How to Make Photometric & Colorimetric Measurements of Light Sources using an Ocean Optics Spectrometer and SpectraSuite Software

Transcription

1 How to Make Photometric & Colorimetric Measurements of Light Sources using an Ocean Optics Spectrometer and SpectraSuite Software This is a concise guide to setting up and calibrating your Ocean Optics spectrometer for making measurements of the illuminance and colour of a light source. Ocean Optics SpectraSuite software is a very powerful and versatile application, but light source measurements only require that you use a small proportion of its capabilities. The aim of this guide is to acquaint the operator with only that information necessary to perform light source measurements. For a more complete review of SpectraSuite, please refer to the operator manual that comes as a PDF file on the software installation CD. In terms of hardware, you will have an Ocean Optics spectrometer (e.g. USB2000+) with optical fibre and cosine diffuser (CC-3). You will also need a calibrated reference light source (e.g. LS-1-CAL). This guide assumes that you have previously installed SpectraSuite on your computer and copied the calibration files for the reference light source onto the computer (e.g. save them on the Desktop). A. Hardware Preparations 1. Connect the spectrometer to a USB port on your PC using the supplied USB cable. 2. Launch the SpectraSuite software application. 3. Remove the dust cap from the input to the spectrometer and attach one end of the optical fibre. 4. Attach the CC-3 cosine diffuser to the other end of the optical fibre. 5. Insert the CC-3 into the opening on the end of your reference light source. On the LS-1-CAL, you may first need to remove the SMA connector using the Allen key supplied (the SMA connector is left in place if the CC-3 diffuser is not fitted to the fibre, but we strongly recommend that you do not use a bare fibre for photometric or colorimetric measurements). 6. Insert the power jack into the rear of the calibrated light source and turn it on. (N.B. we recommend that you keep a log book to record how long you operate the calibrated light source for each time you use it. The calibration of the LS-1-CAL is valid for 50 hours of operation). Pro-Lite Technology LLP, 2009 Page 1 of 20

2 B. Performing a New Calibration The first time that you use the spectrometer (and at regular intervals thereafter), you need to create a new absolute irradiance calibration as follows. Please note that when you launch SpectraSuite, a spectrum graph opens automatically. This is called Graph (A). Ocean Optics refer to this chart as displaying spectral data in Scope Mode. Be very careful not to use Scope Mode data; scope mode is useful only for gauging the level of light relative to the spectrometer s dynamic range. Scope Mode simply charts the spectral power distribution in units of counts (Y axis) versus wavelength (x-axis). It is important to understand that the spectrum displayed in Scope Mode neither allows you to infer quantitative nor qualitative information about a light source. In other words, the shape of the spectrum will be displayed incorrectly in scope mode. This is because the raw data does not take account of the spectral sensitivity of the spectrometer and sampling optics. Even if you don t need to determine absolute light levels, and simply wish to see the spectral shape of a light source, you must perform a calibration against a reference light source. This is called a Relative Irradiance calibration, but this guide will explain how to perform an Absolute Irradiance calibration. An absolute irradiance calibration not only reports the absolute value of the light (spectral irradiance is reported in μw/cm2.nm), it also correctly displays the spectral power distribution (the spectral shape). Pro-Lite Technology LLP, 2009 Page 2 of 20

3 1. Select File, New, New Absolute Irradiance Measurement to open the Absolute Irradiance Calibration Wizard. 2. Select New Spectral Acquisition, then click on Next. Pro-Lite Technology LLP, 2009 Page 3 of 20

4 3. The spectral source (i.e. spectrometer) that you wish to calibrate will be highlighted as shown below. Click on Next. 4. Select New Calibration then click on Next. Pro-Lite Technology LLP, 2009 Page 4 of 20

5 5. Click on the Set Automatically button to set the optimum integration time. The software will choose a measurement integration time that corresponds to about 85% of full scale. For the USB2000+, the full scale is about 65,000 counts, so the optimum integration time will be when the Last Peak Value is about 55,000 counts. 6. Click on the Advanced Settings button and click in the check box next to Electric Dark Correction. 7. Set Scans to Average to 3, then click on Next. 8. Store the Reference Spectrum by clicking on the yellow light bulb icon then press Next. Remember to switch your reference light source off at this stage to help maintain the calibration life of your lamp. Pro-Lite Technology LLP, 2009 Page 5 of 20

6 9. Store a Dark Spectrum. First you must block off all light going into the spectrometer. The best way of doing this is to remove the fibre from the input to the spectrometer and replace the dust cap. Once you have blocked the light, click on the black light bulb and press Next. Pro-Lite Technology LLP, 2009 Page 6 of 20

7 10. Load the calibration data file for your reference lamp into SpectraSuite. To do this, click on Browse and navigate to the location that you saved the calibration files to (e.g. the Desktop). Select the file with the _CC suffix in the file name this is the correct file for the case of the CC-3 cosine diffuser fitted to the input of the optical fibre. An example of the file name is LSC2105_CC.LMP. Now press Next. 11. Select Fibre Diameter and enter the value 3900 (this is the diameter of the CC-3 diffuser). Pro-Lite Technology LLP, 2009 Page 7 of 20

8 12. Click on the Save to File button to save your new calibration. The default file location chosen by SpectraSuite is C:/Program Files/Ocean Optics/SpectraSuite/spectrasuite/bin. Use a naming convention that helps you to remember what the calibration relates to, for example you could use the file name CC-3 Irradiance Cal 23 Sept 09.IrradCal. 13. When you press Finish, the calibration wizard closes and a new chart will appear in SpectraSuite called Absolute Irradiance (B). Note that the other chart Graph (A) continues to display the raw counts versus wavelength data from the spectrometer. This is termed scope mode. Please note that in scope mode, the shape of the spectrum for any light source will be displayed erroneously scope mode should not be used for anything other than judging whether the light level is sufficient. Pro-Lite Technology LLP, 2009 Page 8 of 20

