Instrumentation & Measurement Magazine 26-3 - 54

Data Description
Wavelengths λi
CIEi
weights
Relative Spectral
Irradiance (RSIi
Δλi
SI lumens/watt
Lux Measurement
)
Table 1 - Data required for calculations
Units / Comments
Wavelengths λi
in nm of each data point in the light range
CIE Photopic Luminosity Function values for each wavelength λi
typically requires interpolation.
in per unit value of 0 to 1.0. This
Relative Spectral Irradiance of the light source in units of 1/nm for each wavelength λi
range of 0 to 1.0. Values are obtained by either a measurement or from the datasheet.
in the
The Δλi is the distance between two adjacent samples. Δλi in nm enables the conversion from
relative spectral illuminance in 1/nm to relative illuminance in per unit.
683 lumens/watt conversion factor
Lux (Ev) reading of light source, with meter calibration matching the CIEi
Table 2 - LED light sources
LED Light
GE 4US7, 450 lumens, 5000 K
Utilitech, E359760, 600 lumens, 3000 K
GE 9A19, 800 lumens, 2700 K
Bolder Cree XM-L2 LED
Comment
Standard Edison base LED light bulb with clear glass enclosure
Standard Edison base LED miniature-sized light bulb with frosted plastic
enclosure
Standard Edison base LED light bulb with frosted plastic enclosure
LED battery-powered flashlight with known LED. Unlike the bulbs with constant
output, because of thermal effects, as the flashlight runs, the light output drops
incident angle of the light. An IoT device mounted on a wall receives
less illuminance than a device mounted directly under
a light source.
Data Required for Calculation
Table 1 summarizes the inputs required for this conversion
method. For consistency, the wavelengths utilized were nanometers
(nm).
Practical Calculations
All the data provided, interpolated, or measured were discrete
values. Discrete data means that the calculations are performed
by summations instead of integrations. For the summations, frsi
is replaced by RSIi
, fCIE
with CIEi
:
priate data collection and interpolation, (6) calculates the Pd
power density factor in W/m2
i max
P E( / )(1 / RSI  CIE )

d vw
L
i1
Once Pd is calculated, (7) expresses the irradiance of the artificial
light source:
i max
   i
d
i
IP RSI 
i1
Laboratory Confirmation
The first laboratory confirmation of the conversion of illuminance
measurements to irradiance utilized a PMA2100
irradiance meter with a PMA2140L low-level sensor head. The
results showed a significant mismatch between the measurements
and theoretical calculations. The poor results led to the
54
(7)
i
i
i
(6)
, and d with i . With approinvestigation
of PV measurement applications with non-solar
spectra light. The authors in conclude that irradiance measurements
from non-uniform spectra are problematic. Recent work
on the performance of solar cells under artificial light shows
the importance of spectral mismatch [8]. In addition, technical
discussions with an irradiance meter vendor confirmed that
silicon-based sensors, with their inherent non-linear measurement,
are calibrated specifically for spectra close to AM1.5G.
Because of this issue, laboratory confirmation used the spectra
independent Apogee SP-510 thermopile-based sensor.
Light Sources
The measurement recorded illuminance and RSI from a sample
of LED light sources. Table 2 summarizes the light source
information, and Fig. 3 is a photograph of the light sources.
per unit weights.
Fig. 3. LED Light Sources, order left to right are: GE 4US7; Utilitech E359760;
GE 9A19; and Bolder Cree XM-L2 LED.
IEEE Instrumentation & Measurement Magazine
May 2023

Instrumentation & Measurement Magazine 26-3

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 26-3