The Research of UV Transmittance of Tinted Plastic Lens 染色光學塑膠鏡片對紫外線穿透率影響程度之研究

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1 The Research of Transmittance of Tinted Plastic Lens 染色光學塑膠鏡片對紫外線穿透率影響程度之研究 Shih-Chang Lin 1, Der-Chin Chen 2, Shih-Wen Lee 3, Cheng-Hen Chiu 4 1 林世章 2 3 陳德請李世文 4 邱振恆 1 逢甲大學資訊電機工程系碩士班學生 2 逢甲大學資訊電機工程系副教授 3 中華科技大學電機工程系助理教授 4 中台科技大學視光系講師 Department of Electrical Engineering, Feng Chia University 3 Department of Electrical Engineering, China University of Science and Technology 4 Department of Optometry, Central Taiwan University of Science and Technology 摘要本研究目的在建立鏡片染色的流程與染色鏡片 穿透率光學特性的量測技術 實驗中使用光譜儀與 光源對未具抗 與具抗 的兩組鏡片進行 穿透率量測, 進一步對不同深淺顏色抗 鏡片的穿透率特性進行分析 實驗結果具抗 鏡片抗 效果比未具抗 鏡片好 ; 在深色系列, 深綠色抗 鏡片會比深紅色與深藍色抗 鏡片上更有阻隔 效果 ; 然而在淺色系列, 淺紅色抗 鏡片會淺綠色與藍淺色的抗 鏡片阻隔紫外光的效果比較好 穿透率量測數據結果可做為消費者做抗 鏡片選擇之依據 關鍵字 : 鏡片染色 紫外檢測 鏡片色彩 ABSTRACT The purpose of this research is to set up the dyeing process of the plastic lens and measure the transmittance of the tinted plastic lenses which include -absorbing and non- absorbing. In experiment, the spectrometer (USB 2000) is used to measure the transmittance in both cases. Furthermore, the characters of the transmittance in different deep and light colors of the -absorbing tinted plastic lenses are compared. The results of the experiment in the -absorbing tinted plastic lenses are: the effect of the -absorbing tinted plastic lens better than that of non- absorbing tinted plastic lens. Among the deep color series, in the effects of -absorbing tinted plastic lens are: the deep green color is better than the deep red and blue colors. However, 81

2 The Research of Transmittance of Tinted Plastic Lens among the light color series, in the effects of -absorbing tinted plastic lens are: the light red color is better than light green and blue colors. According to the results, the consumers can have more choices in the -absorbing tinted plastic lenses. Keywords: Lens dyeing ultraviolet () inspection Lens color Ι. INTRODUCTION The tinted plastic lenses which are intended for use in an outdoor or other adverse environment include sports field, such as, winter sports including skiing, snowboarding, snowmobiling, or motorcycle and summer use, as well as safety eyeglass. Other eye protecting optical elements include masks for helmets, and visors. The tinted plastic lenses are permanently colored lenses, which mean that the lenses will never change their tints. Plastic lenses acquire tints through a warm color bath, during which the lenses achieve different shades of darkness according to the bath time. It can reduce glare caused by light and fashion tints. In general, the plastic lenses are easy to tint, but lenses made of glass or those covered with protective coatings will not absorb the dye properly. The type of the eyeglass are the tinted plastic lenses, protective lenses, hard coated lenses, anti-reflected coated lenses, polycarbonate, acrylic lens and tinting perfect gradient lenses. Such the tinted plastic lenses may be a single plastic lens or a double plastic lens, and such lenses can be tinted in various colors to assist in contrast and glare protection. Certain improved contrast resolution performances have been available in fixed glass lenses for sunglasses and eyeglasses, such as, eyewear having a red or other colored lens which assists in contrast resolution performances. The eyeglasses have a removable plastic lens which is tinted in a manner to improve contrast resolution for a wide variety of light levels of sunlight and glare. The tint is adapted to the plastic materials usable in eyeglasses lenses to provide improved anti-fogging characteristics and visual performance. In particular, the tint creates a transmission curve characterized by several peaks and valleys along the visible wavelength spectrum which conforms to certain characteristics of the human eye to improve contrast in a removable plastic lens for skiing, summer and other outdoor sports. The spectrum is divided into three bands: A (320 to 400 nm), B (280 to 320 nm), and C (100 to 280 nm). Each band has shown to be absorbed differently by ocular tissues. A, the closest band to the visible spectrum, is preferentially absorbed by the cornea and retina. B is mainly absorbed by the crystalline lens and partially by the retina. C is typically filtered out by the ozone in the atmosphere. absorbing eyeglasses 82

