Familiarization with light-matter interaction

Several images demonstrating light-matter interaction was taken during the course. Pictures taken were gathered in the perimeter of the NIP. Pictures taken is shown as such:

Specular Reflection

The picture above depicts reflection of light, specifically specular reflection or mirror-like according to wikipedia. This is kind of reflection usually occurs in smooth surfaces like mirrors, metal coated surfaces like the one above also in water or glass. Specular reflection forms images. If the surface is flat, images formed seemed to reverse while if the surface is curved, magnification or demagnification occurs .

Diffuse reflection

If one can see, there is a shade of green in the yellow t-shirt. This is due to the diffuse reflection of the leaf. This kind of reflection occurs mostly in a rough surface. Since the surface is rough, the light rays reflects to all the directions that is why the image is not preserved. However, the energy of the reflected light is preserved.

Absorption

A black object is a prime example of absorption. The reason why it is not advisable to wear black on a sunny day is because the black pigment absorbs all color. This color is then converted in more heat via radiation. And that is what defines absorption. The energy of the photon is taken up by the object and then convert it into other forms of energy.

Transmittance

As wiki said, transmittance is the fraction of the incident light specified that passes through a sample. In this picture, the bottle is filled up with smoke. The smoke forms a colloid that either absorbs the incident light or reflects the incident light diffusely that reduces the incident light the passes through the bottle.

Interference and Diffraction

This is a Titanium dioxide thin film. Because of its small thickness, rainbows are observed. This rainbows are cause a phenomenon called diffraction. Due to interference of the incident light due to thickness variation, light is being separated into it components by this film.

Reflectance(blue)-Absorbance(red) Spectrum of a Blue watch

Reflectance spectrum of a blue watch is obtained and then plotted. In order to get the absorbance, since it is an opaque object, the value of the reflectance at each point is deducted from 1. We can assume that there is no transmittance and only the absorbance of the object minimizes the intensity of the incident light. To check if it's right, think of this: The watch has the color blue because its pigments absorbs the color blue the weakest. Therefore, in reflection, only the intensity of the color blue is dominant. And that dominant color is what we mostly see. Blue has low wavelength and the reflectance peak is at around 400nm. And in absorbance, at around 400nm, it has a low value of absorbance, and thus is weakly absorbs in that color.

Reflectance(blue)-Transmittance(red) of the glass door.

The spectrum is the reflectance of the glass door in the NIP room. It has a certain coating that reduces the intensity of the ambient light. It gives a dimming effect. Here, it reflectance is shown in the blue graph and transmittance in the red graph. Since the door is transparent/translucent, we can assume the there is no absorption present and those light that were not reflected will be transmitted. To get the trasmittance, the value of reflectance is deducted from 1. To check if it is right, think of this: The point of the glass door is to reduce the ambient light from the outside. Therefore, the visible spectrum must be reduced. And in the graph, there is a considerable amount of reflectance inside the visible spectrum. Thus, the value for reflectance is correct. The same logic goes for transmission. if you want to reduce the intensity of ambient light, the transmission in that range must be reduced. In the graph, there is a depression at the visible spectrum.

References:

Wikipedia: Reflection, Absorption, Trannsmittance

Diffraction and Interference: http://electron9.phys.utk.edu/phys136d/modules/m9/diff.htm

AP 187 Handouts and Lectures

Thanks to Gino and Mabi for their camera and intellectual inputs.

Familiarization with Properties of Light Sources

Light, according to Wikipedia, is an electromagnetic radiation of a wavelength visible to the human eye, but in general, Light can be an electromagnetic radiation of any wavelength, regardless if it is visible to the human eye or not. For this entry, the emittance spectra of different light sources will be observed.

Figure 1: Emittance Spectrum for a Blackbody radiator at different temperatures.

Notice that in figure 1, the temperature is directly proportional to the emittance of the blackbody radiator; as the temperature increases, so does the peak of the emittance. Also, as the temperature is increased, the peak seems to be shifted to the left. The emittance spectra of the blackbody radiator is given by

where h is the Planck's constant, lambda is the wavelength of radiation, c is the speed of light and T is the temperature in Kelvins. The range for the wavelength is from 350nm to 750nm, which is the range for visible light. For the case of temperatures about 6500 K and 5400 K, a color of bluish green can be observed.

Below are some of the emittance spectra of common light sources.

