Spectral irradiance measurements over the range of 200 to 1060 nm were made on a 1000-watt xenon arc lamp over a period of 1500 hours. Four sets of measurements were made after periods of 70, 525, 1000, and 1500 hours of operation. The lamp (Hanovia Compact Xenon Arc Lamp) was mounted in the NASA Solar Irradiation System. When used in the System, the lamp is used as the radiating source for six test stations. Measurements were made of both the longterm stability (or variation of spectral irradiance as a function of time) and the actual spectral irradiance incident on the test specimen

Schneider, W. E.

English

NASA Technical Reports Server

NASA CR-132533
LONG TERM SPECTRAL IRRADIANCE MEASUREMENTS
OF A 1000-WATT XENON ARC LAMP
by William E. Schneider
(NASA-CR-132533) LONG TERM SPECTRAL N74-35113)
IRRADIANCE MEASUREMENTS OF A 1000-WATT
XsNCN ARC LAMP (Optronic Labs., Inc.,
Silver Spring, Md.) 13 p HC $3.00 Unclas
CSCL 09E G3/23 51046
,Silver Spring, Maryland
Prepared under Contract No. NAS 1-13194 by
OPTRONIC LABORATORIES, INC.
Silver Spring, Maryland
for
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
https://ntrs.nasa.gov/search.jsp?R=19740027000 2020-03-23T02:44:30+00:00Z
LONG TERM SPECTRAL IRRADIANCE MEASUREMENTS
OF A 1000-WATT XENON ARC LAMP
INTRODUCTION
Spectral irradiance measurements over the range of 200 to 1060 nm were
made on a 1000-watt xenon arc lamp over a period of 1500 hours. Four
sets of measurements were made after periods of 70, 525, 1000, and
1500 hours of operation. The lamp (Hanovia Compact Xenon Arc Lamp,
Catalogue No. 976C0010) was mounted in the NASA Solar Irradiation
System. When used in the System, the lamp is used as the radiating
source for six test stations. Measurements were made of both the long-
term stability (or variation of spectral irradiance as a function of time)
and the actual spectral irradiance incident on the test specimen.
MEASUREMENT TECHNIQUE
Figure 1 shows an optical layout of the six-station Solar Irradiation Sys-
tem. Each station consists of a light-tight chamber with an adjustable
lens (L) for imaging the arc on the sample (S). Typical size for a sample
is 4. 2 cm 2 . In normal operation, a solar cell is placed in the sample
position and the lens is adjusted until a reading of one sun is obtained. The
use of a lens, however, produces an image which is quite non-uniform in
irradiance. In order to eliminate the effects of non-uniformity and,
since the positioning of the entrance port of the spectroradiometer system
at the sample plane was physically impractical, the lens was removed from
the system and the spectral irradiance was measured at a point even with
the end of the test chamber.
The irradiance at this point (without the lens in place) was fairly uniform.
The exact position of the spectroradiometer was noted and it was possible
to realign the instrument and repeat readings to within the stability toler-
ance of the lamp itself.
Upon completion of the four sets of spectral irradiance measurements, the
lens was remounted within the test chamber and adjusted in the normal
manner for a reading of one sun. A special filter-radiometer was then
positioned in the sample plane and a measurement of the irradiance at 580
nm was made.
Prior to inserting the lens, the spectral transmittance of the lens was mea-
sured by NASA Langley. Thus, from a knowledge of the spectral irradiance
(without the lens), the spectral transmittance of the lens and the irradiance
measurements made with the filter-radiometer, the spectral irradiance
over the 4. 2 cm 2 sample plane could be calculated.
TEST APPARATUS
Optical Radiation Measurement System
Measurements of spectral irradiance were made with an Optronic Labora-
tories Model 740 Optical Radiation Measurement System. The basic sys-
tem includes a rugged, high-efficiency (f/4) single grating monochromator;
a stable, ultraviolet enhanced silicon photodetector; and a low-noise elec-
tronics unit having a 3-1/2 digit display, reading directly in amperes.
The Czerny-Turner design, coupled with the stray light and second order
blocking filters, reduces the effect of stray light to less than 0. 1% for most
wavelengths, with a maximum effect at 300 nm of 2%. Fixed entrance and
exit slits (1.25 mm in width), which produce a bandpass of 5 nm, were used
over the entire 200 to 1060 nm wavelength region.
The radiation measurement system is normally calibrated in W cm - 2 nm - l
per ampere over the 300 to 1060 nm region. For measurements over the
200 to 300 nm range, the standard grating was replaced with a uv blazed
