Information on Spectral Irradiance Data

The radiometric data shown at the end of this section was measured in our Standards Laboratory. The wavelength calibrations are based on our spectral calibration lamps. Irradiance data from 250 to 2500 nm is based on an NIST traceable calibrated quartz tungsten halogen lamp. We validated the measurements using calibrated detectors. We used a calibrated deuterium lamp for wavelengths below ~300 nm. In both cases, we use interpolation to infer the irradiance of the calibrated lamp at other than the discrete NIST calibration wavelengths. We measured each of the lamps to be calibrated, in the most favorable orientation.

Figure 1. QTH lamps with dense flat filaments have highest irradiance along the axis normal to the filament plane through the filament center. We orient the arc lamp so the seal-off tip and, in some cases, the starter wire does not interfere with the measurement.

The lamps are operated vertically and the measurement is made in the horizontal plane through the center of the radiating filament or arc. The lamps are rotated for maximum flux at the measurement site. This is particularly important for our planar filament quartz tungsten halogen lamps. At 0.5 m the flux density of all our lamps is uniform over at least a 25 x 25 mm2 area. As you move out of the plane but still maintain the same 0.5 m distance and face the source, the recorded power should in principle fall according to Lambert’s Law for a planar source and remain constant for a point source. Measurements show something in between, with the arc lamps resembling point sources up to the electrode shadowing limit.

Figure 2. Set-up for a radiometric measurement.

As you change the measuring distance from 0.5 m, the irradiance follows the inverse square law providing the distance, d, is larger than 20 to 30 times the radiating element size. The shortest distance we use in our measurements is 300 mm.

Figure 3. Example of the spectral irradiance curves we show for our arc, quartz tungsten halogen, and deuterium lamps.

Working with Semi-Log Displays

The advantage of the semi-log display is the range our graphs cover, from very low levels to large peaks. Fig. 4 shows the linear display of the graph shownin Fig. 3. You get a much better sense of the height of the peaks, but the values at lower levels are lost.

Figure 4. Linear display of the graph shown in Fig. 3.

The logarithmic compression can be deceptive when it comes to estimating the area under a portion of the curve, to determine the total irradiance from λ₁ to λ₂, for example. You cannot rely on a rapid visual comparison unless you remember that the area at the bottom must be discounted appropriately. The peaks are much more important than they seem! So, you should calculate the area using the data values you read from the curve.

The logarithmic scale complicates estimation of the amount of irradiance in any peak. The half maximum is no longer halfway between the peak top and the bottom of the graph. You can easily find the half maximum by measuring the distance from 1 to 2, or 10 to 20, etc., on the logarithmic axis scale. Moving down this distance from the peak locates the half maximum (Fig. 5). We discuss the spectral peaks in the discussion on see Calculating Output Power

Figure 5. Calculating the FWHM from a log graph.

How Good is the Data?

We measured the irradiance data on all our lamps using both multichannel detectors with our MS257™ Spectrograph, and scanning monochromators. We used integrating spheres for most of the measurements. This effectively averages the polarization of the incoming radiation. Stress birefringence in the arc lamps and the filament structure of the lower power QTH lamps cause noticeable polarization of the output that may enhance or detract from your application.

We have a high degree of confidence in our data and cross check them with full radiant power meters and calibrated filters. The measurements are of lamps early in their life, operated in open air. Thermal conditions are different for lamps operated in lamp housings, and the spectral distribution changes slightly as the lamps age. Mercury lamps are particularly sensitive to thermal changes.

We see ±15% variation in output from lamp to lamp even within the same batch of lamps. We see substantially more variation in the UV output (

In short, we believe that this set of data is the most comprehensive and reliable you will find for lamps of this type and are an excellent resource for first estimates. But don't base a tightly toleranced system design on the data without additional characterization of the lamp in its intended operating environment.

Finding the Right Spectral Irradiance Curve

Refer to Table 1 to find the model of a lamp you are interested in. You can then click on the model for the spectral irradiance graph and additional information and specifications.

