Most effecting wavelength of light for photosynthesis is

The most effective wavelength of light for photosynthesis is Red.
The non-absorbed part of the light spectrum is what gives photosynthetic organisms their colour and is the least effective for photosynthesis in the respective organisms.
In green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light.
Photosynthesis measurement systems are not designed to directly measure the amount of light absorbed by the leaf. But analysis of chlorophyll-fluorescence, P700- and P515-absorbance and gas exchange.