The Effect of Light Intensity on a Chemical Reaction

John Foxx/Stockbyte/Getty Images

Light intensity can seriously affect the speed of a chemical reaction. The amount of light directly influences the temperatures surrounding the reaction which can cause the speed of the chemical reaction to speed up or slow down in proportion to the affect of light on the temperature.

Light intensity is a catalyst with regard to chemical reactions and can drastically alter the outcome of the reaction as an additional influence on the chemicals being used.


The temperature at which a chemical reaction takes place often affects the intensity and speed of the reaction itself. A reaction that takes place in a higher temperature setting may speed up or work at a higher intensity level than a reaction that takes place in a colder temperature. Some cold temperatures can even slow down the reaction drastically or stop it altogether. Often in a laboratory situation temperature is a controlled element of the experiment. Light intensity can greatly affect the temperature, depending on the type of light and the proximity of the light source to the chemical reaction.

Natural Light

The intensity of natural light with regard to a chemical reaction may affect the reaction in a different way than if the chemical reaction was not taking place near a natural light source. The main source of natural light is sunlight which greatly affects temperatures outside. UV rays do not adversely effect the reaction, just the heat created by the intensity of the light, except in the case of chemical reactions that involve plant life.

Artificial Light

Exposure to artificial light sources creates a less dramatic effect on chemical reactions than exposure to natural light. Artificial light, such as fluorescent light which is common in classrooms and laboratories where chemical reaction experiments are conducted, has little to no effect on chemical reactions. Most artificial lights have little effect on the temperature of the room around them when used in moderation. Lights that are on for a prolonged period of time or that use high-wattage bulbs increase the temperature in the room, causing a change in the chemical reaction taking place. The chemical reaction is also affected by artificial light intensity from a close source, such as a lamp placed directly over the chemical reaction.

Instrument Lights

During some chemical reaction experiments, instruments are used to measure, observe, or record the chemical reaction as it happens. Some of these instruments are equipped with lights which allow the observer to see better while using the instrument. Though these lights can be helpful to observers, they can also affect the chemical reaction taking place. The lights, while small in wattage, are high in intensity because of their close proximity to the reaction. The light intensity from these instruments can increase the heat at the chemical reaction site, directly affecting the reaction. To avoid this, use instruments without lights or ones with lights that can be turned off.