3 decrease the amount of ocular exposure to ultraviolet radiation versus non- absorbing eyeglasses. The reported protection levels from a number of studies of various absorbing eyeglasses show that the transmittance spectra are consistent with, or better than, the protection offered by eyeglasses, when comparing the transmittance spectra of the various ophthalmic materials (e.g. glass, plastic) and considering the effects of the atmosphere on C transmittance. II. REFLECTANCE AND TRANSMITTANCE Consider a circular beam of light incident on a surface, as shown in Fig.1, such that there is an illuminated spot of area A. Recall that the power per unit area crossing a surface in vacuum whose normal line is parallel to, the Poynting vector, is given by (1) Furthermore, the radiant flux density (W/ ) or irradiance is (2) Acos i Acos r i r n i A n t Acos t Fig.1 Reflection and transmission of an incident beam This is the average energy per unit time crossing a unit area normal to (in isotropic media is parallel to ). In the case at hand Fig.2, let and be the incident, reflected and transmitted flux densities, respectively. The cross-sectional areas of the incident, reflected and transmitted beams are, respectively, and. Accordingly, the incident power is ; this is the energy per unit time flowing in the incident beam, and it s therefore the power arriving on the surface over A. Similarly, is the power in the reflected beam, and is the power 83

4 The Research of Transmittance of Tinted Plastic Lens being transmitted through A. We define the reflectance R to be the ratio of the reflected power (or flux) to the incident power: (3) In the same way, the transmittance T is defined as the ratio of the transmitted power to the incident power and is given by (4) The quotient equals reflected waves are in the same medium,, and since the incident and =, =, and (5) Similarly, are assumed, (6) Where the facts of both and are used. Notice that at the normal incidence, where a situation of great practical interest is,, both the transmittance in Eq.( 4) and the reflectance in Eq.(3) are then simplified by the ratios of the corresponding irradiances. Since, not necessarily considering the sign of r in any particular formulation, and the reflectance, R, in Eq.(5) is a clear notation and easy to remember. Observe that the transmittance, T, in Eq.(6), is not in a simplified expression, that is, not simply equals to [1-4]. 84

5 interface Transmitting medium Fig. 2 Reflection and transmission of an incident beam III. EXPERIMENT AND DISCUSSION The conditions and specifications used for the experiment are listed in Table 1. This system consists of three parts, USB2000 spectrometer, light lamp and standard optical plate which calibrate transmittance of spectrometer [5]. The USB 2000 spectrometer is an optical measurement instrument based on a diffraction grating and a one-dimensional CCD detector array. The CCD array has pixels so the spectrum reads out as a list of 2048 data numbers. Light enters via a slit located at the bottom of a threaded receptacle, which can be used to connect an optical fiber that is terminated with a SMA plug. This instrument achieves a spectral resolution of about 0.5 nm between wavelengths of 375 to 1100 nm. Due to the sophisticated experiments, the procedures are divided into two parts: Part 1: tinted process The material used is: hard resin lens (CR39, n=1.5, SPH:-0.00D, CYL:-0.00D). The tinted procedures are described as follows: A. Turn on the tint machine and heat up to about 90. Follow the directions in the tint machine, a light should be appeared once it has heated to the appropriate temperature. If the tinted plastic lens is used to block ultraviolet light, the plastic lens is ready to be dyed. Mix the dye packets in the plastic lens with dye solution and pour the mixture into the tint machine's tray. The tint machine will heat the dye. The amount of time it takes to heat the dye does vary depending on the type of machine you are using, so consult the tint machine's manual or directions. B. Put the plastic lenses into the lens s holders once the dye has been heated to the appropriate temperature and clamp them in place. Lower the plastic lenses into the 85

6 The Research of Transmittance of Tinted Plastic Lens dye. The amount of time you leave the plastic lenses in the dye will depend on how deep you want the tint to be. For a light tint, leave them in for less than a minute. For a medium tint, leave them in for no more than two minutes. For a deep tint, you can leave them in for a few hours. C. Raise the plastic lenses out of the dye, remove the clamps and put the plastic lenses on the clean cloth. Inspect the transmittance of plastic lenses to determine if they are the deep or light tint you wish and if both plastic lenses are of the same concentration. If you would like a deeper tint on one or both of the plastic lenses, place one or both of them in the dye solution until they are of the concentration you wish. D. Allow the dye to dry on the plastic lenses for an hour once having the appropriate concentration. Clean the lenses with lens-cleaning solution and an optical cloth. Part 2: the measurement of transmittance A. Divide the tinted plastic lenses into two types, the first type is the -absorbing and the second type is reference plastic lens, non -absorbing. B. The experimental setup is shown in Fig. 3. The position of ultraviolet lamp and USB2000 spectrometer is set in the table. Adjust the ultraviolet lamp to optimize intensity and the position of tinted plastic lens. The distance between the ultraviolet lamp and spectrometer is 60cm. C. Put the tinted lens about 1.2cm~1.5cm in front of the spectrometer, that is, the distance between the glasses and eyes. D. Measure the transmittance of the tinted plastic lens and reference plastic lens The fashion tints for cosmetic are usually light pink, brown or gray; tints on plastic lenses are mostly darker colors such as brown and gray. Yellow tints can block out blue light and green is sometimes used in sunglasses, as an alternative to common tints such as gray and brown. The tinted plastic lens of this paper are classified according to the transmittance of light, there are three colors: ocean blue, peony red, olive green respectively. The transmittances of tinted plastic lens in the spectral region are measured, and the capability of -absorbing of the tinted plastic lens is obtained. Furthermore, the -absorbing performance of the tinted plastic lens of deep or light color is acquired. 86

