Illuminance is the term used for the light flux (in lm), which impinges on a surface, based on the size of the area. Derived (Si) unit is the Lux (lx). She is a photometric unit. If a luminous flux of one lumen evenly illuminates an area of one square meter, the illuminance on the illuminated surface is 1 lux (1lx = 1lm/m2). A candle at a distance of one meter produces an illuminance of about one lux.
If you double the distance between the candle and lighted surface, the illuminance falls to 0.25 lux, because the illuminated area is growing with the distance squared. Illumination can be intensityfied by focussing the emitted light flux, by reflectors or lenses for example, to a smaller area.
The illuminance, if no information for distance to illuminated surface or illuminated area is given, cannot be used to compare light sources.