發光二極體做為室內照明光源對視網膜影響之大鼠研究

Abstract

照明是生活的基本需求，人工光源也由照亮空間的基本要求，延伸至人因工程所關注的健康與舒適考量。近來各界積極推動節能照明，發光二極體 (Light Emitting Diode, LED) 照明以環保節能的優勢深獲期許，其中室內照明以白光LED做為替代光源頗具潛力與代表性。而 LED屬固態發光 (Solid State Lighting, SSL) 的一種，是由半導體材料所製成的發光元件，不同材料與製程可發出不同的波長，視覺系統藉此感受到不同顏色的光。LED 的發光特性與光學表現適合應用於指示性的用途，當轉型發展成為一般照明，目前符合經濟效益且成為主流的白光LED，大多為藍色晶片搭配黃色螢光粉的 (phosphate-conversion, PC) 的型態，而其光譜有一大區間落於400 nm – 550 nm，屬於視網膜藍光危害區，且其中尖銳的藍光波峰所呈現的單點強度，可能對視網膜產生傷害而未被人眼察覺，長期低劑量的暴露也可能對黃斑部產生累積性的負面效應而不自覺。因此LED 照明如何呈現最適合生理機轉的光學表現，有待醫學及公衛體系的專業研究並加以定義。 本研究之目的在探討以白光LED為室內照明光源時，其所含不同波長光線對於視網膜的潛在影響。有別於前人研究多以短時間（數秒至數天）的方式進行，本研究針對白光LED作為室內照明光源之波長與頻譜分佈進行長期低暴露分析，透過大鼠動物實驗，以視網膜電波圖 (electroretinogram , ERG) 檢查視網膜功能上所受的衝擊，同時以多種組織切片觀察感光細胞形貌上的改變，以及透過生化分析觀察細胞受到氧化壓力而引發的凋亡和壞死狀況，探討視網膜光傷害的機轉，研析白光LED 照明對使用者視網膜生理結構的影響。為達成此研究目的，整體研究架構以二階段實驗方式進行。 第一階段以藍光 LED (460 nm) 以及全頻譜的白光 LED (CCT 6500) 搭配相對應的螢光燈管 (CFL, CCT 6500) 和黃光 (CFL, CCT 2700) 對大鼠進行照光暴露實驗，以證實在參數相同的暴露環境中，LED 比 CFL 更容易誘發視網膜的光傷害。接著第二段實驗以三種不同波段的LED 光源，包括藍光（ 460 nm）、綠光 (530 nm)及紅光 (620 nm) 進行比對，透過更深入的生化分析工具，觀察 LED 所誘發的視網膜光傷害是否存在波長的劑量效應關係，以及其傷害機轉。實驗結果證實大鼠視網膜感光細胞在不同光源的暴露下產生的光化學危害 (photochemical injury) ，細胞結構變化是由氧化壓力所引發，且呈現波長的劑量效應關係。相同暴露參數下，波長越短造成的傷害越強，因而推論在大鼠實驗中，做為室內照明的白光LED光源中，藍光對視網膜的危害貢獻最多。 以環境衛生的角度，本研究結果提醒以LED 做為室內照明時，必須特別留意頻譜中藍光的比重分佈。同時也提供予相關產業於產品研發時挹注健康的考量因子，並呼籲使用者注意暴露風險與防範措施 。然而以風險評估的觀點而言，此動物實驗結果並無法直接定義人類的使用風險，尚須經過適當的評估或甚至進一步的人體暴露分析才能得到具體結論，未來應有更多學者延續此主題的研究。

The rapid development of white light-emitting diode (LED) lighting has raised serious retinal hazard concerns. LED delivers higher levels of blue light to the retina compared to conventional domestic light sources. However, the majority of the published retinal blue light injury studies are either in anesthetized animals or in vitro with high exposure intensity for acute injury assessment. The significance of the blue component in LED lighting contributing to the injury needs further study in a free-running animal model with chronic exposure setting. This study intends to assess the potential adverse effects from exposure to the domestic LED lights with different wavelengths. Two sets of LED-induced retinal neuronal cell damage in the Sprague-Dawley rat models through functional, histological, and biochemical measurements were completed. In the first part of study, blue LED (460 nm) and full-spectrum white LED (CCT 6500) coupled with matching compact fluorescent lamps (CFL) were used for exposure treatments. The results suggested that the LED white light has a higher chance to induce retinal photochemical injury (RPI) than does the conventional CFL white light. The results raise questions related to adverse effects on the retina from chronic LED light exposure compared to current lamp sources that have less blue light. To further assess the risk, LED induced RPI with wavelength dependency and its mechanism were focused on the second part of study. Although there has been a wealth of studies describing the RPI associated with wavelength dependency previously, the experimental settings were focused on high intensity light exposure over a short period of time (a few seconds to 3 days) for acute or subacute toxicity assessments. The tested animals were anesthetized or forced to stare into the lights in most of the cases, and the light sources varied due to contemporary technology availability. Thus, in the second part of study, blue (460 nm), green (530 nm), and red (620 nm) LEDs were investigated to measure how specific bands were responsible for retinal phototoxic effects under the same irradiance level at 102 μW/cm2. Both functional and histopathological results indicated blue light-induced RPI. The oxidative stress and iron-related molecular markers suggested that blue LED exposure increased retinal toxicity compared with longer wavelength LEDs. Biochemical assays on lipid, protein, and DNA also showed higher oxidative expressions after blue LED exposure. LED light-induced retinal injury could be due to oxidative stress through iron overload. Several biomarkers confirmed the greater risk of LED blue-light exposure in awake, task-oriented rod-dominant animals.   Based on the study results, it is concluded that LED light exposure may induce RPI through oxidative stress with a wavelength-dependent effect. More importantly, the long-term effects of exposure to low doses of domestic lighting may lead to serious retinal degenerative diseases. Several functional, morphological, and biochemical measurements were applied to characterize the exposure results associated with this injury. The wavelength-dependent effect should be considered carefully when switching to LED domestic lighting applications. However, the exact mechanism underlying these effects will be the subject of ongoing investigation with more analytical methods. The interpretation from the animal study to human applications should also be carefully considered based on the risk assessment perspective.