Table 1 UV-IR Radiation Sources

Model	Lamp Type	Wavelength Range	Type/Wattage
63162	Deuterium	~160 to 400 nm	30 Watt Deuterium Lamp, 1 mm Arc
63163	Deuterium	~160 to 400 nm	30 Watt Deuterium Lamp, 0.5 mm Arc
63165	Deuterium	~160 to 400 nm	30 Watt Deuterium Lamp, 0.5 mm Arc, Ozone Free
6251NS	Xenon	200 to 2500 nm	75 Watt Xenon Arc lamp
6247	Xenon	200 to 2500 nm	75 Watt Xenon, High Stability Arc Lamp
6263	Xenon	200 to 2500 nm	75 Watt Xenon Arc Lamp ( Ozone Free)
6257	Xenon	200 to 2500 nm	100 Watt Xenon, Ozone Free Arc Lamp
6255	Xenon	200 to 2500 nm	150 Watt Xenon Arc lamp (Ozone Free)
6254	Xenon	200 to 2500 nm	150 Watt Xenon, UV Enhanced Arc lamp
6256	Xenon	200 to 2500 nm	Xenon Arc Lamp, 150 W
6258	Xenon	200 to 2500 nm	300 Watt Xenon Arc lamp (Ozone Free)
6267	Xenon	200 to 2500 nm	500 Watt Xenon Short Arc Lamp, Ozone Free
6271	Xenon	200 to 2500 nm	1000 Watt Xenon Arc lamp (Ozone Free)
62711	Xenon	200 to 2500 nm	1600 Watt Xenon, Ozone Free Arc Lamp
6427	Pulsed Xenon	200 to 2500 nm	60W Flash Lamp, 5 J, 9 µs, 60Hz
6282	Mercury	200 to 2500 nm	50 Watt Mercury Lamp
6283NS	Mercury	200 to 2500 nm	200 Watt Mercury Lamp
6286	Mercury	200 to 2500 nm	350 Watt Mercury Lamp
6285	Mercury	200 to 2500 nm	500 Watt Mercury Lamp
6287	Mercury	200 to 2500 nm	1000 Watt Mercury Lamp
6291	Mercury (Xenon)	200 to 2500 nm	Hg(Xe) Arc Lamp, 200 W
6292	Mercury (Xenon)	200 to 2500 nm	200 Watt Hg(Xe) Lamp, Ozone Free
66142	Mercury (Xenon)	200 to 2500 nm	500 Watt Hg(Xe) Lamp
6293	Mercury (Xenon)	200 to 2500 nm	1000 Watt Hg(Xe) Lamp
6295NS	Mercury (Xenon)	200 to 2500 nm	1000 Watt Hg(Xe) Lamp, Ozone Free
62712	Mercury (Xenon)	200 to 2500 nm	1600 Watt Hg(Xe), Ozone Free Arc Lamp
6297	EmArc™ Enhanced Metal Arc	200 to 2500 nm	200 Watt EmArc™ Enhanced Metal Arc
6332	Quartz Tungsten Halogen	240 to 2700 nm	50 Watt Quartz Tungsten Halogen, Short Filament
6337	Quartz Tungsten Halogen	240 to 2700 nm	50 W Quartz Tungsten Halogen Lamp
6333	Quartz Tungsten Halogen	240 to 2700 nm	100 Watt Quartz Tungsten Halogen
6334NS	Quartz Tungsten Halogen	240 to 2700 nm	250 Watt Quartz Tungsten Halogen Lamp
6336	Quartz Tungsten Halogen	240 to 2700 nm	600 Watt Quartz Tungsten Halogen Lamp
6315	Quartz Tungsten Halogen	240 to 2700 nm	1000 W Quartz Tungsten Halogen
6317	Quartz Tungsten Halogen	240 to 2700 nm	1000 W, 28000 Lumens, 3200 K Color Temp.
6363	Infrared Elements	1 to 25 µm	IR Emitter, 140 W Element
6575	Infrared Elements	1 to 25 µm	Infrared Ceramic Element, 22 Watt
6580	Infrared Elements	1 to 25 µm	Low Cost Infrared Element, 9 Watt
80030	Infrared Elements	1 to 25 µm	24 W SiC Source Element

Spectral Irradiance Data

Spectral irradiance curves for our lamps and solar simulators can be found below.

Deuterium Lamps	Arc Lamps	QTH Lamps	Solar Simulators