7 The experiment results are shown in Table 2 and Table 3. From the results, the ultraviolet transmittance of the non -absorbing tinted plastic lens and perfect - absorbing tinted plastic lens are about 100% and 0%, respectively. Tinted Plastic Lens Lamp 60 cm 1.5cm Spectrometer (USB 2000) Fig. 3 Experimental setup Table 1 the experimental conditions and specifications Detector type Number of elements Pixel size Detector range Signal-to-noise ratio A/D resolution Dynamic range Gratings Focal length Optical resolution Fiber optic connector lamp linear silicon CCD array 2048 pixels 14 μm x 200 μm 375nm-1100 nm 250:1 (at full signal) 12 bit 2 x 108 (system); 2000:1 for a single scan 14 gratings; through Shortwave NIR f/4, 42 mm (input); 68 mm (output) 0.5 nm FWHM (depending on grating and size of entrance aperture) SMA 905 to single-strand optical fiber (0.22 NA) The spectrum range is 375nm~650nm tinted plastic lenses -absorbing and non -absorbing 87

8 The Research of Transmittance of Tinted Plastic Lens Table 2 The tinted plastic lens without -absorbing wavelength absorbing blue 0 blue 1 blue 2 blue 3 blue 0 blue 1 blue 2 blue 3 absorbance transmittance 0% 56.46% 57.52% 60% 65.64% 53.49% 55.42% 55.55% 64.24% 100% 43.54% 42.48% 40% 34.36% 46.51% 44.58% 44.45% 35.76% Table 3 The tinted plastic lens with -absorbing wavelength absorbing blue 0 blue 1 blue 2 blue 3 blue 0 blue 1 blue 2 blue 3 absorbance transmittance 0% 89.49% 89.44% 89.47% 89.46% 89.49% 89.48% 89.46% 89.44% 100% 10.51% 10.56% 10.53% 10.54% 10.51% 10.52% 10.54% 10.56% IV. CONCLUTION From the experimental results, the light transmittance of tinted plastic lens with -absorbing should be 10.56% better than the 35.76% of the tinted plastic lens without -absorbing. The ultraviolet transmittance of perfect - absorbing tinted plastic lens are about 100%. The characteristics of the transmittance in different deep and light colors of the -absorbing tinted plastic lenses are also compared in this paper. In deep color series, the effects of the -absorbing tinted plastic lens are: the deep green color better than the deep red and deep blue colors. However, among the light color series, the effects of the -absorbing tinted plastic lens are: the light red color is better than both the light green and the light blue colors. According to these results, there are more available choices in the -absorbing tinted plastic lenses for the consumers. The tinted plastic lens can reduce glare caused by light and fashion tints. 88

9 ACKNOWLEDGEMENT The authors would like to give a great deal of thanks to National Science Council (NSC E D) in Taiwan which offers funds for this research. REFERENCES [1] Kai Wu, Cheng-Chung Lee, Neal J. Brock, and Brad Kimbrough, Multilayer thin-film inspection through measurements of reflection coefficients, Optical Society of America, Vol. 36, No. 16, August 15, 2011 [2] Hongyun Wang, Zhengshang Da, Lili Liu, and Juanning Zhao, Optical transmittance measurement system for coated elements with low transmittance, Optical Society of America, Vol. 51, No. 13, May [3] Tomoharu Hasegawa, High Refractive Index Bi 2 O 3 - B 2 O 3 -TeO 2 Glass with High Visible-NIR Transmittance, Optical Society of America, [4] Kuo-Yung Hung,Liang-Wei Chang, Fan-Gang Tseng, Nguyen Thi Minh Hang, Optimum Electrostatic Force Control for Fabricating a Hybrid -Curable Aspheric Lens, IEEE, January 20-23, [5] USB2000 Fiber Optic Spectrometer Installation and Operating Manual, Optics, Inc.,