LensFlare, a Universal app, is currently free. It lets you add a variety of lights and textures to an image.
Noir Photo, also a Universal app, allows you to convert a daylight photo to a nighttime photo. It’s currently $2.99.
The image above was created in about a minute. Positioning lights with LensFlare is a bit annoying, since you can’t zoom in on the image when trying to place the light. Also, if you rotate your iPhone/iPad 90 degrees, the location of the flare will shift. That is where most of the time goes, and of course deciding on a “look” for the shot in Noir Photo. I went with basic grayscale.