grating and the silicon detector was replaced with a solar-blind photodetec-
tor. The use of a solar blind detector, coupled with the uv grating, enabled
measurements to be made as low as 200 nm without significant stray light
effects. Figure 2 gives the spectral response of the detector.
Filter Radiometer
A specially modified filter radiometer consisting of an Optronic Labora-
tories Model 730 Radiometer/Photometer with a modified Model 85 Cosine
Receptor having a receiving area of 4. 2 cm 2 , equivalent to the sample
area, was used for the final irradiance measurements. For these mea-
surements, the diffuser was replaced with a slightly larger one having a
receiving surface equivalent to the sample area (4. 2 cm 2 ). A narrow band-
pass interference filter transmitting at 580 nm was used in conjunction with
the radiometer and cosine receptor. Figure 3 shows a diagram of the
complete detector head.
-2-
CALIBRATION PROCEDURE - SPECTRORADIOMETRIC
Calibration of the Optical Radiation Measurement System and the Filter
Radiometer was performed using a 1000-watt tungsten-halogen lamp
standard of spectral irradiance. Calibration of the lamp standard, de-
signated S-5, over the range of 250 to 1060 nm is based on the new
(1973) NBS irradiance scale. Spectral irradiance values for S-5 from
250 to 200 nm were determined through comparison to a similar lamp
previously calibrated relative to a 30000 C blackbody reference source.
The uncertainty in the calibration of standard S-5 ranges from + 3. 5%
at 250 nm to ± 1.25% in the visible and near infrared. The transfer
error to the Radiation Measurement System is on the order of 1%.
Although the uncertainty in the region below 250 nm is not precisely
known, the relative calibration is fairly accurate. Thus, any changes
in the spectral irradiance of the xenon lamp over the 1500 hour period
were accurately determined. All measurements above 250 nm were
made on an accurate absolute basis.
Although the stability of the Optical Radiation Measurement System is
extremely good, the system was completely calibrated before and after
each trip to NASA Langley. A complete calibration was performed as
follows:
1) 1000-watt standard S-5 was set up normal to and at a distance of
50 cm from the entrance slit of the spectroradiometer. A Con-
stant Current DC Power Supply was used to supply a set current
at 8. 30 amp dc to the standard. The accuracy in the operating
current is better than _ 0. 1%.
2) With the standard uv enhanced silicon detector in place, along with
the standard grating, detector output readings in amperes were
taken at 10 nm intervals over the range of 300 to 1060 nm. The
three standard second order blocking filters were inserted as
follow s:
Blocking Filter #1 300 to 350 nm
Blocking Filter #2 350 to 650 nm
Blocking Filter #3 650 to 1060 nm
3) The standard grating and detector were replaced with the uv blazed
grating and the solar blind diode. Detector signals were then re-
corded at 10 nm wavelength intervals over the 200 to 300 nm region.
A Corning 7-54 blocking filter was used over the 240 to 300 nm
region. No blocking filter was used below 240 nm.
-3-
4) The spectral responsivity of the system in Watt cm-2 nm - I per
ampere was then computed.
The above procedure was performed before and after each measurement
on the xenon lamp.
The spectral measurements on the xenon lamp were fairly straightforward.
The spectroradiometer was set up in the same manner for each of the four
sets of measurements. Detector readings were taken at 10 nm wavelength
intervals over the 200 to 1060 nm region with the proper gratings, detectors,
and filters in place. The operating voltage and current for the xenon lamp
are also recorded.
The data reduction consisted of taking the average of the calibration factors
before and after the xenon lamp measurements and multiplying these values
by the corresponding detector output when looking at the xenon lamp. In
most cases, the calibration factors for the eight calibration runs agreed to
about t 1 %. This is within the uncertainty of the standards and also within
the actual short-term stability of the xenon lamp.
CALIBRATION PROCEDURE - FILTER RADIOMETRIC
Lamp Standard S-5 was also used to calibrate the Filter Radiometer. The
filter radiometer, with the Cosine Receptor attached to the unit (Figure 3)
was positioned such that the lamp standard was normal to and at a distance
of 50 cm from the cosine receptor. The cosine receptor could easily be
removed in order to insert the narrow bandpass interference filter. The
calibration was also in units of Watt cm - 2 nm- per ampere.
