Choosing A Light Source For Your Spectrometer

Most spectroscopy experiments require at least one light source. Electroluminescence measurements use an external current as an excitation source. However, most characterization of an optical material requires some sort of incident light. 

• Photoluminescence and fluorescence measurements require a high-energy monochromatic light sources, often in the UV range.
• Monochromatic light sources can be useful for absorbance spectroscopy when measuring optical density. These measurements are often standardized to a specific wavelength. 
• Absorbance measurements require illumination over a broad wavelength range, so require a broadband light source such as the Ossila LED Light Source.
• A tunable light source provides an adaptable combination of monochromatic and broadband light sources. These light sources can cycle through a range of wavelengths to build a broadband spectrum, or can be used to isolate individual wavelengths of light.  

There are multiple other factors to consider when choosing light sources for an spectroscopy lab. Choosing the best light source depends on:

• Type of measurement or experiment
• Specifications of your spectrometer or spectrophotometer 
• Compatibility with other spectroscopy components (i.e. rail based systems, optical fiber compatibility, etc)
• Budget
• Safety restrictions
• Available set-up and maintenance time 

You will likely need different light sources for different optical measurements. Therefore, it is quite likely that you will need more than one light source in order to fully characterize your organic electronic materials.

 

Comparing Different Spectroscopy Light Sources

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In the table below, we have done a brief comparison of different light sources. Here, we have outlined their ideal applications, costs and other important information.

 

	White Light LEDs	Tungsten Halogen + Deuterium Light Sources	Monochromatic LEDs	Lasers	Tunable Light Source
Type	Broadband	Broadband	Monochromatic	Monochromatic	Monochromatic
Suitable measurements	Absorbance measurements Transmission measurements Reflectivity measurements	Absorbance measurements Transmission measurements Reflectivity measurements	Photoluminescence Optical Density Measuring concentration of certain molecule	Photoluminescence / Steady State Fluorescence ASE Time-resolved spectroscopy (for pulsed laser systems)	Absorbance Photoluminescence Fluorescence Transmission Excitation / Emission Spectra
Advantages	Long bulb lifetimes	Wide spectral range	Long bulb lifetimes	High power (for weak fluorescence), can emit short pulses for TRPL	High versatility
Cost	Low	High	Low	Mid-range to High	Mid-range to High
Emission Spectra	Broad spectrum  (360 nm – 900 nm for Ossila LED Light Source)	Very broad spectrum (190 nm – 2200 nm)	Well-defined narrowband emission (e.g. 370 nm for Ossila USB UV Light Source - 700 nm for the Ossila USB Infrared Light Source)	Well-defined emissions (can be tunable depending on the laser)	Narrow emission but over a wide wavelength range (Ossila Tunable LED Light Source can select a wavelength 380-1000 nm with < 1 nm accuracy)
Warm-Up Time	Minimal	30 minutes – 1 hour	Minimal	5–60 minutes (will vary depending on laser material and mode)	Minimal
Temperature Control Needed?	Not needed for small LEDs, larger LEDs often have integrated cooling fans	Yes – to stop overheating	Not needed for small LEDs, larger LEDs often have integrated cooling fans	Most likely – but depends on the laser	Not needed for small LEDs, larger LEDs often have integrated cooling fans
Set Up and Calibration Time	Low	Low	Low	High	Low
Safety Considerations	Low	Low	Low–Medium	High	Low

In order to take the broadest range of general spectroscopy measurements, you will need multiple light sources, such as can be found in our LED Light Source Set or the Tunable LED Light Source.

Ossila Light Sources

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Ossila sell many low-cost light sources which are compatible with the Ossila USB Spectrometer, but also with other spectroscopy equipment via the use of standard optical fibers. This will enable you to take a range of spectroscopy measurements quickly and easily.

In combination, these two light sources will provide you with everything you need to take basic spectroscopy measurements. These are compatible with standard spectroscopy fittings (SMA 905 fiber connections, M6 optical breadboard holes) so that they can be easily integrated with any spectroscopy system.

LED Light Sources Set

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