Help me to build some devices for measuring LEDs optical power[mW] with range (1 -100)mW included
Um that's really not the way a screen works.... 

A typical mobile phone screen is an OLED panel, with red green and blue oleds, you cannot control the wavelength other then by varying the power of each of these three diodes that actually radiate whatever spectrum they radiate. Certainly you cannot decide that you want energy at xxxnm and make the screen produce it.

In particular notice that there is NO WAY to make yellow light, but you can fool the human eye because human vision is (kind of, sort of) tristimulus rather then actually being particularly sensitive to wavelength as such.  

Surely you played with a prism in school? You might find one instructive, or possibly a diffraction grating? You will find that a mobile phone screen, looks a LOT like an RGB led in terms of spectrum.   

There is a graph on the second to last page of this paper that shows a fairly typical OLED emission spectra for the red, green and blue elements (Of an OLED telly, but phones are pretty similar). 

http://set.org.br/ijbe/ed2/06_IEEE%20format%20-%20Photometric%20and%20Colorimetric%20Comparison%20of%20OLED,%20NANOSP,%20and%20LCD.pdf