Activity 2: Familiarization with Properties of Light Sources

Familiarization with Properties of Light Sources

Light, as defined by physics, exhibits properties of both waves and particles.  It propagates at speed of approximately 3x10⁸ m/s [1-3].

In this activity, we measured the emittance spectrum of different light sources. In our case, we measured the red, green and blue spectrum of the screen of TOSHIBA Satellite L510 model.  Then after that, simulated a blackbody radiation that has a temperature that ranges from 1000 Kelvin to 6500 Kelvin.  We will be analyzing the spectral emittance of various objects.  This phenomenon is dependent on temperature and the wavelength as given by the Planck's Equation in Spectral energy Density Form defined as,

Eq.1: Planck's Equation in Spectral Density Form

by the Planck's Equation in Spectral energy Density Form defined ,where h is the Planck's constant having a value of 6.62608 x 10^-31 Js, λ is the wavelength of radiation, c is the speed of light, k is the Boltzmann constant which has a value of 1.3806503 × 10^-23 m² kg s^-2 K^-1 and T is the temperature in Kelvin [4].

From (Eq. 1), we can theoretically say that as we increase the temperature, the spectrum shifts to the lower wavelengths.  Meaning, the blackbody shifts to the UV part as the temperature increases.

 

Results and Discussions:

Using the spectroradiometer, we measured the emitted spectra of the laptop screen.  Shown below is the plot of the three spectra namely red, green and blue.

Fig. 1: Spectra measurement of red, blue and green from the screen of the laptop.

From this plot, it is clearly evident the separation of colors taken from the screen of the laptop.  The blue line is the measurement of the spectrum of the red background of the screen.  It shows that the curve produced is near to the standard wavelength of red which is 632.8 nm, we think that the extra peak from this curve is due to the light produced from the screen of the laptop.  On the other hand, the red curve is the measurement of the spectrum of the green background and the green line is the spectral measurement of the blue background.  Both are near the standard wavelength of green and blue respectively.

Other measurements were done on different sources.  Shown below are the measurements of fluorescent, incandescent lamp and oven.

Fig. 2: Spectra measurement of a fluorescent lamp.

Fig. 3: Spectra measurement of an incandescent bulb.

Fig. 4: Spectra measurement of an oven.

It can be observed that the resulting spectra of the fluorescent lamp seems to be the convolution of the spectrum of the mercury vapor and the fluorescence of the phosphor in the lamp.  On the other hand, the broad peak observed from the incandescent bulb corresponds to the yellowish color that it emits.  Lastly, there is no conclusive argument for the measured spectrum for the oven because the signal is noisy.

Next is the simulation of the blackbody radiation.

Video clip1: Simulation of Planck's Blackbody Law.

Aivin, simulated the blackbody radiation and it was seen that from the video clip, as the temperature increases, the emittance of the blackbody shifts to the UV wavelength.  In layman's term, the blackbody turns to blue and becomes brighter as the temperature increases.

References:
    [1] http://dictionary.reference.com/browse/light
    [2] http://en.wikipedia.org/wiki/Light
    [3] http://www.physics4kids.com/files/light_intro.html
    [4] Soriano, M., Applied Physics 187 Handouts, "Activity 2:  Familiarization with Properties of Light Sources". 2010.