Interview with Prashant Prabhat, Ph.D.

Feb 6, 2015 by IDEX Health & Science

The recent introduction of Semrock's LED Filter Sets has generated significant interest from the fluorescent microscopy marketplace. We asked Prashant Prabhat, Applications Scientist, to give us some insights into what the new filter sets mean and why they are providing such significant performance improvements.

IDEX Health & Science: What prompted Semrock to develop filter sets specifically for LED light sources?

Prashant Prabhat: We're always sensitive to how well our products serve our customers and have been closely watching developments in LED technology and their adaptation in fluorescence microscopy.  With the advances in solid-state light source technology, we realized that the new spectral signatures of the LED sources demanded response from filter manufacturers. Semrock is a market leader in developing innovative products that provide optimized solutions. To serve the fluorescence imaging community, we've been providing filter sets for different types of light sources including broadband light sources such as Xenon and metal halide lamps.  However, these conventional filter sets may not provide optimal imaging performance with LED sources. So we were among the first to recognize the need to adapt to take advantage of the new LED technology.

IDEX Health & Science: Can you share some background insights  on current challenges in LED light engine (LE) optimized filter solutions?

Prashant Prabhat: Popular LED LE manufacturers provide very capable light sources.  When operating as stand-alone units, the brightness of these LEs is fairly impressive. However, high brightness of the light sources rarely translates into the brightest fluorescence signal. This is where having an optimized filter solution makes a significant difference.

We found that few people outside the filter industry really understand the challenges that LEDs present in terms of providing a “buttoned-up” solution for imaging. To this effect, most of the LED LE manufacturers rightfully design as well as offer their LED LE products to accommodate optimal filtering solutions. This allows customers to use optimally designed filter sets with their LEs. However, in rare cases when a customer may attempt to mix-and-match filters from different sources, optimal performance is rarely achieved. When this happens, it's not uncommon to have customers contacting us with concerns about excitation light leakage, poor contrast, or significant loss of fluorescence signal. Semrock’s LED “filter sets” address these needs by providing a buttoned-up solution.

IDEX Health & Science: Can you discuss your approach to designing these new LED sets?

Prashant Prabhat: First of all, with LEDs, the whole spectral signature of the excitation source changes.  This is no surprise, but it means that existing solutions that worked well for bulb sources had to be thought through once again. In many cases, earlier solutions weren't able to take advantage of some of the improved spectral quality and ranges available from LEDs. A fresh look was needed.

We took a holistic approach in a multidimensional optimization of factors like brightness, contrast, signal-noise ratio, and other performance issues that make the significant difference between a merely functional imaging system and an optimized one.

IDEX Health & Science: Isn't it enough to find matching dichroic and emitter components for an off-the-shelf excitation filter in the LE?

Prashant Prabhat: There's much more to the problem. As a general principle, we do not recommend mixing and matching filters from different sources. This approach can significantly compromise imaging performance when compared to a buttoned up solution such a “filter set”. In the attached white paper, we've outlined some of the issues and concerns that our LED filter sets address for our customers.  We've stressed the multi-dimensionality of the problem, discussing factors many people don't consider --- like crossover-edge specifications of the excitation-emission filter pair, matching the proper wavelength ranges, and other problems that the filter sets solve.

IDEX Health & Science: How can someone investigate the new LED filter sets to learn what's best for an application?

Prashant Prabhat: Fortunately, Semrock has researched market needs and then developed LED filter sets that address these needs for the majority of our customers using LED LEs. For those who want to further investigate the compatibility of our filter sets for popular LED source / fluorophore combinations, we recommend using our Searchlight tool. This online resource allows plotting and visualization of fluorophore spectra, overlaid with the spectra of filter sets as well as LED LEs. Additionally, the Searchlight utility allows quantitative analysis of signal and SNR for various spectral combinations to make educated decisions about trade-offs among various alternatives.  Overall, the customer can get a fairly comprehensive view of how well a system will operate in a given configuration before making the equipment and filter investment.

We invite you to check out the SearchLight^™ tool and see for yourself how the LED filter sets are designed, or download our latest white paper.