I got a Mars Hydro grow light as recommended by mjlorton for indoor PV testing, and it works great, just one problem: I get a huge AC component on top of the DC voltage coming out of the solar panel, sometimes as large as 50%. This is not good for recording power data and also not what the actual sun does. This problem was easily solved by adding a large capacitor in parallel to the solar panel output (At least 1000 mikroFarad).