The author was with the National Bureau of Standards when this work was done; he is now with Optronics Laboratories, 7676 Fenton St., Silver Spring, Md. This work was supported by NASA.
A new high-intensity standard of total and spectral irradiance has been developed recently at the National Bureau of Standards. The standard consists of a 1000-W tungsten–halogen lamp mounted in a ceramic reflector, the reflecting surface of which is coated with flame-sprayed Al2O3. The lamp–reflector combination results in a source having a relatively small (3 cm × 5 cm) radiating area yielding a total irradiance, at a distance of 40 cm, of about 136 mW cm−2. The total irradiance calibrations are based on the radiance of a 1400-K blackbody and have an estimated maximum systematic error of 0.9% and a maximum estimated standard error of 0.19%. The spectral measurements were made over the wavelength range of 0.3 μm to 2.5 μm relative to the NBS 1000-W tungsten–halogen irradiance standards. The estimated uncertainty in these measurements ranges from 4% in the visible and near ir to 8% in the uv.
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Relative Spectral and Total Irradiance Ratios for a Clear 1000-W Lamp in a Silica Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Time
Time (h)
0
6
10
17
35
40
λ (μm)
0.270
1.13
1.11
1.09
0.108
1.04
1.00
0.300
1.20
1.17
1.15
1.13
1.08
1.05
0.350
1.31
1.28
1.26
1.25
1.19
1.17
0.400
1.54
1.50
1.48
1.47
1.40
1.38
0.500
1.81
1.77
1.75
1.74
1.67
1.65
0.550
1.88
1.85
1.84
1.83
1.76
1.74
0.600
1.94
1.91
1.90
1.90
1.83
1.82
0.700
2.02
2.00
2.00
1.99
1.95
1.94
0.750
2.04
2.02
2.03
2.03
1.99
1.98
1.0
2.05
2.05
2.05
2.05
2.02
2.02
1.5
2.05
2.08
2.08
2.08
2.07
2.07
2.0
2.08
2.10
2.09
2.09
2.08
2.08
2.5
2.16
2.16
2.14
2.16
2.12
2.12
Total
1.981
1.961
1.974
1.964
1.955
1.939
Table II
Relative Spectral and Total Irradiance Ratios for a Clear 1000-W Lamp in an Al2O3 Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Timea
Time (h)
2
6
25
31
54
61
82
87
110
117
λ (μm)
0.2537
0.950
0.930
0.893
0.899
0.903
0.898
0.906
0.905
0.914
0.91
0.300
0.930
0.903
0.869
0.870
0.870
0.871
0.875
0.875
0.874
0.87
0.500
1.53
1.52
1.50
1.50
1.50
1.50
1.51
1.51
1.50
1.51
0.700
1.61
1.61
1.61
1.61
1.61
1.61
1.61
1.62
1.61
1.62
1.00
1.60
1.60
1.61
1.60
1.62
1.63
1.62
1.61
1.62
1.63
1.50
1.61
1.62
1.63
1.62
1.64
1.65
1.64
1.64
1.64
1.65
Total
1.627
1.631
1.635
1.633
1.644
1.645
1.636
1.640
1.639
1.64
Standard deviation of the total for the times shown above from 25 h to 117 h = 0.27%.
Table III
Relative Spectral and Total Irradiance Ratios for a Frosted 1000-W Lamp in an Al2O3 Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Timea
Time (h)
25
47
72
80
104
127
135
λ (μm)
0.270
0.591
0.582
0.578
0.579
0.571
0.576
0.581
0.300
0.696
0.685
0.680
0.678
0.675
0.677
0.682
0.350
0.884
0.873
0.870
0.867
0.863
0.863
0.868
0.400
1.15
1.13
1.13
1.13
1.13
1.13
1.13
0.500
1.52
1.51
1.51
1.51
1.51
1.51
1.52
0.550
1.60
1.60
1.60
1.60
1.60
1.60
1.61
0.600
1.69
1.69
1.69
1.68
1.69
1.69
1.69
0.700
1.76
1.76
1.75
1.76
1.76
1.76
1.77
0.750
1.79
1.79
1.78
1.79
1.79
1.80
1.80
1.0
1.82
1.83
1.82
1.82
1.83
1.83
1.84
1.5
1.87
1.88
1.88
1.88
1.90
1.90
1.90
2.0
1.89
1.89
1.90
1.89
1.92
1.91
1.92
2.5
1.88
1.89
1.90
1.90
1.92
1.91
1.92
Total
1.720
1.720
1.723
1.718
1.725
1.727
1.725
Standard deviation of the total for the times shown above from 25 h to 75 h = 0.20%.
