Light sources

We are developing lamps for UV, visible, and UV-vis spectroscopy.  Tungsten halogen lamps are commonly used to provide broad band visible light in spectroscopy applications.  The most common source of UV light for spectroscopic measurements is a deuterium lamp.

  In addition, we provide guidance below for building a lamp for calibrating your spectrometer based on the emission spectrum of commonly available compact fluorescent lights (CFL).

A fluorescent lamp for wavelength calibration

The easiest way to calibrate the wavelength axis for your spectrometer will be with light from a fluorescent lamp.  The spectra to the right (and seen all over this web site) is from a compact fluorescent lamp CFL.

 

  The light from a florescent lamp is emitted at discrete, known wavelengths.  The wavelengths of light from such a lamp are reported here.  The figure below the spectrum shows a home built CFL light source with a fiber optic connection.  The fiber connection is not necessary to calibrate your spectrometer but helps with keeping things aligned when something is moved about.

  Once you have light from the CFL, use the calibration user interface to determine calibration parameters and load them into the non-volatile memory of your spectrometer.  Once the calibration parameters are stored in to EEPROM, the values will be loaded into the normal user interface any time you use the instrument.  An embedded video demonstrating how the instrument is calibrated can be found on this page.

Tungsten Halogen Lamps for visible spectroscopy

​The visible lamps we choose are low voltage and low wattage.  For a visible spectrometer, 12 volt 10 watt bulbs seem appropriate.  These can be powered off a 1 amp "wall wart" DC power block.  I have read that low voltage bulbs will last longer than the 120 volt options and low wattage bulbs do not generate tons of heat.  If you build a mounting out of plastic or wood, you need to be aware of the heat generated by your lamp so you don't set stuff on fire.

The bulbs we get are two pin bulbs that use a G4 socket.  You can order these from us or find them at your local lighting store or on Amazon.  One thing I have noticed about using commercial lighting bulbs for spectroscopy is the presence of fairly sharp lines in the spectrum.  I suspect the lines are from halogen emissions.  I suspect that if you spend the big bucks at a spectroscopy store, you will get a bulb with less halogen and the lines will not be as pronounced.  The lines don't move, or change in intensity, so they do not worry me.

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Deuterium lamps for UV and UV-vis Spectroscopies

Spectroscopy in the ultraviolet is more expensive than in the visible.  Deuterium lamps have power requirements that are more stringent than visible lamps.  They require a high voltage to begin an arc discharge then a lower voltage to maintain the arc.  The lamp itself has to have quartz windows to be transparent to UV and an appreciable amount of deuterium in its atmosphere.

That being said, there is some question in my mind whether the prices charged for UV and UV vis lamps are appropriate.

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We have successfully built a UV-vis lamp using components largely purchased from vendors we found on Alibaba.com.  The only major issue with the lamp is heat dissipation, which would not be a problem if the housing we purchased (figures below) were made entirely of metal, rather than having plastic end plates. 

 

We had aluminum blocks milled to mount deuterium lamps we purchased.  The figure above right shows a block and bulb.  The forward face of the block has mounting holes for M5 machine screws and a through hole for the light path.  The light path hole passes all of the way through the block to allow mounting a tungsten halogen bulb behind the deuterium lamp (seen in the figure below left).  As shown in the figure below left, the UV-vis lamp requires two AC / DC converters, one for the deuterium lamp (inside the aluminum block) and the other for the tungsten halogen lamp (mounted inside a copper pipe, attached to the aluminum block).  In this configuration, light from the tungsten halogen bulb passes through the aluminum block and a hole in the electrodes of the deuterium lamp and exits co-incident with the UV.

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