Influence Of Uniformity And Spectral Power Distribution Of LED On Discomfort Glare

Nowadays, light-emitting diode (LED) has been widely used due to its higher efficacy, longer life and lower-environmental pollution comparing with the conventional sources such as incandescent, fluorescent lamps. Meanwhile, there are issues concerning the lighting qualities of LED. A major issue concerning LED lighting applications is discomfort glare, which is the focus of the present study.Although there are some models predicting discomfort glare, they are mainly used to predict glare for large size and uniform white sources. They cannot work well with LEDs. Firstly, LED lights are generally non-uniform because of its small size and high intensity, even with the inclusion of lenses or diffusers. Secondly, LED sources can have variety of spectral power distribution (SPD), which have different colour appearance, colour temperature, colour rendering property. Many researchers have found that the above two properties (uniformity and SPD) could have a large impact on glare perception, while most existing glare models do not take them into consideration.The goals of the present study are a) to collect experimental data of glare perception under different parameters including non-uniformity and various SPDs of LED sources, b) to establish new definition of luminance or brightness to consider the effect of uniformity and SPD on glare perception, and c) to develop new models based the new definition of luminance or brightness.All the goals have been successfully achieved by conducting two experiments. For Experiment 1, the discomfort glare caused by LED luminaires having different uniformities was conducted. Four types of LED luminaires (raw LED chips, the LED covered by lens, the LED covered by a diffuser and raw LED with different luminance distributions. Observers scaled glare using a seven-categorical scale. The results showed that the UGR based on average luminance of glare source cannot predict glare results from all four types of sources consistently. Different non-uniform luminaires produce more glare perception than those of uniform ones. Furthermore, Unified Glare Rating (UGR) model was tested and performed badly. Hence, a modified model was proposed to estimate different degrees of uniformity, which is called UGRUNI.In addition, another glare model, QUGRUNI, was proposed based on a colour appearance model (see later).Experiment 2 was conducted to study discomfort glare caused by LEDs having different SPDs. It included both Coloured LEDs and white lights produced by various colored LEDs. The results showed that the UGR based on average luminance cannot predict all glare sources consistently. Coloured LEDs induced more discomfort glare than white lights with different CCTs. Blue LEDs led to the highest glare perception, especially for those having shorter peak wavelength. For developing new glare models, different visual sensitivity functions in the blue end of spectrum were integrated with V(λ) function to obtain a new luminance quantity. This model, named mUGRSPD was used, to replace the average luminance in UGR, to give accurate prediction to the visual results. Finally, a colour appearance model for unrelated lights was modified to accurately predict perceived brightness by taking into account the Helmholtz-Kohlrausch (H-K) effect. This model is named QUGRSPD.Both glare models markedly outperformed UGR.Finally, two generic glare models, named mUGR and QUGR, considering both uniformity and SPD were tested using an independent dataset. It showed that the new ones had similar performance and both performed much better than UGR. The mUGR is similar to the traditional UGR since they are both empirical formulations. While the QUGR is based on colour appearance model. It builds a bridge between glare evaluation and human visual principles for the first time. Therefore, it is promising to be applied in evaluation of LED lighting quality in the future.