I’ve been struggling with lightroom issues of late, and this is to do with how Canon and Lightroom handle RAW files differently. Trawling the web others seem to have the same issue. RAW files look darker in Lightroom than they do in the image preview on the camera and how Canon’s DPP program renders them. After some research, I discovered that this is mainly due to the color profile Adobe uses for RAW files and the difference between that and what the camera uses. For RAW files, Lightroom uses the Prophoto RGB colourspace to render all files. Most cameras would probably be using sRGB colourspace. Because Prophoto is a wider colour gamut than sRGB the colour values are different and to have them in that range they appear darker. sRGB has a more compressed colourspace and hence the colours appear slightly brighter for the same colour values.