dc.description.abstract | LED technology is changing with each passing day. LEDs have been widely used in lighting applications, including traffic signs. In order to improve the safety of night driving, more and more traffic signs have utilized LEDs. But these traffic signs need to be evaluated. Our previous studies have evaluated four custom-made LED highway traffic signs with different designs in three aspects, including the legibility, visual comfort and preferences. Each aspect was evaluated independently at the time. The current study uses the generalized estimating equations to calculate the marginal mean as the evaluation score for each sign’s messages when legibility, visual comfort and preferences across all signs are controlled.
The other study in this thesis is modifying the lens design with partial backward lighting in our previous studies to be used on LED traffic signs of dot matrix type. We designed a total of 11 lenses back then, and among them two lenses were more effective and applicable. The lens that we selected for the ergonomic experiment is based on a thin plastic sleeve with one end coated with 90 % highly reflective coating. The lens was designed to be fitted on bullet-shaped LEDs, but the LEDs used on the signs have silicone on the outer layer for waterproof and dustproof. So the lens is larger than the original design. In order to be durable, the lens material is changed from acrylic to polycarbonate. The influence of the above factors increases the illumination area of the backward light, and the intensity decreases. As a result, the power ratio of front-facing light to backward light is 10.38:1, which is still within the acceptable range although it is different from the original expectation.
The ergonomic experiments evaluate the legibility, visual comfort and preferences of each part of the traffic sign at the distance of 75 m and 30 m. The experimental data are estimated by the method of generalized estimation equations described in the previous paragraph. Then the pairwise comparisons on the mean evaluation scores are tested in three ways, including the data of Wan word, Li word and both of them. The results show that the lens with partial backward lighting has no benefit in improving the visual quality of LED traffic signs of the dot matrix type. Nevertheless, future experiments can still try some other lenses and tune the optical design to control the illumination area and intensity of backward lighting, in order to achieve better visual quality of LED traffic signs of dot matrix type.
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