Key points of this article:

• Standard horticultural LED lights lose between 10 and 15% of their light output per year, a phenomenon invisible to the naked eye but with measurable agronomic consequences.
• Two luminaires displaying the same initial PPFD can produce radically different results after 24 months, due to spectral drift related to the oxidation of components.
• Sulfur present in greenhouse environments perforates the silicon of diodes and corrodes the lead frame, causing an irreversible drift in the light spectrum.
• The guarantee of spectral stability over 5 years is the next normative criterion that will redefine horticultural tenders within 3 years.
• Dynamic sensor-based control solutions make it possible to actively compensate for this drift in real time, paving the way for high value-added predictive maintenance.

You invest in high-quality LED lighting, your energy bills remain stable, and yet your yields are gradually declining. Your technicians detect no faults. Your consumption data is unchanged. So why are your plants growing less well than they were 18 months ago? The answer lies neither in your substrate nor in your nutrient formulations. It lies in a criterion that virtually no tenders yet measure: spectral degradation over time.

This silent phenomenon affects all farms that have installed horticultural LEDs without requiring a guarantee of spectral stability over time. The lights continue to illuminate, the meters display reassuring values, but the spectrum delivered to the plants has insidiously changed. This physiological shift, imperceptible to the human eye, is nevertheless sufficient to cause abnormal elongation, increased susceptibility to disease, and a decline in crop quality.

This article presents the precise mechanisms of this degradation, its documented agronomic consequences, and the regulatory framework that will transform purchasing criteria in the professional horticultural sector by 2028. What you read here, your competitors will learn in their next calls for tenders.

Spectral degradation: why are your LEDs silently destroying your yields without triggering any alarms?

Spectral degradation refers to the gradual change in the wavelength-by-wavelength composition of the luminous flux emitted by an LED as it ages. It's not a complete failure: the light fixture still works, consumes energy, and emits light. However, this light is no longer quite the same as it was on the first day of use.

"Standard luminaires lose between 10 and 15% of their luminous efficacy per year under greenhouse operating conditions." - VGD summary based on ams-OSRAM Application Note data, 2024

This figure needs to be translated into operational reality. On a farm using 200 lights, this represents the equivalent of 20 to 30 lights becoming agronomically inefficient within a single annual cycle, without the monitoring system issuing any warning. The core problem is not the failure of the LEDs, but their chemical and thermal aging, which imperceptibly shifts the emission peaks of the spectrum while maintaining an apparently stable electrical power output.

Plants, however, perceive this shift. Their photoreceptors—phytochromes, cryptochromes, phototropins—are calibrated to precise wavelengths. A shift of just a few tens of nanometers in the deep red or blue is enough to alter the gene expression of plant growth, without your eye or your lux meter detecting the slightest anomaly.

The PPFD paradox: why can two lights displaying the same figures produce radically different agronomic results after 24 months?

PPFD – Photosynthetic Photon Flux Density – measures the number of photosynthetically active photons reaching a surface per second. It is the dominant criterion in all current calls for tenders. However, this figure reveals nothing about the spectral composition of these photons, nor about its stability over time.

Let's consider a documented case study. Two identical farms simultaneously install lighting fixtures with a photon flux density (PPFD) of 800 µmol/m²/s at startup. Twenty-four months later, both installations maintain a PPFD close to 750 µmol/m²/s. Their energy monitoring spreadsheets are virtually identical. However, one farm observes an 18% drop in the quality of its microgreens, while the other maintains its production standards. The difference does not stem from the total photon flux, but rather from the spectrum of these photons: one of the installations has undergone measurable spectral drift in the far-red (730 nm) and blue (450 nm) wavelengths, the two wavelengths most susceptible to the chemical aging of diodes.

Criterion	Initial PPFD (Day 0)	PPFD at 24 months	Spectral stability at 24 months	observed agronomic impact
Standard LED (market)	800 µmol/m²/s	~690 µmol/m²/s	Drift of 8 to 12% on deep red	Elongation, decreased quality, increased susceptibility to diseases
VGD rugged LED	800 µmol/m²/s	>760 µmol/m²/s	Mitigation < 10% over 5 years	Stable yields, spectrum maintained at target wavelengths

This table illustrates why PPFD alone is an insufficient indicator for assessing the true performance of a horticultural light fixture over its lifespan. The market is beginning to understand this. The most advanced specifications already incorporate it.

What is the number 1 molecular enemy of your LED diodes in the greenhouse?

In a greenhouse environment, sulfur is ubiquitous. It comes from pesticides, certain fertilizers, building materials, and fumigation. This gas, even in minute concentrations, poses a direct threat to the physical integrity of your LEDs.

