Measuring bright lights

Researchers at the National Institute of Standards and Technology (NIST) have developed two new calibration tools to help check the accuracy and correct the performance of instruments that use fluorescence to identify substances.

NIST has created two fluorescent glass Standard Reference Materials (SRMs), the size of a packet of chewing gum, using certified values.

Using fluorescence spectroscopy, scientists can detect, measure and identify unknown substances, including chemical and biological weapons, by sending a beam of light at a certain wavelength into a sample. The beam then excites electrons in particular fluorescent labels, known as analytes, which then emit light at longer wavelengths with energy levels that can be measured.

A fluorescence spectrometer is used to measure this light, known as the spectral signature, and each is unique depending on the fluorescent compounds.

The SRM 2940, known as the Orange emission, was made to measure emission wavelengths from 500 to 800 nanometers when excited with light at 412nm. The SRM 2941, known as the Green emission is able to measure emission wavelengths from 450 to 650nm when excited with light at 427nm.

For instance, to use the SRM 2941 to calibrate a fluorescence spectrometer, researchers would excite the glass with a light at 427nm and collect the emission from 450nm to 650nm. The measured intensity values could then be compared with the certified values to determine the accuracy of the testing instrument.

NIST claims that the certified SRMs are resistant to decomposition caused by light (photodegradation), and that they can also be used with non-tunable wavelength selectors, such as filter-based fluorometers and microscopes.