Light Experiment
Lisa Sullivan
April 21, 2004
Starting Point Activity pg 227
Elements and Colours
Purpose
To Find out if different light sources produce different spectra
Hypothesis
Lights made of certain substances will produce a different spectrum than lights made of other
substances.
Materials
Fluorescent light
Frosted incandescent light bulb
Non-frosted incandescent light bulb
Mercury vapour bulb
Argon gas discharge tube
Hydrogen gas discharge tub
Apparatuses
Hand-held spectroscope
Procedure
For each light source, aim the spectroscope at the light source and look at the rainbow-like
spectrum. Make a sketch of the spectrum and label the colours. Record wether the spectrum is
continuous or interrupted.
Observations
Fluorescent Light (in science room, three from back, two from right [facing front])
Colour: Yellow
Spectra Type: Interrupted
Frosted incandescent light bulb (7.5 volt)*
Colour: Yellow
Spectra Type: Continuous
Unfrosted incandescent light bulb (12 volt)*
Colour: Yellow
Spectra Type: Continuous
*The only difference between these two is that the unfrosted one is brighter
Mercury vapour bulb
Colour: Blue
Spectra Type: Interrupted
Argon gas discharge tube
Colour: Purple-Red-Purple
Spectra Type: Continuous
Hydrogen gas discharge tube
Colour: Blue-Purple-Blue
Spectra Type: Interrupted
What Did You Discover?
1. The frosted and unfrosted incandescent light bulbs gave the most complete spectra. The other
ones might be more interrupted because they do not contain as many substances as the
incandescent bulbs do.
2.a. The colours in the fluorescent light are : purple, dark green, light green, orange, and red. You
know these are the colours because they are the colours that you saw in the spectroscope.
2.b. When you saw the light I observed without a spectroscope, it looked yellow, but other lights
may have had a different colour because they had more of a certain substance.
3. Different light sources each have their own individual spectra, therefore an ordinary lightbulb will have a different spectra the street light will
Conclusion
The experiment proved my hypothesis to be correct, the type of substance that you have in
a light will determine what it's spectrum will be, no substances have the same spectrum. Spectra
can vary from being continuous with lots of different colours to being interrupted with few
colours. For example, Incandescent lights have continuous spectra with purple, blue, dark green,
light green, yellow, orange, and red. The hydrogen gas discharge has an interrupted spectra with
only two colours, red, and yellow. But, some continuous spectra do not have a lot of colours. Thehydrogen discharge tube, for example, only has three colours, purple, green, and red. The numberof colours in the interrupted spectra is not always just a few. Fluorescent light, for example has five different colours, purple, dark green, light green, orange and red. The black spaces in interrupted spectra can also range from being very big, like in the mercury vapour bulb, to very small, like in the fluorescent light.