"The silicone used in LED encapsulation is porous. In the presence of gaseous sulfur compounds, it allows corrosive molecules to pass through, reaching the lead frame, oxidizing it, and altering the internal reflection of the diode." - ams-OSRAM Application Note, 2024

This phenomenon of gas permeation through the silicone constitutes what electronic reliability engineers call contact corrosion . It is invisible, progressive, and irreversible. Once the lead frame is oxidized, the diode's ability to reflect photons back to the lens is permanently impaired: the spectrum shifts, the flux decreases, and no conventional maintenance operation can correct the situation.

The technical solution lies in what VGD calls molecular sealing: advanced chemical protection of components at the nanoscale, combined with thermal engineering that keeps the diode junction below critical temperature thresholds. After 25,000 hours of use at 85°C, components protected in this way retain more than 95% of their initial efficiency, according to reference data established by manufacturers of high-reliability components.

What are the concrete agronomic consequences of an uncorrected spectral drift?

The effects of spectral drift on plant physiology manifest gradually, often mistaken for substrate, nutrient, or pathogen problems. Identifying spectral degradation as the root cause requires a diagnostic approach that few farms have structured.

Here are the most frequently observed symptoms in farms affected by this phenomenon:

• Abnormal stem elongation (partial etiolation): A relative decrease in blue light (440-470 nm) in the delivered spectrum reduces the inhibition of elongation. The plants respond as if they were lacking direct light, by stretching their internodes.
• Decline in the quality of microgreens and young plants: Early growth stages are particularly sensitive to spectral variations. A 10% drift in the far-red (730 nm) range alters the Pr/Pfr ratio of phytochrome and disrupts germination and cotyledon development.
• Increased susceptibility to fungal diseases: Plants subjected to chronic light stress exhibit a weakened immune response. Their cell walls are less robust, and their secondary metabolism—particularly the production of defensive phenolic compounds—is less active. Pathogenic fungi find a favorable environment.
• Reduction in the content of active ingredients: In the production of aromatic or medicinal plants, the synthesis of essential oils and antioxidants is directly controlled by the UV and blue spectrum. Spectral drift measurably impacts the market value of the harvested product.

These symptoms share a common characteristic: they appear gradually, over several production cycles, and their spectral cause remains invisible without dedicated measurement instrumentation. A greenhouse manager who only monitors overall PPFD and electricity consumption has no way of detecting them in time.

What new performance standard should replace the initial PPFD as the evaluation criterion for horticultural lighting?

The relevant criterion for evaluating a horticultural luminaire in 2026 is no longer its photon flux at startup. It is its ability to maintain the spectral composition of this flux over time, under real operating conditions, for a contractually guaranteed period.

This paradigm shift is reflected in an indicator that VGD actively promotes: the guarantee of spectral stability over its service life . In practice, this means that a certified luminaire must demonstrate an attenuation of less than 10% of its initial photonic efficiency over 5 years of operation in a corrosive atmosphere.

"State-of-the-art engineering maintains attenuation of less than 10% over a 5-year period, even in the corrosive atmospheric conditions typical of commercial greenhouses." - Treegers Europe, Diode Lifecycle Expertise

To achieve this level of performance, three technical factors are non-negotiable:

1. The quality of the components: Only components meeting the most demanding reliability standards (AEC-Q102 certifications or equivalent) guarantee long-term performance in humid and corrosive gas conditions.
2. Thermal engineering: The junction temperature is the primary factor accelerating spectral aging. A properly sized heat sink keeps the diodes below the critical threshold, regardless of ambient conditions.
3. Chemical protection of components: The materials used in its construction and encapsulation must form an effective barrier against the permeation of sulfur gases. It is this molecular impermeability that differentiates a "ruggedized" LED from a standard LED.

How do predictive maintenance and dynamic sensor-based control actively compensate for spectral drift in real time?

Even the best diodes undergo natural aging. The most advanced approach is not just to delay this aging, but to continuously measure it and dynamically correct its effects before they impact crop physiology.

This is precisely the purpose of the intelligent light sensors integrated into VGD control solutions. These devices measure in real time the actual illuminance received by the crops—not the nominal electrical intensity of the luminaires, but the photon flux actually delivered to the leaves. When the sensor detects a deviation from the reference spectral profile recorded during commissioning, the control unit can automatically adjust the intensity of the affected modules to maintain the target DLI across the entire canopy.

This active compensation capability fundamentally transforms the economics of professional horticultural lighting:

• Luminaire replacement intervals are driven by real data rather than theoretical schedules.
• Production variability between different areas of the same greenhouse is reduced, even in the case of differential aging of the lighting fixtures.
• The operator has a documented history of lighting performance, which can be used during quality audits or contract renewals.

All of these features are 100% compatible with agro-climatic managers used in professional farms, allowing for seamless integration into existing control infrastructures.

What future horticultural tenders will require: what normative criteria will be imposed within 3 years?

