This has not been changed. It is likely that you were using using a different luminance model in your older files.
If you want the illumination to "scale" with the geometry, it is necessary to select a luminance model that considers the physical area of the light. Both Lumens (lum/m^2) and Luminance (cd/m^2) are defined in terms of area, so lights with this model will appear the same regardless of the Scale Model setting. On the other hand, the Power + Efficacy, Lumens, and Candella models define the total output of the object, so lights with this specification will appear brighter when the scene is scaled down.
You can also change your camera exposure, if necessary.