When the Long Exposure NR is set to ON on your Nikon camera, the camera will work to reduce the image noise for you. But that comes with a caveat; you will have to wait about the same time as your exposure time, for the camera to do it’s job. That’s in fact doubling the time between shots. I’m not gong to comment on the use of LE-NR. But if you ever use it, make sure that you understand the implications. I had an interesting experience, when I was taking some fireworks pictures. LE-NR was set to ON on my D90 and guess what, I missed some nice fireworks display, while the camera was working for me. So be careful when you use this nice feature. Folks, “you learn from my mistakes”.