Images are too dark compared to those on the monitor

Since the images on the monitor are illuminated from behind and this is not the case with your photo product, there is a slight difference in brightness despite having a calibrated monitor. For this reason, we offer an ICC profile that serves to simulate the paper and darkens the image a little so that it can be brightened accordingly.

We recommend the following monitor settings:
Brightness: 90 - 120 candela/sqm
Colour temperature: 5,000 Kelvin (D50)
Gamma value: 2.2

Tone correction check: 

As an additional check, we recommend checking the tonal value correction of your images. With the tonal value correction, you can determine whether tonal values are present in all areas of your image. If you notice that there are no tonal values in the lights (or also in the depths), this indicates an incorrect monitor calibration (monitor is set too bright or too dark). If there are no more lights in your file, we recommend a revision of the image file until the first tonal values are visible in the lights.

Images are too dark compared to those on the monitor

If the tonal values are correctly distributed, it may be that your monitor is too bright.

Another reason for dark images could be an incorrect or absent color profile.
All information about the color profiles you can use can be found in the Professional Zone.

Lights are missing: 

Images are too dark compared to those on the monitor

Lights are missing, image is generally too dark:

Here, only in the middle to low tones tonal values ​​are obtained, the picture will appear very dark and low in contrast

Images are too dark compared to those on the monitor

 

Depths are missing: 

The picture lacks the contrast and the depths will look dull. 

Images are too dark compared to those on the monitorheImages are too dark compared to those on the monitor

The tonal values ​​are well distributed in the image and present in every area, there will be no problems: 

 

Images are too dark compared to those on the monitor

 

If the tonal values ​​are distributed correctly, your monitor may be too bright. 

Another reason for too dark images could be a wrong or no embedded color profile. 
All information about the color profiles you can use can be found  here