Lighting is a crucial part of any grow, whether you rely on sunlight or entirely on grow lights. Radiation is critical for photosynthesis, and without it, plants will simply shrivel and die.

However, the impact lighting has on different climate conditions is often overlooked. The number of lights, type of technology, intensity, and spectrum has an effect on the plants’ behavior, as well as temperature and humidity.

How Grow Lights Affect Temperature

All lights emit heat, regardless of the type of light you use. Even the most efficient LED bulbs still radiate some heat.

It’s true, however, that modern LEDs are more efficient and emit substantially less heat than older incandescent lights or even the more efficient CFL lights that are still in use in many grow ops. But, in a closed growing facility with a lot of powerful grow lights, the heat provided by lighting is significant and can’t be ignored.

So, if you design your environmental controls without adjusting for full lighting, you’ll likely find yourself battling high temperatures, even in colder climates.

How Grow Lights Affect Humidity

Though many may not realize when it comes to grow rooms and greenhouses, lighting has a major impact on humidity. It affects humidity in two ways – through heat and through radiation.

As mentioned above, grow lights emit heat and increase the temperature. This rise in temperature affects the plants’ behavior, causing them to increase their transpiration. Of course, higher transpiration rates mean more water vapor in the air and higher absolute humidity in the space.

But it’s not just the temperature that increases humidity. The radiation itself also increases the plants’ transpiration, even without the heat.

Radiation is necessary for photosynthesis. So in the presence of radiation, plants open their stomata in order to absorb it. However, when the stomata are open, water also evaporates, leaving the plant in the form of vapor.

Higher radiation intensity will cause the plant to evaporate significantly more water. In a closed space, this, too, can make a major impact on humidity levels.

The impact light has on plant transpiration is substantial and is still being studied. In recent years, for example, it’s been shown that the blue side of the light spectrum has a greater impact on stomata, increasing transpiration more than other lights. This is important, as many LED lights tend to lean more towards this side of the spectrum.

Combining Dehumidification with Grow Lights to Optimize Plant Growth

Understanding how and why lights affect humidity and temperature is crucial when designing a grow room or greenhouse. Without a complete picture of the environment you’re creating, it’s nearly impossible to optimize environmental control and provide the ideal growing conditions for your plants.

If the additional transpiration lighting creates isn’t taken into account, it won’t be possible to match sufficient dehumidification. Humidity will inevitably rise to 100%, risking mildews and other diseases. The same should be considered whenever changing or adjusting the lights in your facility.

Matching the right amount of dehumidification to your plants’ transpiration isn’t just crucial in preventing diseases. It also creates ideal growing conditions, stimulating the plants to grow faster and larger and produce higher-quality buds.

In fact, dehumidifiers and grow lights are a perfect combination. Additional lighting may enhance photosynthesis, but only if humidity levels allow it. If the relative humidity in the space is too high, the plants won’t benefit from the added lighting. This is an important point to remember whenever adding grow lights or increasing intensity.

Grow Room Example

Let’s use an example to simplify things. Say, under current lighting conditions, your plants evaporate water at a peak rate of 4 gallons per hour. In this case, a single dehumidifier, such as a DryGair DG-X, would provide adequate dehumidification by extracting up to 4.2 gallons per hour. This rate would keep relative humidity at the determined set point.

However, after adding additional grow lights in order to improve growth, the plants now transpire 5 gallons per hour. Now a single DG-X dehumidifier won’t be able to keep up, causing humidity to spike during peak hours.

In this case, not only do you risk mold development, but you also won’t get the benefits from the additional lighting.

A Well-Designed Grow Room Matches Dehumidification to Lighting

There’s no doubt that grow lights and dehumidifiers are both crucial in any grow room design.

However, in order to maximize the benefits of both, you should always match your dehumidification capacity to your plants’ maximum transpiration rate under full lighting.