What does the spectrum of a light-emitting diode (LED) look like?

Principle

Care is to be taken in particular that the experimental setup is not shifted during the experiment, in particular the ruler because otherwise no reference point for the comparison of the measuring curves is available. Furthermore, this experiment has to be carried out in a completely dark room.

Benefits

• Specified for the requirements of the german final secondary-school examinations
• Especially for secondary schools
• Quantum and wave optics in a student experiment

Tasks

What does the spectrum of a light emitting diode look like?

When we observe the white LED through a grating we can see colour components across nearly the entire spectrum. Because our eye cannot see the individual frequencies objectively but overemphasises the green range it is difficult to say which intensities the individual colour ranges have. An absolute comparative determination of intensity is hardly possible.
 
In contrast to our eye, the light sensor in the set measures the light intensity very precisely and outputs a voltage proportional to the incident intensity which can be measured with the multimeter. This allows the spectrum to be measured and to determine at which frequencies the individual LEDs have their radiation maximum and what their relationship to each other is.
 
In this experiment you will learn how to (objectively) measure the spectrum.