Comparing Spectra of Tungsten and Energy- Saving Light Bulbs

Comparing Spectra of Tungsten and Energy- Saving Light Bulbs

Purpose

Compare the spectrum of an energy-saving light bulb with that of a tungsten-filament light bulb by meanings of wavelength measurements and observational techniques.

Equipment and Materials

Shoe Box

Lamp

Tungsten-filament light bulb

Mercury vapor; energy saving light bulb

300 and/or 1000 diffraction grating

Scissors

Modeling Clay

Dark thread

Sewing pin

Drawing pin

Electrical tape

Protractor

Flashlight

Procedure

1. A fairly dark location was obtained for the conduction of the experiment. This was a room without windows (hallway and bathroom).

2. The light box was then prepared. This was done by cutting off one end of a shoe box and cutting a 1mm wide slit 5 cm long on the other side. This box was then taped to a table and covered with a light, non-synthetic towel to minimize light pollution.

3. The protractor was placed approximately 55 cm directly in front of the shoe- box; with its zero degree point of the protractor aligned with the slit of the box. A drawing pin was inserting through its apex, with its sharp point exposed.

4. The diffraction plating was placed parallel to the flat edge of the protractor and was secured upright with modeling clay. The diffraction plate was centrally aligned with the slit of the shoe- box and the tip of the drawing pin.

5. Black thread was attached to the drawing pin and a piece of modeling clay, which held a sewing pin. This served as the sighting mechanism.

6. A lamp with an energy-saving bulb was then inserted into the shoe -box and was turned on. Once observations and recordings were taken, the tungsten-filament bulb was inserted to compare qualitatively the differences between the two bulb-type’s spectra.

Data

1000 Gradient

Observation Table

	1000 Gradient
Order	Sin(Degrees)	Degrees	Wavelength
Blue Spectral Line			445 nm
1	0.446	26.5
1	0.446	26.5
2	0.876	61.2
2	0.906	64.9
3
4
5
Green Spectral Line
1	0.581	35.5
1	0.566	34.5
2
3
4
5
Red Spectral Line
1	0.67	42.1
1	0.64	39.8
2
3
4
5

Observation Table

	300 Gradient
Order	Sin(Degrees)	Degrees	Wavelength	Wavelength with Zeros for Missing Orders
Blue Spectral Line			533.13 nm	465 nm
1	0.131	7.5
2	0.272	15.8
3		No Blue
4		No Blue
5	0.766	50
Green Spectral Line			533.47 nm	589 nm
1	0.158	9.1
2	0.335	19.6
3	0.483	28.9
4		No Green
5	0.804	53.6
Red Spectral Line			692 nm	692 nm
1	0.206	11.9
2	0.376	22.1
3	0.52	31.3
4	0.728	46.7
5	0.909	65.3

Discussion/ Conclusions

Observations and data were taken after the equipment was set up. The first set of data was taken with the 1000 gradient. With the 1000 gradient, the blue spectra line produced two orders (26.5 and 64.9 degrees; 26.5 and 61.5). The green spectral line was only seen with one order (35.5; 34.50 degrees) and the red spectral line was only seen with one order (42.1; 39.8 degrees). The measurements for the 1000 gradient was taken twice; once from each side of the spectra (once from the right, once from the left). It was predicted that the degree measurement for a specific order from a specific color line would be the same from both the right and left side orders. As the data represents, the degree measurements from the left and right sides are very similar, with the largest difference being 3.7 degrees (blue spectral line, second order). This is most likely because the second order was blurry and not distinct.

The second set of data was taken with the 300 gradient. The 300 gradient produced more distinct, clear and bright color orders. The blue spectral line produced five orders, although the third and fourth orders were not distinct enough for measurements. The green spectral line also produced five orders, while the fourth order was not distinct enough to take measurements. The red spectral produced five vivid orders of color lines.

After the data was taken, the sin of the degrees measured were calculated. As implied by the graphs, with the 300 gradient, the sin (degrees) increased as the order number increased. This was true for all of the spectral lines that contained more than one order. In general, the slopes increased from blue, to green, to red; although the slope differences between the blue and green data was minute. This increase correlates to the increases in standard wavelengths from blue, to green, to red.

The second part of this experiment was performed with a tungsten- filament light bulb as compared to the energy-saving bulb that was used previously. With the tungsten-filament light bulb the orders were much different in appearance than the energy-saving light bulb. The tungsten-filament light bulb produced two full orders of diffraction and one partial order up to blue. These orders were very blurry and fuzzy. They were very non-distinct and had a grayish haze over the colors. The colors in the energy-saving light bulb were significantly more distinct and there were more orders observable.

Measurement uncertainties arose for the higher orders. This was due to the degradation of order clarity within the spectrum as the higher orders were reached. These measurements could be improved upon by using a diffraction gradient of a larger size. This would allow the higher orders to be clearer at less tangential viewing angles. Copious amounts of data and measurements would further the validity of this experiment.

Our calculated wavelengths with the 300 gradient deviated approximately 30-60 nm from the accepted wavelength values. This is most likely due to the light bulb or the specific condition that surrounded the experiment. Additionally, the 300 gradient diffraction plate had a slight diagonal crack, which may have slightly altered the results.