1. The principle of lens UV transmittance detection
The transmittance measurement of sunglasses lenses cannot be processed as a simple average of the spectral transmittance at each wavelength, but should be obtained by weighted integration of the spectral transmittance according to the weight of different wavelengths. The human eye is a simple optical system. When evaluating the quality of glasses, the sensitivity of the human eye to light radiation of different wavelengths must first be considered. In short, the human eye is sensitive to green light, so the transmittance of the green light band has a great influence on the light transmittance of the lens, that is, the weight of the green light band is greater; on the contrary, because the human eye is not sensitive to purple light and red light, so The transmittance of purple light and red light has a relatively small effect on the light transmittance of the lens, that is, the weight of the purple light and red light band is also relatively small. An effective way to detect the anti-ultraviolet performance of lenses is to quantitatively determine and analyze the transmittance of UVA and UVB spectra.
2. Testing equipment and methods
The spectral transmittance tester can be used to measure the spectral transmittance of sunglasses in the ultraviolet region to determine the quality of the sample’s ultraviolet transmittance. Connect the spectral transmittance meter to the computer serial port, start the operating program, perform environmental calibration at 23°C±5°C (before calibration, it must be confirmed that the measuring part has no lens or filter), and set the test wavelength range to 280～480 nm, observe the ultraviolet rays of the lens under the condition of magnification of the transmittance curve. Finally, place the tested lenses on the test rubber plugs to test the light transmittance (note: wipe the lenses and the test rubber plugs clean before testing).
3. Problems in the measurement
In the detection of sunglasses, the transmittance calculation of the ultraviolet band adopts a simple method of averaging the spectral transmittance, which is defined as the average transmittance. For the same sample under test, if the two definitions of QB2457 and ISO8980-3 are used for measurement, the results of the ultraviolet waveband transmittance obtained are completely different. When measured according to the definition of ISO8980-3, the calculated result of the transmittance in the UV-B band is 60.7%; and if measured according to the definition of QB2457, the calculated result of the transmittance in the UV-B band is 47.1%. The results differed by 13.6%. It can be seen that the difference in the reference standard will directly lead to the difference in the technical requirements, and ultimately affect the accuracy and objectivity of the measurement results. When measuring the transmittance of eyewear products, this problem cannot be ignored.
The transmittance of sunglasses products and lens materials is tested and analyzed, and the accurate value is obtained by weighted integration of the spectral transmittance, and the results of the pros and cons of the sunglasses products are obtained. First of all, it depends on whether the material of the lens can block ultraviolet rays, UVA and UVB, and can transmit more visible light to achieve anti-glare function. Experiments have shown that the transmission performance of resin lenses is the best, followed by glass lenses, and crystal lenses are the worst. The transmission performance of CR-39 lenses among resin lenses is far better than PMMA.
Post time: Nov-10-2021