How Lighting Layout Affects DLI

Ever wondered why some of your plants flourish while others seem to struggle, even though they’re all under the same lights? The answer may lie in your lighting layout, which affects the Daily Light Integral (DLI). Factors like the height, spacing, and arrangement of your fixtures all contribute to the light field in your grow space. This, in turn, determines how much usable photosynthetic light actually reaches your plants throughout the day.

If you want every plant in your grow space to receive the right amount of light and thrive with lush, healthy growth, it’s time to take a closer look at your lighting setup and ensure your plants get the best possible conditions for growth.

What is DLI and why it matters

Daily Light Integral refers to the total amount of photosynthetically active radiation (PAR) that plants receive over a 24-hour period. It represents the cumulative light energy available for photosynthesis each day and is measured in mol/m2/day. DLI combines both the intensity and duration of light.

As light is a primary energy source for plants, DLI directly impacts how quickly plants grow and how much they yield. For flowering and fruiting plants, specific DLI levels are required to trigger and sustain their reproductive stages. Understanding DLI is key to ensuring that plants receive the right amount of light, especially for controlled environments like greenhouses and indoor farms.

However, the amount of natural sunlight plants receive can vary significantly due to factors like latitude, time of year, and time of day. These fluctuations make it difficult to estimate how much light plants are actually getting on a daily basis. That’s where DLI map becomes important. With Daily Light Integral Map, you can determine the amount of sunlight a specific region receives at different times of the year. With this data, you can calculate how much supplemental light is needed to achieve the optimal lighting for your crops.

How lighting layout affects DLI

The layout and arrangement of grow lights play a crucial role in determining how light is distributed throughout the growing space. This directly impacts the DLI.

First, let’s take a look at how DLI is calculated. In an indoor farm where plants receive 100% artificial light, the DLI can be calculated using the formula:

DLI = PPFD x Lighting Hours x 3600/1,000,000

From this, we can see that PPFD is the primary factor affecting DLI when the lighting hours are constant.

PPFD (Photosynthetic Photon Flux Density) is the number of photons in the PAR range hitting one square meter of plant surface per second (measured in μmol/m²/s). Lighting layout affects the PPFD, or the light intensity, and thus affects DLI. Here’s why:

Fixture height

Raising the fixtures increases the coverage area but reduces PPFD intensity. As the distance between the light source and the plant increases, the light intensity decreases, spreading over a larger area.

Lowering the fixtures increases PPFD because the light is concentrated over a smaller area, but it also creates a more intense light gradient. This can lead to uneven light distribution, potentially causing some areas to receive too much light while others get too little.

Fixture spacing

The spacing between fixtures is another critical factor in achieving optimal light distribution. If the fixtures are spaced too far apart, it can result in "dead zones" where light intensity is too low for healthy plant growth. On the other hand, placing fixtures too close together can cause energy waste and create hotspots where the light intensity is too high.

Optimizing lighting layout for uniform DLI

To achieve uniform DLI for your plants, it’s essential to optimize the lighting layout. Here are some practical strategies to help you optimize lighting layout:

A light plan

A light plan is a vital tool that accurately stimulates the amount and layout of artificial lights needed for your growing environment. It helps you visualize how much light each crop will receive, ensuring you meet the specific light needs of your plants. This plan can also help determine how to distribute light most effectively to support plant growth at all stages. A well-designed plan considers both the natural light available and the supplemental lighting required to achieve the target DLI.

At Atop, we offer free light plants tailored to your specific needs. Reach out to us for assistance in optimizing your lighting setup.

Install grow lights at two levels

A single-level lighting setup may not deliver a uniform DLI across your growing area. Plants have different light needs at various growth stages, and placing lights at two levels can help distribute light more evenly. For example, groHERE places fixtures installed at two levels for their strawberry plants strawberries to provide the same DLI to plants.

Use inter-canopy light

While top lighting is common in horticulture, it may not always provide adequate light to the lower parts of taller or vining plants. In these cases, the light may not penetrate deep enough to support healthy growth in the lower canopy. To address this issue, consider using inter-canopy lighting, which supplements the light at mid or lower levels of the plant canopy.