9 C. Performing a Photometric Measurement Once you have created and saved an absolute irradiance calibration, you can now start to make photometric measurements on one of your own light sources. With the spectrometer equipped with an optical fibre with cosine diffuser at its input, you are able to measure the illuminance (in lux) from a light source. Remember that illuminance varies with the distance between the receiver and the light source, so be sure to record your working distance when measuring illuminance. Point the optical fibre towards your light source and hold it in place. 1. Click on the I icon in the tool bar at the top right of the main SpectraSuite tool bar to perform a new absolute irradiance measurement. This is a similar process to the calibration that you have just performed, but now you will load the calibration you just created rather than creating a new calibration. 2. Select New Spectral Acquisition, then click on Next. Pro-Lite Technology LLP, 2009 Page 9 of 20

10 3. The spectral source (i.e. spectrometer) that you wish to use for the measurement will be highlighted as shown below. Click on Next. 4. Select the calibration that you just created from the list of saved calibrations. Press Next. Pro-Lite Technology LLP, 2009 Page 10 of 20

11 5. Select Fibre Diameter. The collection diameter of 3900 should already be showing. Press Next. 6. Click on the Set Automatically button to set the optimum integration time for your test light source. The software will choose a measurement integration time that corresponds to about 85% of full scale. For the USB2000+, the full scale is about 65,000 counts, so the optimum integration time will be when the Last Peak Value is about 55,000 counts. Please note that the USB2000+ has a minimum integration time of 1ms; if the light level is too high (i.e. above 55,000 counts) at 1ms, you will need to move the fibre further away from the light source. Press Next. Pro-Lite Technology LLP, 2009 Page 11 of 20

12 7. Click on the Advanced Settings button and click in the check box next to Electric Dark Correction. 8. Set Scans to Average to 3, then click on Next. 9. Store a Dark Spectrum. First you must block off all light going into the spectrometer. The best way of doing this is to remove the fibre from the input to the spectrometer and replace the dust cap. Once you have blocked the light, click on the black light bulb and press Finish. Pro-Lite Technology LLP, 2009 Page 12 of 20

13 10. Select Show Data in New Graph and then press Accept. 11. Click in the new chart area to activate the controls. Click on the candle icon at the far right in the tool bar directly above the chart area. Pro-Lite Technology LLP, 2009 Page 13 of 20

14 12. Click the Accept button when the Configure Photometry dialogue box opens. 13. The Photometry Report window will appear as shown below. Note that we have not defined the steradian field of view of the spectrometer so the values displayed for candelas will be erroneous. Similarly, you are not using an integrating sphere so the value for lumens will also be wrong. The illuminance (lux) value on the other hand is correct! Note the use of engineering format in the reported values E2 means 2 x 10 2 which equals 200, while E3 equals 2 x 10 3 or 2,000. Pro-Lite Technology LLP, 2009 Page 14 of 20

15 D. Performing a Colour Measurement Once you have created and saved an absolute irradiance calibration, you can also start to make colour measurements on your own light sources. The colour parameters which SpectraSuite computes include CIE chromaticity xy (2º observer), u v (10º observer), CCT (correlated colour temperature), dominant wavelength and colour rendering. Point the optical fibre towards your light source and hold it in place. 1. Click on the chromaticity diagram symbol (multicoloured triangle) in the tool bar at the top right of the main SpectraSuite tool bar. 2. In the New Colour Measurement dialogue box, select New Absolute Irradiance Processing and press Accept. Pro-Lite Technology LLP, 2009 Page 15 of 20

16 3. The spectral source (i.e. spectrometer) that you wish to use for the measurement will be highlighted as shown below. Click on Next. 4. Select Get Irradiance Calibration from file and click on Next. Pro-Lite Technology LLP, 2009 Page 16 of 20

17 5. Select the calibration that you just created from the list of saved calibrations. Press Next. 6. Select Fibre Diameter. The collection diameter of 3900 should already be showing. Press Next. Pro-Lite Technology LLP, 2009 Page 17 of 20

18 7. Click on the Set Automatically button to set the optimum integration time for your test light source. The software will choose a measurement integration time that corresponds to about 85% of full scale. For the USB2000+, the full scale is about 65,000 counts, so the optimum integration time will be when the Last Peak Value is about 55,000 counts. Please note that the USB2000+ has a minimum integration time of 1ms; if the light level is too high (i.e. above 55,000 counts) at 1ms, you will need to move the fibre further away from the light source. 8. Click on the Advanced Settings button and click in the check box next to Electric Dark Correction. 9. Set Scans to Average to 3, then click on Next. Pro-Lite Technology LLP, 2009 Page 18 of 20

19 10. Store a Dark Spectrum. First you must block off all light going into the spectrometer. The best way of doing this is to remove the fibre from the input to the spectrometer and replace the dust cap. Once you have blocked the light, click on the black light bulb and press Finish. 11. Select the Emissive Mode (this is always the selection when measuring light sources). Also select reference illuminant E for normalisation (this affects the calculation of dominant wavelength) then press Accept. Pro-Lite Technology LLP, 2009 Page 19 of 20

20 12. The Colour Report window and CIE Degree Observer Chromaticity Diagram will appear as shown below. Prepared by: Robert Yeo Pro-Lite Technology 24 h October 2009 Pro-Lite Technology LLP, 2009 Page 20 of 20