How high should a horticultural LED lamp be placed?

Your basil is growing, the lettuce is almost touching the lamp, and you no longer know whether to raise the light. Conversely, seedlings that are stretching sometimes give the impression that the light is too far away. The right distance is not a universal figure: it depends on the power of the lamp, its spread, and the plant being grown.

Here is how to set the height of your horticultural lighting in an indoor garden, observe the leaves' reactions, and correct the situation without making random adjustments.

What distance should be left between the LED lamp and the plants?

The first indication to follow is that of your lighting manufacturer. A small LED bar designed to be close to young shoots does not work like a powerful horticultural panel intended to illuminate a large area.

Always measure the distance between the light surface and the top of the leaves, not between the lamp and the reservoir. As the plants grow, this space decreases, even if you have not touched any settings.

A distance in centimeters found on the internet cannot therefore apply to all devices. If your hydroponic garden has an adjustable mast, start with the setting recommended in its manual, then observe the growth for several days. If the lamp is not adjustable, favor compact varieties adapted to its height.

Why does the height of the lamp change growth?

Light generally becomes less intense as the source is moved away from the plant. But the intensity actually received also depends on the lenses, the shape of the panel, its angle, and the natural light entering the room.

Too little light can cause some young plants to stretch to find it. Conversely, too intense a light can cause discoloration or leaf stress. A lamp placed very close can also cause a heat problem depending on the device.

The goal is therefore not to systematically bring the panel as close as possible. It is to provide enough light, evenly enough, without putting the leaves in difficulty.

How to recognize a lamp placed too high?

When a young shoot receives too little light, its stem can become long and thin. Plants sometimes lean towards the light source and appear fragile. On already established plants, growth can also become sluggish.

These signs do not always come from the height. The daily lighting duration, the type of lamp, the temperature, and the general condition of the plants also play a role.

If you notice this phenomenon, first check that the lighting actually turns on at the scheduled times. If its height is adjustable, gradually bring it closer while respecting the manufacturer's limits. Then wait to observe the new leaves: they are more revealing of the improvement in conditions than the old already stretched stems.

To distinguish a distance problem from a duration problem, also consult our guide on the number of hours of light for a hydroponic garden.

How to know if the LED lamp is too close?

Pale or bleached leaves on the side of the lighting, dry or browned edges, and unusually compact development can signal excessive intensity. If the highest leaves are the most affected, the height of the lamp deserves particular examination.

Warning: a brown leaf does not prove on its own that an LED burned it. A problem with water, hydroponic nutrients, temperature, or roots can produce similar symptoms.

Start by observing which leaves are affected and where. If the damage is concentrated directly under the light panel, check the temperature around the foliage and raise the lamp slightly when the manual allows it. Do not let the leaves touch a lighting surface that is not designed for contact.

The already damaged parts will not always regain their initial appearance. Above all, monitor the quality of the new shoots after the correction.

How to adjust the lighting as growth progresses?

The easiest thing is to adopt a small routine rather than moving the lamp every morning.

1. At sowing: install the germination sponge and the growing basket according to the manual. Check the lighting programming intended for the species and the germination phase.
2. After sprouting: look to see if the young plants remain relatively stocky or start to stretch. Adjust only if necessary.
3. During growth: regularly check the space between the highest leaves and the lamp. Do not let a single large plant impose an unfavorable situation on the others.
4. Before harvest: remove the leaves ready to be consumed when the plant's harvesting method allows it, or rearrange the crops if they are shading each other.

One change at a time is enough: height, then observation. If you change the height, the lighting duration, and the nutrients simultaneously, it becomes difficult to know what is really helping.

Should the lamp be placed at the same height for basil and lettuce?

Not necessarily. Two species, or even two varieties of the same species, can develop foliage of different heights. If a basil dominates small lettuces, you risk raising the lamp to avoid contact with the basil while moving the lighting away from the lettuces.

In a small indoor garden, therefore, think about the adult height of the plants from the choice of seeds. Grouping compact crops of similar sizes greatly simplifies the adjustment. You can also harvest or prune certain plants when this operation suits them.

The amount of light needed also varies according to the use of the plant: growing leaves does not impose exactly the same requirements as supporting the flowering and fruiting of tomatoes or peppers.

To avoid these differences, we recommend choosing seeds adapted to the available space rather than systematically filling every growing spot.

What if the lamp is fixed or your installation has no built-in LED?

There are several indoor growing configurations. Some small systems have a built-in lamp with a height adjustment. Others use a separate lamp; others still depend mainly on the available natural light.

With a fixed lamp, especially adapt the selection of plants and their size. If you need to buy independent lighting, check the area to cover, the possibility of adjusting it, its electrical compatibility, and the distance instructions specific to the model.

A light window can contribute to the lighting, but its brightness varies greatly with the season, exposure, and weather. An installation without built-in horticultural lighting is therefore not equivalent to a system that has one.

When you compare the different formats of indoor gardens, consider lighting as a real choice criterion, on par with space and ease of maintenance.

Can the lamp be left on all day?

No, increasing the number of hours is not an automatic solution to lighting that is too far away. Plants also need periods of darkness, and needs vary according to the species and stage of development.

Respect the recommended programming for your equipment and your crop. A well-set duration will not always compensate for poor light distribution, and too high an intensity can remain problematic even during a short period.

A little check is better than a universal setting

To properly place a horticultural LED lamp, remember three reflexes: start with the manual, measure the distance from the top of the leaves, and observe the new shoots after each adjustment.

Stems that stretch can signal a lack of light. Pale leaves directly under the lamp can indicate excessive exposure. In both cases, also examine the water, the temperature, and the general condition of your hydroponic garden before drawing a conclusion.

Light accompanies growth; it does not dispense with filling the reservoir, adding the appropriate hydroponic nutrients, or maintaining your installation. With a few regular observations, the adjustment however becomes much more intuitive.