Ocean Optics S1024DW Install - Manual (Page 58)

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Relative Irradiance Experiments
Irradiance is the amount of energy at each wavelength from a radiant sample. In relative terms, it is the
fraction of energy from the sample compared to the energy collected from a lamp with a blackbody
energy distribution, normalized to 1 at the energy maximum. Relative irradiance is calculated by the
following equation:
S λ - D λ
I λ = B λ
(
R λ - D λ
)
where B
λ
is relative energy of the reference calculated from the color temperature in Kelvin, S is the
sample intensity at wavelength
λ
, D is the dark intensity at wavelength
λ
, R is the reference intensity at
wavelength
λ
.
Common applications include characterizing the light output of LEDs, incandescent lamps and other
radiant energy sources such as sunlight. Also included in irradiance measurements is fluorescence, in which
case the spectrometer measures the energy given off by materials that have been excited by light at a
shorter wavelength. To take a relative irradiance measurement:
1. Make sure you are in scope mode, by either clicking the scope mode icon on the toolbar, or selecting
Spectrum | Scope Mode from the menu. Make sure the signal is on scale. The peak intensity of the
reference signal should be about 3500 counts. The light source must be a blackbody of known color
temperature. Take the reference reading by clicking the store reference spectrum icon on the toolbar
or selecting Spectrum | Store Reference from the menu.
2. While still in scope mode, take a dark spectrum by completely blocking the light path. Take the dark
reading by clicking the store dark spectrum icon on the toolbar or selecting Spectrum | Store Dark
from the menu.
3. Take a relative irradiance measurement by first positioning the fiber at the light source you wish to
measure. Then choose the irradiance mode icon on the toolbar or select Spectrum | Relative
Irradiance Mode from the menu. In the Reference Color Temperature dialog box, enter the light
source’s color temperature in Kelvin and click OK. To save the spectrum, click the save icon on the
toolbar or select File | Save | Processed from the menu.
" " " "
If at any time any sampling variable changes -- including integration time, averaging,
boxcar smoothing, distance from light source to sample, etc. -- you must store a new
reference and dark spectrum.
A typical configuration for an irradiance experiment.