Figure 2: Emittance for a Light Emitting Diode.


Figure 3: Emittance Spectra for a lighter that uses butane.


Figure 4: Emittance Spectra for a Mercury Lamp.

These emittance spectra were experimentally gathered using a portable spectrometer. Note that the peaks indicate the wavelength (and hence the color) in which the human eye can see the radiation. For the LED, it is expected to see a bluish-green color, while for the lighter that uses butane, it is expected to observe a yellowish color and for the the mercury lamp, a combination of bluish green and light green is expected.

It is important to at least be familiar with these emission spectra because, depending on the application, certain emittance spectra are required for certain applications.

Exploring Visual Sensing of the Human Eye

The Human Eye is a very power tool for visual sensing. Using a dynamic lens system to focus light, the human eye can zoom in and out of a desired object of interest.With combinations of photoreceptors, the human eye is like a high pixel resolution camera that records the light intensity per "pixel" and transmits it to the brain. With its complex anatomical design, there are a lot of properties of vision that emerges. These sensing properties can be explored and studied for practical and scientific uses.

Let us explore the different sensing properties of the Human Eye.

First, let us identify the minimum distance at which the human eye can focus. So, by using a pen placed squarely in front of a person's face, then slowly bringing it closer towards the eyes, the distance at which the pen becomes a blurry image, that is the minimum distance at which the human eye can focus. Table 1 tabulates the minimum distance at which the right eye, left eye and both eyes can focus the pen.

Table 1: The Minimum Distance at which the Eye can Focus

Based on the two people presented in table 1, even though their right eye have the same minimum focus distance, there is a significant variation in the minimum focus distance of their left eye and both eyes.

Next, let's look at the maximum angle of peripheral vision. According to this, peripheral vision is the ability to see objects and movement outside the direct line of vision. So, in order to determine the maximum angle of peripheral vision, the person of interest must first fixate his/her gaze at a point (point A), preferably on a wall, then slowly move a vertically placed pen to the left (and then later to the right) from the point of gaze on the wall. At the point (point B) where the person can no longer see the pen, measure the angle between the point B to the person and point A to the person. It is important to take note that at all times, both eyes must be open and must only fix their gaze on point A. Table 2 tabulates the result of this procedure.

Table 2: Maximum Angle of Peripheral Vision.

Based on table 2, Person A and Person T has a significant difference between the maximum angle of their lateral peripheral vision. Take note that peripheral vision includes the ability to detect movement, which is actually an important trait for drivers or for anyone doing activities which involves the use of peripheral vision.

Now, let's examine Visual Acuity. According to this, the fovea is a tiny pit located in the eye that provides the clearest vision. It is where the photoreceptors in the eye are highly concentrated. In order to find the range at which the fovea focuses the most, the person of interest is to concentrate his/her vision at a letter in a collection of texts 9 to 12 pixel font size, eye-level and with around 25 cm distance from the brigde of the nose. Letters surrounding the designated letter is initially covered. At each time interval, a letter is slowly uncovered until the person is unable to discern the letter. Table 3 tabulates the angle pertaining to visual acuity.

Table 3: Angle of Visual Acuity. Take note that these are measured in degrees. Also, this is different from peripheral vision.

Another key feature of the human eye is its Scotopic and Photopic Vision. According to Wikipedia (pardon us for the lack of more credible references), Scotopic Vision is the vision of the eye under low light condition while Photopic Vision is the vision of the eye under well-lit conditions. To examine how the human eye responds to these types of conditions, the person of interest is subjected to an experiment that involves the setup shown in Figure 1. This setup simulates scotopic and photopic visual conditions by enclosing colored strips inside the box. Light entering this box is regulated by a small hole by varying the distance of the light source. The person is then to record the color seen as the field of observation becomes brighter. The order of color seen is then tabulated in Table 4.

Table 4. Order of color sensed with increasing brightness.

In the visual acuity experiment, the collection of texts used were from a newspaper. The letters were uncovered one at a time. There may be certain anomalies in the detection of letters for sometimes the person knows the word, thus, the brain may subconsciously provide the ample letter that the word has.This relationship of the eye and the brain must be explored. There are several experiments suggesting to study this relationship using interactive text as shown here and here too. They use these texts to somehow fool the way we see things. A similar method with collection of these types of images is needed in a proposed experiment to study this eye-brain relationship.