Which light range is most effective in photosynthesis?

Hint: The process in which plants prepare their food in presence of their sunlight is known as photosynthesis.

Complete answer:
The most effective light range in photosynthesis is :-
i) Red range ($600$to $700$nm) and blue range ($425$ to $450$nm) furthermore, red light is more effective in photosynthesis because both the photosystem ($PS1$ and $PS2$) absorb light of wavelength in the red region $680$nm & $700$nm respectively.
ii) Blue light is absorbed by carotenoids, which pass the energy to the chlorophyll. Since the maximum absorption by chlorophyll occurs in red light. It is the most effective wavelength for photosynthesis. Chlorophyll strongly absorbs red light. Thus it is effective at photosynthesis.
iii) Red light is a longer wavelength lower energy light while blue light is higher energy. That makes it impossible to assign a single wavelength of best absorption for all plants. All plants, however, has chlorophyll a, which absorb most strongly at ~$450$nm, or a bright blue colour. Blue light carries a higher energy signature than a red light does and the higher energy with a shorter wavelength should provide the plants with a better environment for growth.
iv) Red and blue ranges are not used by most plants, & can contribute the heat buildup in plant tissues.
v) Many plants grown under only red light, such as plants grown indoors under only red LED’S
Have a stretched, elongated appearance, the leaves are thin and large and plants become tall. In most cases, plants grown under only red light do not have desirable growth characteristic. However, when a relatively small amount of blue light is added to red light, the extension growth of the plant is inhibited. Therefore, plants are grown indoor with $80$ to $90$ percent red light & $10$ to $20$ percent blue light are quite compact, with smaller leaves and shorten stems. In greenhouses, plant receives a wide solar spectrum and so the colour of light provided by supplemental lighting has much less impact on extension growth.

The best wavelengths of visible light for photosynthesis fall within the blue range (425–450 nm) and red range (600–700 nm). Therefore, the best light sources for photosynthesis should ideally emit light in the blue and red ranges.

Note: Whereas in green light the photosynthesis is least because the plants do not absorb this range of light reflect back thus, they appear green. If the plant are expose to green wavelength, the rate at which the photosynthesis take place will be least. This is due to the presence of green pigment known as chlorophyll.