Lightroom is automatically darkening my photos

suddie1215 wrote:

What camera brand and model are you using?  Check the menus to see if you have features like Auto Lighting Optimizer and Highlight Tone Priority (Canon) or Active D-Lighting (Nikon) turned on in your camera.

The reason for the change you're noticingis that Lightroom and Adobe Camera Raw (they share the same processing engine) do not read all the in-camera settings for Raw files.The only  in-camera settings read by Lightroom/ACR are White Balance, ISO, aperture and shutter speed.   All other settings such as Picture Styles/Controls, in-camera sharpening, saturation, contrast,  etc. are not read and applied.
When your import first Raw files into Lightroom you initially see preview thumbnails based on the JPEG file embedded in every Raw file. Then as the software caches the images, the JPEG-based preview is removed and replaced with one that only uses the settings listed above.  And if you use settings like ALO, HTP, or Active D-Lighting that artificially lighten shadows areas in your photos, the change is even more dramatic and your photos will look dark in Lightroom.  But its all the first step, you can easily adjust the sliders to make the photos look exactly as you want.