LED由於兼具壽命長與低耗能等特性，符合現今重視節省能源的時代訴求，在光電產業佔有重要地位。而使用的範圍，也從辦公室的室內照明逐漸移向戶外，包含停車場以及夜間道路照明都是其應用範圍。當利用於夜間道路照明時，由於照明環境屬於明視覺與暗視覺間的中介視覺，對人眼最敏感的波長位於555 nm與507 nm之間，此波長屬於綠光波長，因此在原本的白光LED中混入綠光晶片，將有機會用節能的方式提供給使用者相同亮度感受的照明環境。本研究以積分球量測四種不同白綠混光比例的LED，並與全白的LED比較相同耗能下的中介視覺輝度與發光效率，同時以心理物理學實驗，用問卷的方式進行主觀視覺接受度的評估。
量測結果顯示，不論從中介視覺輝度或是發光效率來比較，不同白綠混光比例的LED在10-20 mA的低驅動電流時，節能效果皆是隨S/P-ratio(暗明視覺比例)升高而提高，而在高電流350 mA時則是若S/P-ratio低於4W3G(四個白光與三個綠光晶片的混光LED)的1.952時，與純粹白光LED晶片(5W)在發光效率的比較上即不再有節能效果。在視覺接受度實驗中，5W4G與4W2G與5W有相近的接受度，而在色度座標上較偏綠色的4W3G與4W4G明顯的較不被受試者所接受。本研究顯示提高S/P-ratio可幫助達到節能的目標，而節能且具接受度的白綠混光LED是可行的應用方向。

Light-emitting diodes (LEDs) occupy an important portion in the optoelectronics industry due to their good characteristics, such as long life time and low energy consumption, meeting the worldwide demands for energy saving. The range of LED usage has gradually moved from indoor lighting to outdoor lighting. The applications include parking lot lighting and street lighting at night. Human eyes in these lighting environments are under mesopic vision, which is between scotopic and photopic visions and is most sensitive to green light with wavelengths between 507 and 555 nm. For this reason, adding green content to white light LEDs shall have the opportunity to provide illumination with less energy but the same brightness to users.
In this study, five different proportions of green to white LED chips are packaged, including 5W4G (5 white and 4 green chips), 4W4G, 4W3G, 4W2G, and 5W. These LEDs are measured by an integrating sphere. The spectra and energy consumptions are used to compute the energy saving ratios compared to the case of 5W in terms of mesopic luminance and luminous efficacy. Besides, psychophysical experiments are conducted to assess the visual acceptability and clarity of these LEDs by questionnaires.
The measurement results show that for different proportions of green to white LEDs at low driving currents (10-20 mA), the energy saving ratio is better when the LED has a higher S/P-ratio (scotopic and photopic ratio). This is true both in terms of mesopic luminance and luminous efficacy. However, at a higher driving current of 350 mA, when the S/P-ratio is lower than 1.952 (the case of 4W3G), the LED no longer has the energy saving property in luminous efficacy compared to the case of 5W. In psychophysical experiments, the cases 5W4G, 4W2G and 5W have approximate visual acceptability and clarity, and are better choices than the cases 4W4G and 4W3G, whose chromaticity coordinates are closer to the saturated green color. This study validates that raising the S/P-ratio of LEDs is beneficial for energy saving. Adding green chips into white light LEDs has the potential for energy efficient lighting with high visual acceptability and clarity.

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