categoriesDepending upon their lumi

categoriesDepending upon their luminous transmittance at their reference point, sunglass filters for general use shall be attributed to one of five filter categories. Unless the filter is one of the following, category 0 shall not be claimed:— a filter for which specific protection against any part of the solar spectrum is claimed;— a photochromic filter in its faded state.The range of the luminous transmittance of these five categories is given by the values in Table 1. An overlap of the transmittance values shall be not more than ± 2 % (absolute) between the categories 0, 1, 2 and 3. There is no overlap in transmittance values between categories 3 and 4.The maximum deviation for declared luminous transmittance value shall be ± 3 % absolute for the transmittance values falling in categories 0 to 3 and ± 30 % relative to the stated value for the transmittance values falling in category 4.When describing the transmittance properties of photochromic filters, two categories for transmittance values are generally used. These two values correspond to the faded state and to the darkened state of the filter.In the case of gradient filters, the transmittance value at the reference point shall be used to characterize the luminous transmittance and the category of the filter.For gradient filters, the overlap in luminous transmittance allowed between categories shall be double that for uniformly tinted filters.Table 1 also specifies the UV requirements for sunglass filters for general use and, when the filters are claimed by the manufacturer to protect against IR radiation, the IR requirements.