Transcript NYSSEF Powerpoint Presentation

Purpose
 To analyze, through theoretical and
experimental methods, the relative
luminescence of a series of images
produced by multiple reflections in a
decorative glass lamp
 The number of visible images can be used
to measure the sensitivity range of the eye
Background
0.25 in
11 images
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6.5 in
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3 in
Glass oil lamp from Curry
Club Restaurant, East
Setauket
Inner walls of the glass have a
partially reflective coating
Dimensions: 6.5in x 3in x 3in
Glass walls are 0.25in thick
and have a brown tint
Background (cont.)
Top View
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1st
image
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2nd
image
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3rd
image
4th
image
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When the flame is viewed at eye
level, a series of flame images can
be seen
Each consecutive image is dimmer
than the last and 11-12 images can
be seen in a dark room
The nth image is produced by n-1
reflections
The reflectance of the inner wall
determines the relative brightness
of the image
Procedure - Part 1
I2
I4
I1
Outer Surface
I8
I5
Ro = I2 / I1
t = I 6 / I5
I7
I6
Inner Surface
Ri = I7 / I6
I3
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An He-Ne laser and a photo detector were used to measure I1,
I2, I3, and I4 to calculate the reflectance of the inner and outer
surface and the absorption (t)
Incoming light split between absorption, reflection, and
transmission
Measured Intensity
Values
First Run
Second
Run
Ratio*
Average
I1
245 mA
233.8
0.95
239.4 mA
I2
7.9 mA
7.5
0.95
7.7 mA
I3
55.2 μA
53.5
0.97
54.4 μA
I4
16.3 μA
15.5
0.95
15.9 μA
* Ratio of second run to first run. The second run values are lower
because the laser power decreased after warm-up but are consistent
with the first run.
Analysis and Results
The values of Ri, Ro, and t were derived from a set of
equations that contained the measured values of I1, I2,
I3, and I4.
 t = 1-a and a = absorption ratio
Results:
 I5 = I 1 - I2
 I6 = t*I5 = t*(I1 - I2)
Ro = 3.2%
 I7 = I6 - I3 = t*(I1- I2)-I3
t = 40.8%
 I8 = t*I7 = I4 + I8*(I2/I1)
Ri = 42.5%
 t2*(I1 - I2)-t*I3 - I4/(1 - (I2/I1)) = 0
 Ro = I2/I1
 Ri = I7/I6 = 1 - I3/(t*(I1 - I2))
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Procedure - Part 2
Laser
Iris
Lamp
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5 spots of
decreasing
intensity
Photo
Detector
Laser beam allowed to travel through the lamp  5 visible spots
Photo detector used to measure their intensities in Volts using a
100 kΩ resistor & iris used to isolate the images
The ratio of the spot intensities is Ri2
Ri2 = 19.099%
Discussion /
Conclusion
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The reflectance of the inner surface of the glass lamp (Ri)
equals the relative luminescence between the flame images
Ri was measured using two independent methods and the 2
values are in very good agreement
Ri = 43.0 ± 0.5%
This value predicts the relative luminescence of the candle
flame as shown in the graph below
The nth image is approximately (0.43)n times as bright as the
first image
The 11th image is 10, 760 times brighter than the first
Therefore, the human eye can perceive a range of about
10,000 in intensity at a single instant
Future Study
Testing human visual sensitivity
 Determining an optimum reflection-transmittance
ratio (applications for sunglasses, tinted glass, etc.)
 Analyzing or designing “one-way” mirrors
 Analyzing laser cavities
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