There is a way to have a good idea of how your solar cells will respond to a specific wavelength. Incident Photon to Converted Electron (IPCE) or External Quantum Efficiency (EQE) measurements will tell you how much current a solar cell will produce when illuminated with a specific wavelength. A quick search for silicon brings this example IPCE image for silicon, the figure at the bottom. Considering that the flashlight you link has a wavelength of 365 nm, it would seem that the cells would not generate a lot of current at that specific wavelength (but would do some).
To be honest, my recommendation would be to simply use a standard light bulb, maybe one with a bit higher wattage than the average - for solar simulators we use a very specific bulb but those are quite expensive! If you go to the bulb manufacturers themselves, (in our case Phillips) they will often show you the emission spectrum of the specific bulb you are looking at, which may help - but something with broad emission would do the trick. Alternatively if you wanted to use an LED and a specific wavelength, something in the 550-650 nm range would perhaps be better.