On a higher tier exam, you may be asked to explain why moving a light source closer to a plant increases the rate of photosynthesis. The less the distance, the greater the light intensity. The reverse is also true. The greater the distance, the lower the light intensity. The relationship between distance and light intensity can be represented like this.
Light intensity is inversely proportional to the distance squared. The inverse square law means that if you halve the distance, the light intensity will be four time greater.
We can use all this data and knowledge to maximise productivity of plants for commercial growth. We use green houses to artificially manipulate plants by increasing certain limiting factors. Often greenhouses will feed carbon dioxide into plants and maintain a higher temperature compared to the outside in order to increase the rate of growth.
Carbon dioxide levels are increased by using paraffin heaters which release carbon dioxide as a by-product. Some greenhouses provide artificial lights to increase photosynthesis by giving the plants more light to use. Farmers and horticulturalists monitor levels carefully as this will allow them to maximise profits by providing the plants with the resources they need, but not in too great a quantity as this would cost money for no added productivity.