在各大城市為路燈裝上LED燈泡之際，美國醫學學會（American Medical Association）警告，改用這項新科技有可能傷害你的眼睛。
LED燈泡節省了成本和能源，也降低我們對化石燃料的依賴。
在白熾燈泡中，有一道電流會通過燈絲，直到它的熱度足以發光。白熾燈泡因此浪費許多能源來發熱。
LED燈泡發光，是因為有正負電子在它的半導體結構中移動，但不是所有LED燈泡都對你有好處，要看它們的色溫而定。
美國醫學學會建議，晚上的戶外燈光、尤其是路燈，色溫不應該高於3000K（Kelvin）。
色溫是光譜成分的單位：一道光當中有多少藍色、綠色、黃色和紅色。
較高的色溫通常代表藍色較多，就路燈而言，這會讓它們的光看起來偏白。
白熾燈泡的色溫是2400K，藍色波長的比例遠遠不及黃色和紅色的波長。
木材上的火焰或燭光的色溫大約是1800K，大多是黃色和紅色，幾乎沒有藍色。
藍色比例偏高的LED路燈，可能會導致不適和眩光，因為在人類眼中，藍色的光比黃色和紅色更容易潰散。
藍光過強可能會損傷視網膜，而LED的光是集中的，可能會造成嚴重眩光、使眼睛疲倦。
美國醫學學會也警告，富含藍光的LED燈，對人類的生理時鐘可能會有負面的影響。
根據估計，和原先用於路燈的鈉燈相比，富含藍光的LED燈抑制褪黑激素的效果高了五倍，容易導致失眠。
因此，如果社區裡面那些亮白的新LED燈讓你感到不悅，甚至想念以前較暗的黃色路燈，你現在知道原因了。
英文原文：
As cities convert street lighting to LED bulbs, the American Medical Association is warning about the potentially harmful effect of switching to this new technology.
Converting conventional street light to energy efficient LED lighting leads to cost and energy savings, and a lower reliance on fossil-based fuels as well.
With incandescent bulbs, an electric current is passed through a wire filament until it becomes hot enough to emit light. Incandescent bulbs therefore waste a lot of energy as heat.
An LED bulb produces light when positive and negative electrons move around within its semiconductor structure. But not all LEDs are good for you, depending on their color temperature.
The American Medical Association recommends that outdoor lighting at night, particularly street lighting, should have a color temperature of no greater than 3000 Kelvin.
Color temperature is a measure of spectral content: how much blue, green, yellow and red is in a light.
A higher color temperature generally means more blue content, which in the case of street lights causes them to appear white to the naked eye.
An incandescent bulb has a color temperature of 2400 Kelvin, containing far less blue and far more yellow and red wavelengths.
A flame from wood or a candle burning has a color temperature of about 1800 Kelvin, mostly yellow and red with almost no blue.
Blue-rich LED street lighting can cause discomfort and glare. This is because blue light scatters more in the human eye than yellow and red.
Sufficient levels of blue light can damage the retina. And LED light is concentrated, which can cause severe glare, resulting in strained eyes.
The American Medical Association also warns that blue-rich LED light can have a negative impact on human circadian rhythmicity.
Blue-rich LED light is estimated to be five times more effective at suppressing melatonin at night than the sodium lamps previously used for street lighting, causing sleeplessness.
So if you were annoyed by those bright new white LED lights in your neighborhood, and missed the old, dimmer yellow street lights, now you know why.
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