THORLABS SLS301 User Manual page 5

Stabilized Benchtop Halogen Light Source Chapter 3: Product Overview
Chapter 3 Product Overview
3.1. Planck's Law and Blackbody Radiation
A black body is an object that absorbs all incident electromagnetic radiation (e.g. light), no light passes through or
is reflected. However, despite the name, a black body will also emit electromagnetic radiation. The radiation of a
black body in thermal equilibrium is described by Planck's Law:
2 1
,
1
I T K
Where is the radiated power per unit area of emitting surface per unit wavelength at temperature ; is the
h c
Boltzmann constant, is the Planck constant, is the speed of light.
By measuring the spectrum of the blackbody radiation, we can calculate the temperature of this black body. Figure
3.1 shows the radiated power per unit area I as a function of wavelength at various temperatures.
Figure 3.1: Blackbody Radiation at Different Temperatures
In real life, broadband light sources may vary widely from the ideal black body in terms of the frequency and intensity
of the light emitted. By comparing the light source to an ideal black body at a given temperature, one can
characterize the light source by the temperature of the blackbody radiator which has the same chromaticity, which
is known as the color temperature of the light source.
3.2. Tungsten-Halogen Lamp
A tungsten-halogen lamp is an advanced form of an incandescent lamp. The structure of a tungsten-halogen bulb
is shown in Figure 3.2. It consists of a tungsten filament sealed in a quartz bulb envelop filled with inert gas with
traces of halogen mixed in.
During operation, a current flows through the filament, which will heat up to around 3000 K. Tungsten emits visible
and infrared light at this temperature, creating a light source that can be approximated by a blackbody radiator.
Page 3 Rev E, September 28, 2018