaccuracies and overlook critical aspects of sustainability. To ensure a more comprehensive evaluation and avoid inefficient solutions, qualified professionals must establish clear criteria for designing PLEs that effectively connect citizens with technical requirements. In addition, it is crucial to determine the significance and relative weight of each attribute of PLE during product development. By doing so, the impact of any potential improvements on customer satisfaction can be accurately measured. To accomplish this, an approach has been developed to assess the connections between the evaluations of each semantic axis and the global evaluation of the different PLEs. This study's results provide significant practical contributions. First, a series of concepts were defined that captured local residents' perceptions', in their own words, of local urban luminous environments. Five axes, which explained 75.13% of the variance (Table 4), were identified: _Expressive-interesting; Innovative-efficient; Defined-sufficient; Formal-uniform_ and _Glarging_. These axes describe the conceptual structure that local residents employ to differentiate the luminous environments of their urban areas. Comparing the results of this study with other works is challenging because few studies have been undertaken into luminous environments in urban areas in the framework of KE [51]. The application of KE in urban environments has focused mainly on the design of outdoor lighting appliances [95; 122]. Moreover, in general, most studies on PLE have evaluated one or two variables of light [73; 101; 102], frequently in laboratory conditions [103; 104], but scarcely the overall perceptions that luminous environments evoke, simultaneously examining the effects of all relevant variables. Nevertheless, it is worth contrasting some of the findings with other research. The axis _Expressive-interesting_ in this study is identified as the capacity of the PLE to create expressive-interesting sensations. Other studies have also employed this attribute in a comparable manner, utilising terms such as \"fascination\", \"entertainment\" [51], \"stimulating\" [81], and \"interesting\" [123]. Many of the adjectives that constitute this axis (Table 4) were used by [PERSON] et al. [124], with the term \"evaluative\". The axis _Innovative-efficient_ represents the union of the adjectives \"innovative, up-to-date, contemporary\", \"reflecting\", and \"efficient\". It is noteworthy that, in this case, in the semantic space of the local residents, these concepts were linked. In fact, many studies have connected these concepts [35; 125]. This is a significant contribution, because if lighting is to be perceived by citizens as efficient, it must give the impression of being innovative. The _Defined-sufficient_ axis represents the combination of the adjectives \"defined\" and \"sufficient\". [PERSON] et al. [79] also employed this concept under the adjective \"distinct\". The axis _Formal-uniform_ is formed by the union of the adjectives \"formal\", \"uniform\" and \"functional\". [PERSON] et al. [79] placed this concept within the category \"spatial modifiers\". These affective impressions can also be associated with other works that used the adjectives/terms \"uniform\" [81], \"uniformity\" [126], and the expression \"complexity\" used by [PERSON] and [PERSON] (1998). _Glarging_ is associated with the concepts \"glaring\" and \"resplendent\". This factor describes adjectives analysed in other studies, such as \"dazzling\" [127] and \"brilliant\" [76]. It is worth emphasising that local residents perceive this concept as an independent factor, as do experts.