Ocean Optics SpectraSuite - Manual (Page 166)

A: Experiment Tutorials
154 000-20000-300-02- 201110
Where:
B

= Relative energy of the reference (calculated from the color temperature) at wavelength 
S

= Sample intensity at wavelength 
D

= Dark intensity at wavelength 
R

= Reference intensity at wavelength 
Typical relative irradiance setup: Use a light source with a known color temperature (such as the LS-1 or
LS-1-LL (lower right) to take a reference spectrum. The light to measure (lower left) accumulates through
a CC-3 Cosine Corrector (or FOIS integrating sphere) into an input fiber, which carries the light
information to the spectrometer. The spectrometer then transmits the information to the computer, which
compares the measured spectra against the reference spectrum, thus removing wavelength-dependent
instrument response from the measurement.
Common applications include characterizing the light output of LEDs, incandescent lamps, and other
radiant energy sources such as sunlight. Relative irradiance measurements also include fluorescence
measurements, which measure the energy given off by materials excited by light at shorter wavelengths
(see
Fluorescence ).
Absolute Irradiance
Absolute Irradiance uses a lamp of known output (in terms of microwatts per square centimeter per
nanometer) to calibrate the spectrometer's response at every pixel. This corrects the shape and magnitude
of the spectrum, and the resulting spectrum is in terms of microwatts per square centimeter per nanometer
(uWatt/cm
2 /nm). Note that if an integrating sphere is used, then the resulting spectrum is radiant flux , in
units of microwatts per nanometer (uWatt/nm).
To conduct an absolute irradiance measurement, it is necessary to have the following:
S : Sample spectrum (counts per nanometer)
D : Dark spectrum (counts per nanometer, with the same integration time, corrections, and
smoothing as sample)
C : Calibration (micro-Joules per count)
T : Integration time (seconds)