Ocean Optics OOIBase32 - Manual (Page 105)

A: Experiment Tutorials
Relative Irradiance Experiments
Irradiance is the amount of energy at each wavelength emitted from a radiant sample. In relative terms, it
is a comparison of the fraction of energy the sample emits and the energy the sampling system collects
from a lamp with a blackbody energy distribution (normalized to 1 at the energy maximum). OOIBase32
calculates relative irradiance with the following equation:
S λ - D λ
I λ = B λ
(
R λ - D λ
)
Where:
B
λ = Relative energy of the reference (calculated from the color temperature) at wavelength
λ
S
λ = Sample intensity at wavelength
λ
D
λ = Dark intensity at wavelength
λ
R
λ = Reference intensity at wavelength
λ
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 PC, 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.
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