-4-
RESULTS AND DISCUSSION
Table I gives the results of the spectral measurements as made
with the Optical Radiation Measurement System. Table II gives
the irradiance values and the percentage change in the lamp's
irradiance after the four sets of measurements.
As shown in Table II, there is a substantial decrease in the spectral
irradiance of this xenon lamp after 1500 hours of operation, with
most of this decrease occurring in the first 1000 hours of lamp
operation.
The purpose of the final irradiance measurement using the filter
radiometer was to determine the spectral irradiance of the NASA
Solar Irradiation System in a normal sample irradiation configuration.
The sample focusing lens was, installed and adjusted for one solar
constant at approximately 500 nm, using the NASA filtered, solar cell
detector so that these measurements could be directly compared to
published values of the solar spectrum. " This comparison is made in
Table III. Table III shows that the ultraviolet irradiance of the Solar
Irradiation System is substantially lower than the published values of
irradiance when the filtered, solar cell detector is used for calibration.
* "The Solar Constant and the Solar Spectrum Measured from a
Research Aircraft at 38, 000 Feet", NASA Goddard Space Flight
Center Report X-322-68-304 (August 1968).
-5-
TABLE I - Spectral Irradiance of Xenon Arc Lamp
with Respect to Hours of Lamp Operation
Irradiance, pW/cm 2 -nm
after
Wavelength 70 525 1000 1500
(nrm) hours hours hours hours
200 0.133 0.107 0.084 0.081
220 .84 .688 .545 .524
240 1.92 1.56 1.50 1.47
260 3.60 2.90 2.80 2.77
280 5.80 4.89 4.80 4.76
300 11.6 9.09 8.20 7.90
320 18.8 14.9 12.8 12.0
340 28.1 22.7 19.2 17.5
360 35.0 28.5 24.1 22.0
380 50.8 40.7 35.1 31.4
400 68.3 55.9 47.2 41.6
420 90.4 69.4 59.4 51.6
440 103 83.9 71.0 62.0
460 138 111 97.8 85.8
480 155 123 110 95.3
500 155 125 107 92.6
520 169 139 117 102
540 183 149 127 113
560 197 164 138 121
580 211 177 149 130
600 215 182 153 134
620 230 197 166 146
640 230 196 163 142
660 234 198 167 150
680 250 215 185 167
700 245 213 177 159
720 253 223 186 166
740 276 247 211 190
760 273 237 208 189
780 224 193 165 146
800 268 247 207 179
820 584 496 441 435
840 451 395 353 313
860 230 199 165 146
880 1018 918 925 877
900 587 554 447 410
920 873 76 701 558
940 728 698 636 563
960 333 329 256 220
980 970 941 954 910
TABLE I (continued)
Irradiance, pW/cm 2 -nm
afte r
Wavelength 70 525 1000 1500
(nm) hours hours hour s hours
1000 427 398 281 241
1020 243 241 184 155
1040 158 153 123 108
1060 160 158 129 111
TABLE II - Change in Spectral Irradiance of Xenon Arc Lamp
with Respect to Hours of Lamp Operation
IRRADIANCE, pW/cm 2 -nm i % Decrease in
after Irradiance, after
Wavelength 70 525 1000 1500 525 1000 1500
(nm) hours hours hours hours hours hours hours
200 0. 133 0. 107 0.084 0.081 20 37 39
250 2.64 2.14 2. 08 2.01 19 21 24
300 11.6 9.09 8.20 7.90 22 29 32
350 33.0 27.0 23.0 19. 5 18 30 41
400 68.3 55.9 47. 2 41.6 18 31 39
450 124 110 86. 7 75. 5 11 30 39
500 155 125 107 92. 6 19 31 40
550 189 156 133 117 17 30 38
600 215 182 153 134 15 29 38
650 236 207 171 152 12 28 36
700 245 213 177 159 13 28 35
750 268 240 203 182 10 24 32
800 268 247 207 179 8 23 33
850 219 175 151 132 20 31 40
900 587 554 447 410 6 24 30
950 689 666 635 571 3 8 17
1000 427 398 281 241 7 34 44
TABLE III
Spectral Irradiance of Xenon Lamp with Lens Adjusted
for One Sun and Solar Spectral Irradiance
Wavelength (pW/cm2 nm) Wavelength (pW/cm 2 nm)
(nm) Xenon Lamp Sun' (nm) Xenon Lamp Sun*
200 0.161 1.30 660 348 146.8
220 1.17 5.75 680 387 141.8
240 3.41 6.30
260 6.50 13.0 700 369 136.9
280 11.2 22.2 720 385 131.4
740 441 126.0
300 18.5 51.4 760 438 120
320 28.5 81.9 780 339 115
340 40.2 105
360 50.5 105.5 800 415 110.7
380 71.7 111.7 820 1009 106
840 726 101
400 93.5 143.3 860 339 97
420 115 175.8 880 2035 93
440 138 182.3
460 190 208. 900 951 88.9
480 210 208.5 920 1295 87
940 1306 84.5
500 204 194.6 960 510 81
520 225 183.3 980 2111 77.5
540 249 178.3
560 267 169.5 1000 559 74.6
580 290 170.5 1020 360 72
1040 251 69
600 303 164.6 1060 258 66
620 334 157.6
640 329 151.7
"The Solar Constant and the Solar Spectrum Measured from a Research Aircraft
at 38,000 Feet", NASA/Goddard Space Flight Center Report X-322-68-304
(August 1968).
Figure 1
Optical Layout - Solar Irradiation System
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IN TERFERENCE
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Long term spectral irradiance measurements of a 1000-watt xenon arc lamp

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