Color and hydrogen spectrum

This lab uses a diffraction grating to analyze wavelengths of light from a specific light source.
Our setup was as shown.

We placed a light source at the origin of the 2 rulers, placed a diffraction grating at a distance from the bulb, and looked through it and measured the range of wavelengths.We use the following formula:

where λ is the wavelength, d is the slit spacing on the diffraction grating, D is the observed horizontal distance from the light source to the band of light, L is the distance from the diffraction grating to the light.
 We took readings at 2 distances to minimize error.

L (m)	Red(D)	Violet (D)
1.5	0.65	0.3
1.8	0.745	0.35

We were then given a gas discharge tube, and our job was to determine what type of gas was in the tube based on the spectral lines we observe.

We compared the spectral bands with a chart of different gasses' spectral lines, and they corresponded almost perfectly with mercury.

color	D (m)	Measured λ	Theoretical λ
Red	0.75	690	690
Yellow	0.61	589	580
Green	0.54	535	545
Violet	0.42	439	435

We plot the measured values against the theoretical values to get a correction value of 75 nm.
We were then given a hydrogen discharge tube, and measured the spectral lines of hydrogen.

D (m) λ (Measured) (nm) λ (Calculated) (nm) λ (Theoretical) (nm) Red (D) 0.7 655 654 656 Blue (D) 0.49 495 495 486 Violet (D) 0.43 447 446 434

The different spectral lines indicate the different energy levels that the hydrogen can transition between. For each of these transitions, the hydrogen emits a photon corresponding to a specific wavelength. This method can be used to analyze an unknown gas and determine it's composition based on the energy levels.