Technical Notes

Reliable spectroradiometry takes a lifetime of work and attention to master. Unreliable spectroradiometry is much easier to accomplish1 all it takes is missing a single critical point, like the interdependence of source time variation and detection system bandwidth or the source spectral bandwidth and instrument chromatic properties.

An FT-IR Spectrometer is an instrument which acquires broadband NIR to FIR spectra. Unlike a dispersive instrument, i.e. grating monochromator or spectrograph, FT-IR Spectrometers collect all wavelengths simultaneously. This feature is called the Multiplex or Felgett Advantage.

Oriel® Solar Simulators provide the closest spectral match to solar spectra available from any artificial source. The match is not exact, but better than needed for many applications. For the closest match possible, choose a Oriel Sol3A Class AAA Solar Simulator, these maintain an extremely tight uniformity, output stability and spectral match, as required by the photovoltaic cell manufacturers for testing PV cells.

A solar simulator is a light source that approximates the illumination of natural sunlight. The ability of a solar simulator to approximate natural sunlight is based on three criteria: (1) spectral match, (2) spatial non-uniformity of irradiance and (3) temporal instability.

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.

There are many systems of units for optical radiation. In this tutorial, we try to adhere to the internationally agreed CIE system. The CIE system fits well with the SI system of units. We work mostly with the units familiar to those working in the UV to near IR.

Spectral irradiance data is shown below for our Arc Lamps. You can click on the curve for a larger image, or on a model number for complete information on a specific arc lamp. Spectral irradiance curves for other types of lamps can be found on the right.

In a typical photo-research system, a detector measures the radiant intensity used to evoke photo-response in a sample or the radiant intensity produced by the sample in response to light or other simulation. The measurement is very frequently done after the beam has been separated into its component wavelengths.

The most accurate and economical method of wavelength calibration is the spectral calibration lamp. We offer lamps to cover wavelengths from below 185 nm to over 2.5 µm. Be sure to check out our popular battery powered Hg(Ar) calibration lamp, for the utmost in ease of use and portability.

This glossary briefly defines the terms and units most frequently used in technical discussions around solar simulation.

The spectral irradiance at any wavelength, Eλ, is in units of watts per square meter per nm (W m-2 nm-1). The value is a measure of the flux per nm at the specified wavelength incident normally onto an element of the surface divided by the area of the surface element in square meters.

Newport's PZA Ultra-High Resolution Actuator provides 12.5 mm travel with 50 N load capacity.

Here we describe our spectral irradiance curves. Again, we caution you on the need for testing of the final configuration particularly when the “total radiation budget” for the system, source to detector, is tight.

These discontinued products are no longer sold by Oriel, but are typically supported for three years from the date on which they were discontinued. Repairs and calibrations are available through Oriel Customer Service.

Below is a list of Oriel's standard families of fiber optic cables and liquid light guides, and the appropriate adapters to couple them to Oriel® Instruments MS257™ 1/4 m Monochromator and Imaging Spectrographs. Adapters for 3rd party fibers are also available.

Spectral irradiance data is shown below for our Solar Simulators. You can click on the curve for a larger image, or on a model number for complete information on a specific solar simulator.

To simplify visual comparison of our simulators' curve shapes with the shapes of the standard solar spectra curves, we scale the measured simulator output, without changing the shape.

With a spectrograph, the term bandpass refers to the entire wavelength range in the long strip output to the detector. Thus the bandpass in a spectrograph is very wide, limited only by the output aperture. However, it is not enough to simply remove the slit from a monochromator and use this larger aperture.

The constantly improving technology of detectors and wide selection of materials and detection methods allows most light detection needs to be satisfied by fairly simple systems. At the same time, with so many choices, selecting the best system can be confusing.

Spectral irradiance data is shown below for our QTH lamps. You can click on the curve for a larger image, or on a model number for complete information on a specific QTH lamp. Spectral irradiance curves for other types of lamps can be found on the right.