「環境效率」指的是，環境品質與環境負荷的比值。對室內空間的照明計畫而言，提升品質與降低負荷，是永續時代追求的目標。但若一昧的追求照明節能，而使得照明品質低落，或為了提升照明品質卻必須投入更多不必要的能源，以環境效率的觀點來看，皆是徒勞無功。目前為止國內外的照明研究，鮮少以環境效率的觀點來討論。本研究率先以環境效率觀點，導入可反映環境負荷多寡的「照明用電密度」因子做為照明的操縱變因之一。本研究探討「照明型式」、「色溫度」與「照明用電密度」共3因子所組成的8種照明環境下，工作者進行5種類共60分鐘的工作前、工作後及休息期間的正負向情緒變化，及工作績效差異。研究結果顯示，3000K的黃光與6500K的白光相比，3000K的黃光較能提升正向情緒，以及降低負向情緒。3000K的黃光若搭配間接照明，則效果更佳。大部分的情緒表現在用電密度8W/m2或16W/m^2都差不多。16W/m^2提升了一倍的環境負荷，卻維持相同的環境品質，環境效率只有8W/m^2的1/2。桌上照度大約在400lx～600lx左右，可以得到較佳的情緒表現，照度在300lx以下，或超過800lx時，都會對疲勞與舒適程度產生反效果。用電密度由8W/m^2提高至16W/m^2時，環境負荷增加了一倍，但工作績效最多僅提升了5～8%，環境效率幾乎減半。本研究發現，使環境效率最大化的照明計畫原則是使空間裡的桌上照度控制在400～600lx左右，並盡量降低照明用電密度。

＂Eco-efficiency＂ refers to the ratio of environmental quality and environmental load. This study controlled the factor ＂Lighting power density＂, which can reflect the amount of environmental load but rarely discussed. This study discussed office worker’s moods and task performance in eight lighting environments, which were the combination of two illumination types, two color temperatures and two lighting power densities. The findings showed that 3000K is more advantageous to moods than 6500K, particularly when 3000K combines indirect lightings. When lighting power density increased from 8 to 16W/m^2, most of the moods did not increase significantly, and the improvement of task performance was 5-8% at most. This means that eco-efficiency decreased to 1/2 at 16W/m^2 than 8W/m^2.As for illuminance level, people's moods were better when illuminance on a desk is between400 and 600lx. When illuminance on a desk is lower than 300lx or higher than 800lx, both ＂Fatigue＂ and ＂Amenity＂ become more disadvantageous.