Photochromatic Lens

date : 06 Nov 2010
author : Abang Chik Ray ban

MALAY VERSION

Pernahkan anda melihat kaca mata hitam atau cermin mata menjadi gelap apabila terdedah kepada cahaya matahari? Teknologi jenis ini pertama kali di bagunankan oleh Corning pada lewat tahun 1960 dan di popularkan oleh Transitions pada tahun 1990. Kaca mata atau cermin mata jenis ini di sebut sebagai photochromic atau photochromatic di mana ianya adalah tindak balas bahan kimia yang mempunyai sifat istimewa untuk berubah kepada warna-warna tertentu apabila lensa cermin mata terdedah kepada pancaran cahaya UV.

Lensa photochromic mempunyai berjuta-juta molekul seperti silver chloride atau silver halide yang terdapat dalam lensa tersebut. Molekul ini menjadikan cermin mata kelihatan jernih jika terdedah pada cahaya nampak dan cahaya lampu biasa tetapi ianya akan berubah warna melalui tindak balas kimia apabila terdedah kepada Ultraviolet yang di pancarkan terus oleh matahari. Jadi bagaimanakah kaca mata jenis ini menjadi gelap? Ianya disebabkan oleh molekul-molekul tersebut akan menyerap cahaya UV tersebut dan berubah kepada bentuk yang baru. Secara kimianya, kadar kegelapan lensa cermin mata atau kaca mata jenis photochromatic ini bergantung sepnuhnya kepada kadar kemasukan atau kadar serapan molekul terhadap sinaran UV.

Warna yang bertukar oleh lens jenis photochromatic bergantung kepada perubahan molekul.

Colour being changed by photochromatic lens depends on their molecule structure.

Jadi apabila anda keluar dari rumah dengan memakai kaca mata jenis photochromatic, anda akan dapat lihat kesanya apabila lensa tersebut bertukar kepada gelap jika terdedah kepada sinaran UV. Proses ini berlaku amat pantas sekali!!!

Original Photobrown dan PhotoGrey keluaran Corning, lensanya diperbuat daripada kaca dimana molekul-molekul tersebut secara rata aturanya. Masalah dengan penggunaan lensa kaca ini dimana ketebalan yang berbeza pada cermin mata memberikan kesan gelap yang berbeza, namun hal ini di atasi dengan menggunakan lensa/lens plastic setelah populariti pengguaan lensa plastik kian popular.

Lensa plastik terlebih dahulu di rendam ke dalam chemical bath dan oleh itu cahaya UV yang menebusi lensa tersebut sehingga pada kedalaman 150 microns akan mengubah bentuk molekul tersebut berbanding pada hanya kedalaman 5 microns cermin bercoatingkan biasa. Hal ini menyebabkan kadar kegelapan lensa photochromatic berlaku secara rata. Kaedah ini dikembangkan oleh Transitions, peneraju kaca cermin photochromatic.

Ok last sekali yang paling penting Abang Chik nak terangkan, cermin jenis photchromatic hanya akan bertidak balas dengan kehadiran cahaya UV dan tidak akan bertindak balas terhadap cahaya nampak. Oleh itu jika anda berapa dalam kereta misalnya, pastinya cermin mata anda jenis photochromatic tidak akan bertukar menjadi gelap (atau warna lain bergantung kepada perubahan fizikal molekul) disebabkan terlindung dengan cermin kereta anda dan atau cermin kereta anda mempunyai tinted yang dapat menghalang sinaran UV. Untuk bertukar kepada warna gelap, ianya memerlukan kadar minimum cahaya UV yang tertentu bergantung kepada jenis, model dan pengeluar.

Faktor kehadiran sinaran UV merupakan element penting kepada photochromatic lens.
Present of Ultraviolet influence the change of photochromatic lens.

ENGLISH VERSION

Sunglasses or prescription eyeglasses that darken when exposed to the sun were first developed by Corning in the late 1960s and popularized by Transitions in the 1990s. In fact, because of the extreme popularity of the Transitions brand, these lenses are usually referred to as transition lenses. The correct term for these glasses is photochromic or photochromatic, which refers to a specific chemical reaction the lenses have to ultraviolet (UV) radiation.

Photochromic lenses have millions of molecules of substances such as silver chloride or silver halide embedded in them. The molecules are transparent to visible light in the absence of UV light, which is normal for artificial lighting. But when exposed to UV rays, as in direct sunlight, the molecules undergo a chemical process that causes them to change shape. The new molecular structure absorbs portions of the visible light, causing the lenses to darken. The number of molecules that change shape varies with the intensity of the UV rays.

When you go indoors and out of the UV light, a different chemical reaction takes place. The absence of the UV radiation causes the molecules to "snap back" to their original shape, resulting in the loss of their light absorbing properties. In both directions, the entire process happens very rapidly.

In the original PhotoBrown and PhotoGrey products made by Corning, the lenses are made of glass, and the molecules are distributed evenly throughout the entire lens. The problem with this method was apparent in prescription glasses where different parts of the lens were of varying thickness. The thicker parts would appear darker than the thinner areas. But with the increasing popularity of plastic lenses, a new method has been developed. By immersing the lenses in a chemical bath, the photochromatic molecules are actually absorbed to a depth of about 150 microns into the plastic. This is much better than a simple coating, which would only be about 5 microns thick and would not provide enough molecules to make the lenses sufficiently dark. This plastic lens absorption process has been popularized by Transitions, the leading manufacturer of photochromic lenses.

An important note about photochromic lenses, because they react to UV light and not to visible light, there are circumstances under which the darkening will not occur. A perfect example of this is in your car. Because the windshield blocks out most UV light, photochromic lenses will not darken. For this reason, most sunglasses with photochromic lenses also have a certain amount of tint already applied to them.




Originally :- Abang Chik Ray ban