LAB 6--Light and color
The visible spectrum is composed of all the colors of the rainbow. They are not
arranged randomly however...there is an underlying order that is based on a physical
concept called wavelength. Light behaves in a way that is similar to an ocean wave,
with crests and troughs. The distance between adjacent crests is called the wavelength.
The wavelength of visible light is very small and is measure in billionths of a meter. For
example, the approximate wavelength of green light is 550 billionths of a meter.
Because a billionth of a nanometer is such a small quantity, we have an abbreviated
name for it: we call it a nanometer.
So we say that green light has a wavelength of a billion nanometers.
The wavelength ranges for the colors of light we see are as follows:
400-440 nanometers
440-500 nanometers
500-560 nanometers
560-590 nanometers
590-610 nanometers
610-800 nanometers
violet
blue
green
yellow
orange
red
The white light we see as normal sunlight is a superpositon of all of these colors
Light above 800 nanometers is called infrared light and is invisible, and light below 400
nanometers is called ultravioet and is also invisible.
We can break light up into its component colors using a prism or a diffraction grating.
Your instructor will demonstrate the operation of both instruments. You can also select
the color you wish from white light using a colored filter, usually made from colored
glass or plastic.
When the light from a prism is shined on a screen
Not all light that is emitted is white light. Various atoms and molecules emit specific
colors of light thqat are characteristic of them.
Not all white light is composed of all colors. It is possible to make white lightusing only a
few colors of the spectrum. Some lights used in street lighting possess this property.
In todays lab you will use a variety of optical instruments to examine a variety of
phenomena in which light interacts with matter or in which light is produced by matter.
Specifically you will examine the following phenomena
I General Behavior of Light
1) The behavior of some optical instruments:
Lenses, prisms, mirrors and gratings
Examine the behavior of parallel rays of light with different kinds of mirrors and lenses.
What makes light converge and diverge?
Examine the effect of a prism on light.
2) The use of optical instruments, specifically a grating photometer
3) A chemical reaction initiated by ultraviolet light
Report on the “color beads” and the luminescent frisbees.
4) The effect of fluorescent dyes on clothing
Report on your instructor’s demonstration, commenting on the rationale for including
fluorescent dyes in detergents.
5) The use of color to delude the eye’s pereception of depth
6) How primary colors can be combined to yield other colors
Examine the color produced when you combine different colors of light.
II The chemical Signatures of elements and other substances
1) The appearance of a continuous spectrum using an ordinary incandescent lamp
2) The appearance of the spectra from fluorescent lights, the street lights in prospect
park and the orange light in the parking lot of Wilson’s Farms.
3) The spectra of discharge lamps using various gaseous elements.
4) The spectrum from a sodium discharge Lamp
5) The flame spectra for lithium, calcium, sodium and strontium
For Part 1 report qualitatively, using sketches when necessary about what you
observed.
For part 2, report numerical values for wavelengths where possible. Speculate on what
elements are responsible for the appearance of the spectra you observe for the
streetlights and for the fluorescent lights.