Total Irradiance of High-Intensity Units in mW cm−2 at a Distance of 40 cm
Unit no.
Total irradiance
T-1
145.6 mW · cm−2
T-3
141.0
T-4
149.2
T-5
143.9
T-6
138.5
T-7
138.3
T-8
134.1
T-9
138.6
Table VII
Summary of Estimated Systematic Errors and Precision in Total Irradiance Measurements
Source of systematic error
Percentage
Measurement of blackbody temperature on ipts
±0.15
Conversion of temperature to tkts
0.15
Measurement of thermocouple emf
0.05
Quality of blackbody
0.1
Distance measurement (blackbody)
0.07
Distance measurement (high intensity unit)
0.05
Area of blackbody aperture
0.15
Atmospheric absorption
0.1
Sector disk calibration
0.1
Setting of current
0.004
Estimated maximum systematic error
0.92%
Maximum estimated standard error of the eight reported calibrations
0.19%
Tables (7)
Table I
Relative Spectral and Total Irradiance Ratios for a Clear 1000-W Lamp in a Silica Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Time
Time (h)
0
6
10
17
35
40
λ (μm)
0.270
1.13
1.11
1.09
0.108
1.04
1.00
0.300
1.20
1.17
1.15
1.13
1.08
1.05
0.350
1.31
1.28
1.26
1.25
1.19
1.17
0.400
1.54
1.50
1.48
1.47
1.40
1.38
0.500
1.81
1.77
1.75
1.74
1.67
1.65
0.550
1.88
1.85
1.84
1.83
1.76
1.74
0.600
1.94
1.91
1.90
1.90
1.83
1.82
0.700
2.02
2.00
2.00
1.99
1.95
1.94
0.750
2.04
2.02
2.03
2.03
1.99
1.98
1.0
2.05
2.05
2.05
2.05
2.02
2.02
1.5
2.05
2.08
2.08
2.08
2.07
2.07
2.0
2.08
2.10
2.09
2.09
2.08
2.08
2.5
2.16
2.16
2.14
2.16
2.12
2.12
Total
1.981
1.961
1.974
1.964
1.955
1.939
Table II
Relative Spectral and Total Irradiance Ratios for a Clear 1000-W Lamp in an Al2O3 Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Timea
Time (h)
2
6
25
31
54
61
82
87
110
117
λ (μm)
0.2537
0.950
0.930
0.893
0.899
0.903
0.898
0.906
0.905
0.914
0.91
0.300
0.930
0.903
0.869
0.870
0.870
0.871
0.875
0.875
0.874
0.87
0.500
1.53
1.52
1.50
1.50
1.50
1.50
1.51
1.51
1.50
1.51
0.700
1.61
1.61
1.61
1.61
1.61
1.61
1.61
1.62
1.61
1.62
1.00
1.60
1.60
1.61
1.60
1.62
1.63
1.62
1.61
1.62
1.63
1.50
1.61
1.62
1.63
1.62
1.64
1.65
1.64
1.64
1.64
1.65
Total
1.627
1.631
1.635
1.633
1.644
1.645
1.636
1.640
1.639
1.64
Standard deviation of the total for the times shown above from 25 h to 117 h = 0.27%.
Table III
Relative Spectral and Total Irradiance Ratios for a Frosted 1000-W Lamp in an Al2O3 Coated Reflector at 150 cm vs a 1000-W Reference Source at 75 cm as a Function of Timea
Time (h)
25
47
72
80
104
127
135
λ (μm)
0.270
0.591
0.582
0.578
0.579
0.571
0.576
0.581
0.300
0.696
0.685
0.680
0.678
0.675
0.677
0.682
0.350
0.884
0.873
0.870
0.867
0.863
0.863
0.868
0.400
1.15
1.13
1.13
1.13
1.13
1.13
1.13
0.500
1.52
1.51
1.51
1.51
1.51
1.51
1.52
0.550
1.60
1.60
1.60
1.60
1.60
1.60
1.61
0.600
1.69
1.69
1.69
1.68
1.69
1.69
1.69
0.700
1.76
1.76
1.75
1.76
1.76
1.76
1.77
0.750
1.79
1.79
1.78
1.79
1.79
1.80
1.80
1.0
1.82
1.83
1.82
1.82
1.83
1.83
1.84
1.5
1.87
1.88
1.88
1.88
1.90
1.90
1.90
2.0
1.89
1.89
1.90
1.89
1.92
1.91
1.92
2.5
1.88
1.89
1.90
1.90
1.92
1.91
1.92
Total
1.720
1.720
1.723
1.718
1.725
1.727
1.725
Standard deviation of the total for the times shown above from 25 h to 75 h = 0.20%.