| dc.description.abstract | The purpose of this study was to evaluate visual comfort and task performance of LED desk lamp users when reading under different central illuminance levels, with various contrast ratios between the central and ambient illuminance, and at different test time. The experiment was implemented in two parts. The first part is the high-central-illuminance and low-contrast experiment. Thirty-six subjects participated in this study voluntarily, and their ages ranged from 18 to 25 years old. The independent variables were the central illuminance (1000, 1500, or 2000 lux), the contrast ratio between the central and ambient illuminance (1:0, 4:1, 3:1, or 2:1) and the test time (morning, afternoon, or night). The second part is the low-central-illuminance and high-contrast experiment. Forty-five subjects participated in this study voluntarily, and their ages ranged from 18 to 25. The independent variables were the central illuminance (100, 200, 500, 750, or 1000 lux), the contrast ratio (10:1, 5:1, or 2:1) and the test time (morning, afternoon, or night). The dependent variables were the subjective visual comfort rating and the correct ratio of word-labeling in both parts.
The results indicated that when reading with a LED desk lamp, the central illuminance must be at least 500 lux to achieve satisfactory visual comfort. A central illuminance level of 1000 lux is sufficient for reading, and thus there is no need to pursue much higher illuminance for LED desk lamps. In addition, it is important to have ambient lighting when using desk lamps. Based on the experimental results, the best contrast ratio between the central and ambient illuminance is 2:1. If energy saving is highly demanded, 4:1 or 5:1 are also appropriate choices. It is not necessary to establish individual illuminance suggestions for different time during the day, unless the task performance is extremely important. The correct ratio of word-labeling was not affected by the independent variables, but the number of labeled words was influenced by the central illuminance when the contrast was high. When the ambient was relatively dark, the central illuminance must be higher than 500 lux for good task performance. This result coincided with the outcome of the visual comfort experiment. According to the research results, comfortable lighting environments could only be realized when the central and ambient illuminance is appropriately collocated.
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