Fake glasses although not increase the intensity of ultraviolet rays, but passes them to a greater extent than the visible, thus creating imbalance. The lens extends, causing harmful radiation affects him more than the absence of sunglasses at all. If the forgery is positioned as polarized glasses actually polarizers in the product can not be.
Spend experience - put under UV currency detector office sheet of plain paper. In contrast to the bill, it glows bright blue light. Now skip detector light bulb through sunglasses - if the paper is still lit, the accessory is a fake, and carry it dangerous. But the big currency detector, includes an outlet store in points with a not take, so you'll have to buy a small, battery-operated.
But the device for checking the polarization properties of spectacle glasses and so is in every pocket. This - the mobile phone (except those equipped with a display type AMOLED). Just put on your glasses and look at the screen. Spin the phone in your hand - whether there are on it seemingly dark spots? If so, the glass really is polarizing. But remember that even at such points should also check the transmittance of ultraviolet radiation. Remember that polarized glasses may not be, but are obliged to detain ultraviolet.
And another tip. Choosing sunglasses without polarization properties, prefer models, which have a glass yellowish or brownish tone. But beware of blue or purple: that they miss ultraviolet, there is no doubt even without checking devices.