Dear Muhammad, do you want to measure or to calculate the illuminance? For measurements, you would take an illuminancemeter... To calculate, you may rely on a dedicated lighting simulation software. Otherwise you may implement something like the lumen method, if you want in matlab.
If you are trying to calculate the illuminance you could also use the photometric distribution of the light you are using (one format is called an *.IES file) and a tool like Photometric Tool ( https://www.visual-3d.com/tools/photometricviewer) to estimate the illuminance on a surface.