Introduction to Infrared Elements and Output Sources

Although many sources emit some degree of infrared radiation, only a few simple economical sources can yield adequate radiant output and spectral uniformity to be workable in IR instruments.

Oriel Instruments offers five IR elements, which can be used over a broad spectral range, from 1 to 25µm (Figure 1).

Spectral irradiance of 6334 250 W QTH Lamp, and IR Elements

Figure 1. Spectral irradiance of 6334 250 W QTH Lamp, and IR Elements

Oriel Instruments’ IR Elements

The following are the five IR elements offered by Oriel Instruments:

  • 6363 Infrared Emitter has large radiating area with uniform emissivity
  • 6575 Ceramic Element is similar to Nernst element, with high irradiance
  • 6581 Miniature IR Element is efficient, radiating only in a small useful area. Long sliver matches monochromator slit geometry
  • 6580 Low Cost IR Element is the most economical IR source. It is small with efficient radiating area
  • 80007 SiC Element is a complete system, including 3.8 x 5mm SiC element in housing with electronics

Figure 2 shows 6363, 6575, 6580 and 6581 Infared Elements. The lifetimes vary considerably from element to element.

6363, 6575, 6580 and 6581 Infared Elements

Figure 2. 6363, 6575, 6580 and 6581 Infared Elements

Selection Factors of Suitable IR Source

Several factors need to be considered in the selection and comparison of IR sources:

Color temperature – The shape of the emissivity curve for a specific element affects spectral radiance or irradiance and color temperature is obtained from the convolution of the operating temperature and emissivity curve.

Operating temperature – Each source has its own operating temperature range, which allows for a realistic output and lifetime.

Radiating Area – IR emitters with larger area are advantageous for irradiance of large targets. Smaller sources, especially the 6581 Miniature IR Element is recommended for smaller targets such as a monochromator slit.

Operating Temperature and Color Temperature

The increase in the operating temperature of the source element increases both spectral radiance and irradiance, but decreases its lifetime. Hence, care must be taken to select an element with a reasonable lifetime at the operating temperature of interest.

The color temperature of a source is generally expressed by the temperature of a blackbody which would emit similar spectral radiance or irradiance. This functions properly if the source’s emissivity is spectrally flat, but becomes more complex when it has a shape similar to that of 6575 Ceramic Element. Figure 3 depicts color temperature vs wattage of 6363 IR Emitter and Figure 4 delineates Color temperature vs wattage of 6575 Ceramic element.

Color temperature vs wattage of 6363 IR Emitter

Figure 3. Color temperature vs wattage of 6363 IR Emitter

Color temperature vs wattage of 6575 Ceramic element

Figure 4. Color temperature vs wattage of 6575 Ceramic element

Oriel Instruments defines the color temperature of its sources by taking a flat section of their specific emissivity curve and fitting the black body equations to that section of their irradiance curve. The color temperature estimated using the aforementioned procedure must not be utilized for any Photometric calculations, meaning that it must not substitute for appearance associated with Coordinated Color Temperature, which is subject to more complex algorithm.

Radiating Area and Emissivity

An infrared element’s radiating area represents the region that reaches the color temperature specified for the element and is generally in the center of the element. Radiating area and total area are specified for Oriel Instruments’ sources. The Black Body equations can fully describe a perfect thermal radiator. Conversely, real thermal radiators are capable of only approximating black body performance. The emissivity curve shows the departure from the black body standard (Figures 5, 6, and 7).

Emissivity of 6363 IR Element

Figure 5. Emissivity of 6363 IR Element

Emissivity of 6575 Ceramic Element

Figure 6. Emissivity of 6575 Ceramic Element

Emissivity of 6580 and 6581 IR Elements

Figure 7. Emissivity of 6580 and 6581 IR Elements

Conclusion

Commercial Black Bodies can achieve almost unity emissivity through special cavity designs. Nevertheless, they are large and costly. Infrared elements and QTH lamps show substantial emissivity departures from unity. They are user friendly and less expensive. Irradiance from a specific element can be estimated using source size, color temperature curves, and emissivity curves.

About Oriel Instruments

Oriel Instruments, a Newport Corporation brand, was founded in 1969 and quickly gained a reputation as an innovative supplier of products for the making and measuring of light. Today, the Oriel brand represents leading instruments, such as light sources covering a broad range from UV to IR, pulsed or continuous, and low to high power.

Oriel also offers monochromators and spectrographs as well as flexible FT-IR spectrometers, which make it easy for users across many industries to build instruments for specific applications. Oriel is also a leader in the area of Photovoltaics with its offering of solar simulators that allow you to simulate hours of solar radiation in minutes. Oriel continues to bring innovative products and solutions to Newport customers around the world.

This information has been sourced, reviewed and adapted from materials provided by Oriel Instruments.

For more information on this source, please visit Oriel Instruments.

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