Lumen is a measurement of light output, but who knows how they measure it. The first shot was at a shutter speed of 1/6 second and the second at 1/13 which would indicate that the second was twice as bright.

Here is your second shot with adjustment to the WB, exposure and contrast. These are all things that can be adjusted in the camera if you do not want to mess with post processing. I cannot get your background perfectly white.

Novice lighting help-dsc_0041.jpg

I assume that you are shooting in jpg file format. Are you using the maximum Quality and Size? (Not sure of the Nikon terms, but the best.)

TF