Why Are Some Headlights Blue-High Intensity Discharge Lamps

高強度氣體放電（High-intensity discharge，簡稱HID）燈泡包含了下列這些種類的電燈：水銀燈、金屬鹵化燈（也稱作HQI）、高壓鈉燈、低壓鈉燈、高壓水銀燈，以及較少見的短弧氙氣燈。這些燈泡種類的發光元件是一顆置于耐高溫燈管（弧光管）內安定的電弧放電器，并有超過 3 W/cm2 (19.4 W/in.2) 的發光能力。

HID 燈通常應用在大面積區域且需要高品質的光線時，或針對能源效率、光源密度等特殊要求時。這些地方包括體育館、大面積的公共區域、倉庫、電影院、戶外活動區域、道路、停車場或巷道。最近 HID 燈如金屬鹵化燈，常被用于零售店和住宅環境。HID 燈更實現到室內栽培上，特別是一些需要高品質強光的植物，如蔬菜和花卉。它們也可用于室內水族館，重建近似于熱帶地區的強光。

 

有些 HID 燈像是水銀燈會發出大量的紫外線，因此需要擴散器（diffusers）來阻擋紫外線的輻射。近幾年來經常發生幾個案件，因為瑕疵的擴散器，造成人們受到嚴重曬傷和電弧眼?，F在均以規格來監控燈泡品質，否則燈泡會因為外層燈管破裂就馬上燒掉。

最近 HID 燈常被使用于汽機車的頭燈。這項應用在汽機車業界仍有各種不同的意見，主要在于 HID 燈有時會導致讓人刺眼的強光。業界通常使用自動轉向頭燈（Automatic Self-leveling System）來降低這個問題，但這類的配備在大多車種都是昂貴的選配規格。然而，許多業者偏好使用這類光線，因為他們比一般頭燈能發出較清澈、較明亮、較自然的光線。

Have you ever been driving along a country road at night, and all of a sudden a car comes around the bend and shines their high beams right into your eyes? Ugh, they’re so bright!

High Intensity Discharge Lamps

You also notice that their lights look a bit bluer than you’re used to. That’s because they might be. Regular headlights are made up of white light, which is a combination of all colors of the rainbow.

But these blue lights, while still containing a mixture of all colors, contain more blue wavelengths, making them appear more blue to our eyes.

Many luxury cars have these types of lights, called High Intensity Discharge lamps, because the headlights seem brighter under most conditions.

What Happens In Fog?

They actually make visibility worse.

Fog is made up of suspended water particles in the air, like a cloud settled down on the earth. But blue light scatters more effectively off these water particles than regular headlights do.

This is because the shorter the wavelengths of light, the better it scatters off of air and water particles.

Blue Light

So blue light, which has very short wavelengths, is much more likely to scatter than the longer wavelengths, like red light.

This means that when blue light hits the water particles, it’s more likely bounce off, going back into your eyes, and reducing your ability to see through the fog.

It also increases the glare for everyone, since blue light scatters better inside our eyes as well. In the regular headlights, there are still a fair amount of smaller wavelengths, so it scatters too. But since it also has more of the longer wavelengths, more light gets through the fog. So you can still see–sort of.