This webpage/application is meant as an interactive, educational tool for amateur astronomers and others alike. It allows picking a light source from a list, like the Sun or sections of the solar spectrum (perhaps pre-filtered), and then to apply two tunable filters, to check the effects of double stacking for example: more about suppressing the wings than the fwhm.
 
An image is synthetized on the right, a very rough approximation as the Sun there is through a single etalon, hence no chance of showing a double stacked view, and a spectroheliogram is out of question.
 
For observing the Sun, mainly in narrow-ish bands, I really needed to bring myself up to speed about light. Here's an article I wrote recently Altair Astro’s 3nm CaK Ultra filter: testing, comparison, review.
 
This tool's professional shortcomings, like finding the perhaps imperfect balance between speed and rounding errors are something I hereby apologize for. Adding two functions together on a whiteboard is one thing, adding thousands of interpolated datapoints and rendering images based on them is another, theory vs practice.

On the one hand there is the marketing side of amateur astronomy filters, reduced to advertising the FWHM along with mentioning the CWL as a name.
 
Hydrogen Alpha 2.8nm Super Hyper Giga Ultra Max Narrow Band. Cavity count, peak transmission, wings, optical density? Nothing.
 
On the other hand, finding scientific data in search engines that are designed not to serve results but to hog our attention is a PITA. So here are some useful links, beyond what I already showed: