One factor which affects transpiration rate is light. When it is lighter, the stomata is open, which allows carbon dioxide in for photosynthesis. This means that water can diffuse out the leaf, so there is a faster transpiration rate. Another factor is temperature. The higher the temperature, the faster the transpiration rate. Water can diffuse from the leaf due to evaporation, but also due to the difference in the water potential gradient. In addition, the lower the humidity, the faster the transpiration rate. This is because there is a higher water potential gradient, so more water diffuses out the leaf. Finally, the windier it is, the faster the transpiration rate. Again, water potential gradient is increased, so water diffuses out the leaf.