The professional horticulture sector is moving towards a gradual standardization of performance requirements over a service life. Signs of this change are already visible in the most technical tenders and in industry reference publications.

By 2028, the specifications for the most demanding operations – intensive production greenhouses, plant research centers, phytopathology laboratories – will likely incorporate the following requirements:

• 5-year spectral stability certificate: supplied by the manufacturer with documented measurement protocol and reference environmental conditions (temperature, humidity, concentration of sulfur compounds).
• Resistance to corrosive atmospheres: chemical protection class certified by an independent laboratory, beyond the simple IP ratings for mechanical and water protection.
• Compatibility with spectral monitoring systems: standardized communication protocols enabling integration into existing agro-climatic managers.
• Aging data under real-world conditions: historical field data rather than simple projections from accelerated laboratory tests.

Suppliers unable to document these guarantees by 2027-2028 will be structurally disadvantaged in the most competitive tenders on the market. Operators who anticipate these criteria in their purchasing plans now will secure their productivity AND be in a stronger negotiating position for future equipment renewals.

To illustrate the issue concretely, here is the script of a conversation that our technical teams structured around this topic - in 45 seconds, the problem and the solution:

0-15 seconds: "Your lamps are 2 years old, your bill is the same, but your yields are dropping. Why?"

15-30 seconds: "It's not your plant, it's spectral drift: your diodes are oxidizing because of the air in your greenhouse."

30-45 seconds: "VGD installs molecular protection on its LEDs. We don't sell lamps, we guarantee your productivity for the next 5 years."

F.A.Q

What is spectral drift and how is it measured in a horticultural operation?

Spectral drift refers to the gradual change in the wavelength-by-wavelength composition of the luminous flux emitted by an LED as it ages. It is measured with a calibrated spectroradiometer, positioned at canopy level, by comparing the current spectrum to the reference spectrum recorded when the luminaire was commissioned. A deviation exceeding 5% in the target wavelengths (red 660 nm, blue 450 nm) should trigger a thorough evaluation of the installation.

Can the sulfur present in my greenhouse actually damage my LED lights?

Yes. Sulfur gas, even in minute concentrations (a few ppb), permeates through the silicone encapsulating diodes. It reaches the metallic lead frame, oxidizes it, and irreversibly alters the diode's internal reflectivity. This phenomenon is documented by ams-OSRAM in a 2024 technical note. The only effective protection relies on an advanced chemical barrier applied to the components during manufacturing.

What is the difference between a standard LED and a "hardened" LED in terms of spectral longevity?

A standard LED loses between 10 and 15% of its luminous efficacy per year under greenhouse conditions. A ruggedized LED, designed with high-reliability components, optimized thermal engineering, and advanced chemical protection, maintains an attenuation of less than 10% over 5 years of operation. After 25,000 hours of use, these high-quality, protected components retain more than 95% of their initial efficiency, according to component manufacturers' reference data.

How do smart light sensors help compensate for spectral drift?

Light sensors installed in the fields measure the actual photon flux received by the plants in real time. When a deviation from the reference profile is detected, the control unit automatically adjusts the intensity of the relevant modules to maintain the target DLI (Daily Light Intensity). This active compensation helps maintain agronomic performance despite the natural aging of the diodes and provides precise documentation of performance history for quality audits.

What additional budget should be allocated for luminaires with a 5-year spectral stability guarantee?

The additional cost of purchasing a ruggedized LED luminaire with molecular protection and guaranteed spectral stability varies depending on the power and configuration. However, the economic calculation must include the cost savings over five years: early replacement of degraded luminaires, yield losses due to uncompensated spectral drift, and the impact on the market value of crops. In most professional setups, the return on investment is positive from the third year of operation.

Conclusion: Anticipate the next standard so you don't have to be affected by it

Spectral degradation is no longer a concept reserved for photonics engineers. In the next 36 months, it will become the central criterion for purchasing decisions in professional horticultural lighting. Operators and technical managers who have structured their evaluation criteria around spectral stability over the lifespan of the equipment will be in a position of strength, while those who continue to purchase solely based on the initial PPFD (Phase Degradation Factor) will face unexplained yield losses and premature equipment replacements.

The horticultural industry is moving towards precision lighting agriculture: each wavelength is quantified, managed, and guaranteed over time. Dynamic sensor-based control solutions, coupled with ruggedized luminaires resistant to the corrosive atmospheres of greenhouses, represent the technological path that will become the benchmark in the most demanding tenders.

Vegetal Grow Development, based in Eyragues, Provence, supports horticultural operators and plant research teams who want to anticipate these changes rather than react to them. If you wish to assess the spectral stability of your current installations, or integrate this criterion into your next equipment project, contact our technical teams for a personalized audit. 💡🌱