Calculating the Output Power of a Light Source

The power in the collimated beams can be estimated at any wavelength or in any wavelength range using Oriel Instruments’ Series Q or Research Lamp Housings with any of its quartz tungsten halogen, CW and pulsed arc, or deuterium lamps. The method is the same as for calculating the output from the Monochromator Illuminators and PhotoMax™, but users need to factor in the reflectance of the ellipsoid.

At a Single Wavelength

To compute the total output power per nm at any wavelength for any of Oriel Instruments’ Lamp Housings, users need to get the irradiance value from the curve for the lamp that will be in mW m-2 nm-1. From Tables 1 and 2, users need to determine the conversion factor for their Lamp Housing and condenser type, and multiply this by the value from 1. The resulting value will be in mW nm-1. The resulting value needs to be multiplied by 1.6 when a rear reflector is utilized.

Table 1. Conversion Factors for Series Q and 250 and 500 W Research Housings

Condenser Type Spectral Range Condenser Aperture (mm) Conversion Factor*
F/# Lens Material
F/1.5 Fused Silica 200 - 2500 33 0.05
F/1 Fused Silica 200 - 2500 33 0.08
F/0.85 Pyrex® 350 - 2000 33 0.10
F/0.7 Glass/Fused Silica 350 - 2000 69 0.14
F/0.7 Fused Silica 200 - 2500 69 0.14

* Measured at 500 nm

Table 2. Conversion Factors for 1000 W Research Housings

Condenser Type Spectral Range Condenser Aperture (mm) Conversion Factor
F/# Lens Material
F/1 Fused Silica 200 - 2500 48 0.12
F/0.7 Glass/Fused Silica 350 - 2000 69 0.2
F/0.7 Fused Silica 200 - 2500 69 0.2

Total Power in a Specified Spectral Range

Finding the curve for the specific lamp is the first step in the computation of the total output power in a wavelength range. Then, the total irradiance is calculated in users’ wavelength interval, λ1 and λ2, from the graph. The total irradiance is the region under the curve from λ1 to λ2 in mW m-2. Then the total irradiance in mW m-2 is multiplied by the conversion factor corresponding to Oriel Lamp Housing and condenser. The resulting value will be in mW. The result needs to be multiplied by 1.6 if a rear reflector is utilized.

Monochromator Illuminator and PhotoMax™

The conversion factors for the PhotoMax™ and 7340 and 7341 Monochromator Illuminators at 500nm are listed in Tables 3 and 4. The conversion factors from the tables need to be multiplied by the reflectance at the wavelength of interest and divided by the reflectance at 500nm. If window is used in the PhotoMax™, the conversion factor needs to be multiplied by 0.92.

Table 3. Conversion Factors for Photomax™, at 500nm

Reflector F/# Reflector Coating Approximate Spot Size (mm) Conversion Factor
4.4 Rhodium or AIMgF2 5.2 G.8
3.7 Rhodium or AIMgF2 4.6 G.9
2 Rhodium or AIMgF2 3.G 1.1

Table 4. Conversion Factor for Monochromator Illuminator, at 500nm

Output F/# Reflector Coating Magnification Conversion Factor
3.75 AIMgF2 1.75 0.038

Pulsed Sources

Since no calibrated pulsed light standards are available from NIST, the calibrated spectra are derived from Oriel Instruments’ Lamps. Although it is basically a simple procedure, it needs extreme care like all accurate spectroradiometry. Oriel Instruments used spectral calibration lamps and calibrated UV and VIS/IR standard lamps for calibrating the spectral responsivity of its Insta-Spec™/MS257™ based spectroradiometer system.

For that purpose, an exposure time is selected that provides several thousand counts with the calibration and pulsed lamps to position the lamps to ascertain similar signal levels. Ratioing the signal and multiplying by the calibration data for the calibrated lamp provides the average irradiance for the pulsed lamp in mW m-2nm-1 at 0.5m. Figure 1 depicts irradiance of 6427 Flashlamp, and 75 W DC arc lamp.

Irradiance of 6427 Flashlamp, and 75 W DC arc lamp

Figure 1. Irradiance of 6427 Flashlamp, and 75 W DC arc lamp

Monitoring of the repetition frequency provides the total spectral energy density in mJ m-2 nm-1 at 0.5m because of the average pulse, by dividing the number of pulses per second. The validity of the measurement method relies on the fidelity of the integration by InstaSpec™. For all tests, Oriel Instruments uses special high speed chopper wheels to produce pulses of different duration from a continuous source. This verifies that InstaSpec™ indeed generates valid calibration data.

Calculating Source Output

Oriel Instruments provides two types of Pulsed Sources, namely, Series Q Based Pulsed Sources and "Integrated" Pulsed Sources. The Series Q systems employ the well-known Series Q Housing, and their output is estimated just as a CW source is, by finding the irradiance value from the spectral irradiance curves and multiplying the irradiance value in the bandwidth of interest by the factor summarized in Table 1. The "Integrated" systems employ a reflector based housing like the 7340 and 7341 Monochromator Illuminators. For these systems, the reflector multiplication factors listed in Table 5 are used.

Table 5. Conversion Factors for “Integrated” Pulsed Sources

Reflector F/# Reflector Coating Magnification Conversion Factor
2 AIMgF2 1.26 0.054
4 AIMgF2 2.0 0.044

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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