Which reactions in photosynthesis require light?
To put it simply, there are two reactions in photosynthesis, the light dependent reaction and the light independent reaction. And as the name implies, the light dependent reaction requires light.
The light dependent reaction of photosynthesis requires energy in the form of light so as to convert CO2 and H2O into glucose and other substrates. The light independent reaction does not require light but can also occur in the presence of light.