Temperature
High temperatures cause increased respiration, sometimes above the rate of photosynthesis which means that the products of photosynthesis are being used more rapidly than they are being produced.

High temperatures cause added nutrients to injure the leaves, reducing their ability to assimilate light.
Low temperatures can be equally detrimental as they slow photosynthesis resulting in lower yields.

For growth to occur properly, photosynthesis must be greater than respiration.

Thermoperiod
Thermo-Period refers to the change in temperature between day and night.

Plants will produce maximum growth when daytime temperature are approximately 80F (+/- 2F) and night time temperatures are approximately 15F (+/- 5F) lower.

This allows the plant to photosynthesize during the optimum daytime temperature then limits the rate of respiration during the cooler nighttime