49. Energy balance and cost/lux/PAR ratios

Why energy balance is the real bottleneck of indoor farming

In an advanced indoor hydroponic system, electricity is the main operating cost item. In particular, lighting accounts for between 50 percent and 70 percent of total consumption on average, making it the most critical factor in the economic sustainability of the system.

Evaluating an LED system only by installed watts or declared lumens is an incomplete and often misleading approach. The correct question is not how much energy is consumed, but how much of that energy is actually converted into useful plant growth.

To answer this we need correct metrics and a systemic analysis that relates:

• energy cost (euros)
• quality and quantity of light emitted
• biological response of the plant

Lux: a misleading metric for indoor growing

Lux measures the illuminance perceived by the human eye, weighted by visual sensitivity. Plants, however, do not respond to light in the same way.

Two light sources with the same lux value can have:

• completely different spectra
• opposite photosynthetic yields
• radically different impacts on growth and morphology

An LED designed for the human environment may be energy inefficient in an agricultural setting while appearing very "bright."

👉 Key conclusion: lux is not a reliable metric for evaluating the efficiency of a hydroponic system.

PAR and PPFD: the light that plants actually use

PAR (Photosynthetically Active Radiation) covers the spectrum between 400 and 700 nm, which is the radiation actually used by photosynthesis.

The operating parameter is PPFD (µmol/m²/s), which indicates how many PAR photons strike a surface every second.
PPFD is directly related to:

• growth rate
• plant structure
• final yield
• energy consumption per cycle

In other words, PPFD measures the functional quality of light, not its visual perception.

From technical to economic data: euro/ PAR

In a professional plant, the key metric is not the watt, but the real cost of photosynthetically useful light.

The correct reasoning is:

How many euros do I spend to provide the plant with the amount of PAR it needs to complete the cycle in the shortest possible time?

This leads to an implicit operational indicator:

• euros per µmol PAR actually used

Two systems with the same electrical consumption can generate:

• longer or shorter cycles
• very different yields
• costs per kg produced that are not comparable

Fixed spectrum vs. dynamic spectrum: where energy is wasted

Fixed-spectrum LEDs, although powerful, tend to:

• over-illuminate non-critical phases
• generate light stress
• produce unnecessary heat
• accelerate chip degradation

In advanced systems, however, light becomes a dynamic variable, modulated according to the actual phenological stage of the plant.

This makes it possible to:

• reduce PPFD when it is not needed
• increase it only at key times
• improve the ratio of grams produced/kWh

LED Tomato+: light efficiency as a controlled variable

In the case of Tomato+ LEDs, the energy balance is addressed upstream in hardware and software design. LED arrays with 6 independent spectral channels, controlled by proprietary firmware, allow only useful PAR to be delivered at each stage of the cycle, avoiding waste typical of fixed-spectrum LEDs.

The intensity and spectral composition are not static, but dynamically modulated by the Growth Plan, which adapts PPFD and photoperiod to the actual phenological stage of the plant.

Added to this is an often overlooked but decisive element: liquid cooling.
Active thermal management makes it possible to:

• keep PPFD stable over time
• reduce LED degradation due to thermal stress
• avoid spectral drift over long cycles
• increase the lifetime of the arrays

The result is a system in which light output does not degrade with hours of use, and energy efficiency remains constant cycle after cycle. In Tomato+ systems, luminous efficiency is not a nameplate specification, but a biological and economic variable optimized in real time.

The real energy balance: beyond LEDs

A professional assessment must include the entire system:

• lighting and spectrum
• cooling and dissipation
• pumps and recirculation
• layout and clearances
• degradation of components over time

Only a comprehensive analysis can tell whether a plant is:

• truly efficient
• scalable
• economically sustainable

Conclusion: the metrics that separate hobbyists and professionals

In advanced indoor farming:

• lux is a secondary metric
• watts are only a starting point
• the decisive metric is how much useful PAR you get per euro spent, over time

Those who ignore this approach waste energy and reduce margins.
Those who master it build more stable, more productive and truly scalable systems.

Thank you for reading this article. Keep following us to discover new content on hydroponics, vertical farming, and smart agriculture.

Tomato+ Team