Switching to LED Grow Lights? Watch Your Humidity

Switching to LED grow lights is a smart move for growers. These lights offer numerous benefits, from energy efficiency to better spectral control. However, there's one important factor to consider: LED grow lights can affect humidity in unexpected ways.

Unlike HPS lamps, LEDs produce less radiant heat. This means less evaporation, which can lead to higher humidity levels in your grow space. As a result, your usual watering and climate control methods may not work as effectively as before.

But don’t worry, we’ve got you covered. In this blog, we’ll explain how LEDs impact humidity and share tips to help you maintain the perfect environment for your plants.

Why LED Lights Increase Moisture in Grow Rooms

After switching from HPS to LED grow lights, many growers notice that moisture levels in their grow rooms are higher. This issue has been particularly evident for Dutch tomato growers, who have experienced increased humidity in their greenhouses when using LEDs. Crop consultant Willem Valstar points out that, while LED lights are energy-efficient, they often require additional heating and dehumidification to control moisture levels and maintain optimal growing conditions, especially during the winter months.

So, why does this happen?

HPS lights are relatively inefficient, converting only about 30% of their electrical input into visible light. The remaining 70% turns into heat. On the other hand, LED lights are much more efficient, converting 40-50% of their power into usable light for plant photosynthesis (PAR). While LEDs do produce some heat, it’s far less than HPS lamps. This reduction in heat can lead to lower evaporation, resulting in higher humidity in the grow space.

The Importance of Humidity in Plant Growth

Humidity plays a crucial role in plant health and growth for several reasons.

Transpiration and Nutrient Delivery

The most important factor is how humidity affects transpiration and nutrient transport. Plants lose water through tiny pores in their leaves, called stomata. This water loss creates a "pull" that draws water and nutrients up from the roots to the leaves. When humidity is low, the air is dry, causing water to evaporate too quickly. As a result, plants struggle to replenish the lost moisture, leading to wilting, stress, and poor nutrient uptake. On the other hand, high humidity can hinder transpiration, making it harder for nutrients to travel within the plant and potentially contributing to problems like root rot.

Cell Turgor and Plant Structure

Humidity also impacts cell turgor, which is the internal pressure of plant cells against the cell wall. This water pressure is essential for maintaining cell structure, supporting plant shape, and enabling growth. Low humidity can cause dehydration and wilting, while high humidity can make cells waterlogged and weak, leading to structural issues.

Plant Disease Development

Humidity also plays a key role in the development of plant diseases, especially those caused by fungi and bacteria. High humidity creates an environment conducive to the growth of mold and mildew, while low humidity can attract pests, such as spider mites, that thrive in drier conditions.

Common Problems After Switching to LEDs

Switching to LED grow lights brings many benefits, but it also introduces humidity-related challenges that can significantly impact plant health and overall climate control.

One of the most immediate issues is increased condensation on plant leaves, especially during early morning hours. Because LED fixtures emit less heat than traditional lighting, moisture accumulates more easily, leading to water droplets on fruits and flowers, which can increase the risk of disease.

This occurs because LED lighting affects vapor pressure deficit (VPD)—the difference between the air’s moisture-holding capacity and its actual moisture content. Higher humidity levels result in lower VPD, which slows plant transpiration. This, in turn, can lead to slower nutrient uptake, irregular flowering patterns, and reduced pollination success.

For growers, managing the climate becomes more complex. Dehumidification systems may struggle to keep up with increased moisture levels. Heating systems need to run longer to compensate for the reduced warmth from LEDs. Air circulation also requires adjustments to maintain optimal conditions. All of these factors lead to increased maintenance, higher energy costs, and even additional investment in climate control equipment.

Effective Humidity Management After Switching to LED Grow Lights

Transitioning to LED grow lights significantly changes the environment inside a grow space, making effective humidity management crucial. Since LEDs produce less heat than traditional lighting, you must take a multi-faceted approach to maintain optimal conditions.

Monitor and Record Environmental Changes

The first step is to track humidity and temperature changes after switching to LEDs. Using a reliable hygrometer and thermometer, regularly monitor these levels and keep detailed records. This helps identify trends and potential issues early, allowing for proactive adjustments.

Adjust Watering Practices

With LEDs, there is less heat-driven evaporation, meaning plants may require less water than before. Overwatering in this lower-evaporation environment can lead to root rot and other moisture-related issues. Monitoring soil moisture and adjusting irrigation accordingly is essential to maintaining healthy plant growth.

Upgrade Dehumidification Systems

The shift to LEDs alters moisture dynamics, often requiring dehumidification system updates. Since LEDs reduce overall heat load, you must recalculate your dehumidification needs and possibly add supplemental units in key areas. The goal is to create an independent humidity control strategy that doesn’t rely solely on temperature fluctuations.

Compensate for Reduced Heat with Supplemental Heating

Since LEDs don't produce as much radiant heat, additional heat may be required to maintain consistent temperatures. This could mean using horizontal airflow heaters to ensure uniform temperature distribution, implementing under-bench heating to keep the plant roots warm, or adjusting your greenhouse heating system to maintain minimum pipe temperatures. The goal is to replace the lost radiant heat while ensuring an even temperature across the entire grow area.