subject: Day night glasses | Sunglass For Womens [print this page] Transition lenses are a type of photochromic lenses that automatically darken when they are exposed to the sun's harmful ultraviolet rays, and come back to their original clear state once a person is away from sunlight. How do transition lenses work and are there any problems involved with these eyeglasses? That is what we will be finding out in this article.The transition lenses work because they have photochromic properties. The photochromic properties are brought about because of their ability to change tints in UVB and UV rays. These tints are made possible due to a particular patented dye that helps to activate the lens. This dye is embedded in the form of micro-crystalline silver halides or molecules in a glass substrate. These silver halides are usually taken in the form of silver chloride and work for pieces that are made from a glass material. Similarly, for glasses that are made from a plastic material, organic photochromic molecules are used so that the reversible effect can be achieved. These molecules are usually taken in the form of oxazines or naphthopyrans.As said before, these lenses (or rather the properties in the lenses) react to the UV rays and begin to turn darker as a reaction to the rays. These will begin to darken in less than a minute when they come in contact with the UV rays and will continue to darken very slightly over a period until they finally adjust to allow only a stipulated amount of light to enter the eye. They do not darken to the point of turning into sunglasses. The minute a person gets away from the UV rays, the lens start to fade and come back to their normal color. This takes about 15 minutes and many say that the change is not even noticeable. These do not work as effectively in vehicles because a car's glasses are already protected from the UV rays.Every individual has a very different face shape and structure. Even though there are many who have similar shaped faces, there are no two people, with the exact same structure or face builds (not even twins). Some have broad foreheads, while some tiny eyes, some a big nose, while some have plump cheeks! With such a variety of faces in the world, choosing a glass frame can be difficult. If you have eyeglasses, you have to make sure, the shape and size of the frame suits your face. Thus, many designers have come up with a variety of styles and shapes, which will give you the liberty to choose your favorites. Once you pick a frame, you will use it for at least 6 months, making it a part of your daily look! Therefore make sure, you pick the right glasses for face shape, and if you need help, scroll through the following article.If you are new to glasses or want to change your frames, there's always a question about what are the best glasses for face shape. To start the search for choosing glasses for face shape, you need to first find out what is your face shape and structure so, to make the right choice of frames. This is necessary if you want to wear any kind of face accessories like earrings, nose rings, sunglasses, etc. other than glasses. There are many easy ways to know the different face shapes, like either judge for yourself or make someone else do it. We here, have a few common shapes which are observed in people, and the right glasses for face shape, so take a look.Oval Faces This is a very common face shape observed in many individuals. When your face is longer than its width, the shape is known as oval. Since this is a very common face shape that occurs, frames with vertical height or elongated ones, can surely make the face short and balanced. Oval faces also have extended cheeks and frames which are deep from top to bottom, conceal the sections of these cheeks. If you want, you can surely look for other shapes and colors which suit your face.Round Faces Round faces have curved outlines and the overall width and length of the face are almost the same. For this type of face structure, you can go for angular and narrow pair of glasses. The reason you can use these frames is that, it lengthens the face and makes the round face look thinner. Rectangular shaped reading glasses with broad frames, surely look great Another shape observed is the square shaped face, where the width, length and other dimensions of the face are the same. They have a broad forehead and a strong jawline. Glasses for face shapes like these should have wider frames than being longer. This will not only reduce the facial angles which accentuate the square face, but will make the face look curvy and lengthened. Thin frames with oval lenses also look great on square faced people. If you want you can simply have frame-less glasses with circular or oval eyeglass lenses types.Oblong faces are also known as heart shaped faces as they are broader at the foreheads and taper towards the chin. They are long and wide but on the two opposite sides which actually give them the perfect attractive look in all the face shapes. As all you have to do is make such faces look little shorter, picking glasses for face shapes like these can be easy, such as deep and wide frames with rectangular glasses. They make the face look shorter from the width and thus give them a great look. A diamond shaped face is also oblong in many ways and the best frames that suit such are the outstretched horizontal or round eyeglass frames.
