Plank's Constant & LED

From text books that the value of Planck's constant is about 6.626e-34. The LED lab provides a method for deriving planck's constant by observing the spectra of an LED through a diffraction grating.

Method:
E=eV
wavelength=hc/E
slope=experimental plank's constant

The data and plot shown below:

color	Vled	wavelength(m)	c/E(j)
Yellow	1.95	5.90E-07	9.61538E+26
Blue	2.76	4.50E-07	6.79348E+26

%error h=25.2%

CONCLUSION:

With the values of the wavelength known, we can solve for our experimental value for Planck's constant by using the formula below.

Given the conditions, Both Yellow and Blue had relatively high error. Conincidentally, their spectra also contained various colors which made it hard to pinpoint the maxima that corresponded to the color of the LED itself. This is likely due to the fact that green is not a primary color meaning it contains various other colors of the spectrum. The particular shade of yellow also had an orange tinge to it. Overall, it appears that the colors on the ends of the visible spectrum were much easier to identify. 

The reason for this could be the fact that the point "D" was chosen in a rather unscientific method of one observer directing a second person to align a pen on the D axis until it was over the perceived same wavelength of color as the LED. However the method was able to at least yield a result that is within the same order of magnitude. In the future, it would be best to know the wavelength of light that is already on the LED within a certain degree of uncertainty. I believe the majority of the error resulted from simple human lapses in judgement. Even a small value of error for D would throw off all future calculations and propagate the error through the entire experiment.