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Hamsa Sridhar, Kings Park High School, Kings Park, NY; Harold Metcalf and John Noe, Laser Teaching Center, Department of Physics and Astronomy, Stony Brook University This project is based on a decorative glass lamp obtained from the Curry Club Restaurant in Setauket. The flame of the lamp is surrounded by four tinted glass panels whose inside surfaces have a partially reflective coating; the panels are arranged in the form of a rectangular prism, with opposite faces parallel to each other. When the flame is viewed from outside the lamp at eye level, a series of secondary flame images can be seen; each image appears slightly dimmer than the previous one, and about 11 images in all are visible in a darkened room. The ratio of brightness between the first image and last visible image is a direct measure of the visual sensitivity range of the eye. The purpose of this experiment is to analyze, through theoretical and experimental methods, the relative luminescence of the series of images produced by the multiple reflections. It can easily be shown that the luminescence ratio from one flame image to the next is equal to the reflectance of the inner surface of the lamp (Ri). Two independent methods were used to measure this value. In the first experiment a He-Ne laser beam was directed toward the glass lamp at a slight angle. Using a photodetector, the intensity of the initial beam and the three beams that either reflected from the two surfaces of one glass panel, or passed completely through it, were measured. These values were analyzed through a series of equations to obtain the reflectance values of the inner and outer surfaces and the absorption in the tinted glass between. In the second experiment, the laser beam was allowed to travel through the glass lamp to a screen. Five spots of decreasing intensity were visible; they were isolated by an iris and their intensities were measured using the photodetector. In this case the ratio between the spot intensities is Ri^2, and this value could be accurately determined by a graphical analysis. The first experiment yielded Ri = 42.5% whereas the second experiment gave Ri = 43.6%. The two values are in good agreement and we adopt their average, 43.0 � 0.5%, as the final result. It follows that the nth visible image must be (0.43)^(n-1) times as bright as the first (unreflected) image, or 4,627 times as bright for n = 11. Therefore, the human eye can perceive an intensity range of about 5,000 at a single instant.
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