Activity 2: I See The Light!
Posted on: August 20, 2010
Around July last year, Troy and I both got Macbooks of our own. Troy’s Macbook was the the 2009 Unibody Aluminium Macbook, while mine was the 2007 Macbook Pro model. Pretending to be geeks, we usually subjected our laptops to comparison. Processor speed, RAM, multimedia capabilities, our laptops were almost at par with each other.
Everything except for the hard disk space and display, we thought.
It was widely known that by 2008, Apple made the shift from discrete models to unibody models at the same time also changing from CCFL backlighting to LED backlighting. Because of that we automatically thought that all Macbooks pre-2008 were CCFL lit and Macbooks manufactured after that were LED lit. We then concluded that Troy’s backlighting was superior compared to mine, as his LCD was backlit with LEDs, while mine old CCFLs.
We now fast forward to today. Our early lessons in our AP187 class under ma’am Jing mostly dealt with color science. Talking about colors we were taught how to profile different light sources using the light source’s spectra, which are composed of combinations of intensities of different wavelengths.
This activity was done in two parts. First we were required to emulate the emittance spectrum of blackbody radiation. Next is that we were asked to measure the emittance spectrum from different light sources using a spectroradiometer.
So what did my intriguing introduction have to do with our activity? Well, we thought that it would be interesting to compare the spectra of our Macbook’s to see if there really was any difference between the two. So for the results of our little experiment, just read on.😉
Blackbody Radiation
According to Wikipedia, a blackbody is an object that “absorb and incandescently re-emit radiation in a characteristic, continuous spectrum.” [1] It is called a black body because when the object is cold or of low temperature, it is, well, black.
What is most interesting about blackbodies that though they don’t emit colors when they are cold, but upon heating it to different temperatures the blackbody radiates colors from different spectra following the equation below
where S is the spectral energy, λ is the wavelength, T is the temperature in Kelvin, c is the speed of light, k is the Boltzmann’s constant, and h is Planck’s constant.
This formula was simulated for temperatures of 1000K, 2500L, 5400K and 6500K and is plotted below.
Based on the plotted values, we can say that upon heating of lower temperatures (1000K), the blackbody would radiate colors of higher wavelength which are the regions of color red. As we increase the temperature, the spectrum shifts towards the shorter wavelengths. This means that the color of the blackbody becomes brighter and more bluish in nature in higher temperatures.
Spectra of Different Light Sources.
So here is the interesting part of the experiment. We got hold of a, drum roll please, spectroradiometer! According to Wikipedia (gosh I have to stop quoting Wikipedia), a spectroradiometer is an instrument “designed to measure the spectral power distributions of illuminants.” [2] This is done by first splitting the light from a source using a grating. As the light is split into its component spectrum, the different intensities from different wavelengths are captured and measured using a detector. [3]
Equipped with a spectroradiometer, we measured the spectra of the displays of different gadgets, namely the mid-2007 Macbook Pro (alias Pepper), an early 2008 black Macbook(alias Russel), the 2009 Unibody Macbook (alias Baked mac), a Lenovo laptop (alias dela Rosa), and an iPhone 3Gs.
To measure the spectrum, what we did was we set the brightness of the gadgets at the highest level (ouch), flashed a blank white background and then recorded the spectra. The results left us in surprise.
So why were we surprised? We expected that the spectrum for the 2007 Macbook Pro and 2008 black Macbook to be similar, but the results show otherwise. Our results can be grouped into two, with the first group being the Lenovo and black Macbook, and the second group being the 2007 Macbook Pro, 2009 Macbook and iPhone 3Gs.
We were so confused at first, because we really thought that the 2007 Macbook Pro wasn’t lit by LEDs, since there were few display technologies that used LED backlights in 2007. But apparently, upon further research, we discovered that the 2007 Macbook Pro was indeed lit by LEDs [4]. Ha! And again, Pepper was at par with Baked Mac.
Further research still reveals the spectra for CCFLs and white LEDs used for backlighting
The spectrum of a white LED [5]
The spectrum of a CCFL [6]
Comparing these data gathered from the internet, we can say that indeed, the Lenovo laptop and black Macbook were lit by CCFLs while the Macbook Pro, Macbook 2009 and iPhone were lit by LEDs.
Conclusion
So what did we learn from all this hullaballo? Apparently, just by looking at the spectra of the light emitted by something, we can discover what emits the light. So for more advanced applications, knowing the spectrum of different elements, we can see what kind of elements a light emitting object, say the sun or the stars, contain. And that, my friends, is an application way cooler beyond getting the spectrum of displays.
But hey, we’re happy to discover that at 2007, Pepper was state of the art.
For this activity, we give ourselves 10/10, for we were able to produce all outputs needed.😉
Thank yous
Ma’am Jing for answering our questions
Milli for helping us with the spectrometer
Pat for lending us Russel.😉
VIP for lending us the spectrometer and dela Rosa.
Disclaimer
Why were we so amazed? Well in the group, I, BA was the most amazed since I didn’t know that Pepper had so much advanced technology. I bought Pepper second hand from my uncle in US and I overly under-estimated this laptop’s powers since it was already old (2 years old is already old for a laptop in these days). Only now that Pepper is surprising me by letting me discover more and more of her power.
References
[1] Black body – Wikipedia, the Free Encyclopedia (http://en.wikipedia.org/wiki/Black_body)
[2] Spectroradiometer – Wikipedia, the Free Encyclopedia (http://en.wikipedia.org/wiki/Spectroradiometer)
[3] Smathers, Michael O., “How Does a Spectrometer Work?” (http://www.ehow.com/how-does_5256312_spectrometer-work.html)
[4] Mohns, Robert, “Review: MacBook Pro (15″ LED)” (http://www.macintouch.com/reviews/mbp15led/)
[5] “White LED tips” (http://www.trainweb.org/girr/tips/tips7/white_led_tips.html)
[6] “Wellypower Optronics” (http://www.wellypower.com.tw/english/qa_2.php?function_page=e#3)
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