How emerging biophotonic research is changing what we know about underwater light absorption
Light behaves differently underwater than it does in air, and that difference has profound consequences for every system designed to function in a marine environment. For offshore fish farmers, understanding how light travels, transforms, and interacts with living organisms beneath the surface is no longer purely academic. A growing body of biophotonic research is redefining the assumptions that have guided aquaculture lighting design for decades, and the practical implications are significant.
This article builds from foundational science to real-world application. It begins by defining biophotonics and its connection to marine environments, then examines the physical mechanisms that govern underwater light absorption, before exploring what recent research reveals about how marine organisms actually perceive light. From there, it translates those scientific insights into principles for aquaculture lighting design, identifies where conventional assumptions break down in offshore conditions, and closes with a framework for building a science-informed lighting strategy for offshore fish farms.
What is biophotonics and how does it relate to underwater environments?
Biophotonics is the scientific discipline that studies the interaction between light and biological systems. It draws on optics, biology, and physics to understand how living organisms emit, absorb, scatter, and respond to photons across the full electromagnetic spectrum. The field encompasses everything from how photoreceptors in the eye detect colour to how light-sensitive proteins regulate biological rhythms at the cellular level.
In underwater environments, biophotonics takes on particular complexity because the medium itself, seawater, is not optically neutral. Unlike air, water actively filters, scatters, and transforms light as it travels downward. This means the light that reaches a fish, a photoreceptor, or a marking lantern at depth is fundamentally different from the light that entered the water at the surface. Biophotonic research is now mapping these transformations with precision, revealing how marine organisms have evolved to function within a radically altered light environment.
For those working in offshore aquaculture, this matters because lighting systems are designed in air and deployed in water. The assumptions built into a lantern’s optics, colour output, and intensity ratings are based on above-surface performance. Biophotonic research provides the scientific basis for understanding what actually happens to that light once it enters the marine environment, and how the organisms in that environment respond to it.
How water absorbs, scatters, and transforms light
Water does not transmit all wavelengths of light equally. As sunlight or an artificial light source enters seawater, specific wavelengths are absorbed at different rates depending on the physical and chemical properties of the water column. This selective absorption is the first and most important mechanism that separates underwater optics from surface optics.
Absorption by wavelength
Red wavelengths, which sit at the longer end of the visible spectrum, are absorbed most rapidly. In clear oceanic water, red light effectively disappears within the first few metres of depth. Orange and yellow wavelengths follow a similar pattern, attenuating quickly as depth increases. Blue and green wavelengths, by contrast, penetrate far deeper, which is why the deep ocean appears blue to the human eye. In coastal and nearshore waters, dissolved organic matter and suspended sediments shift this balance further, often absorbing blue light and allowing green wavelengths to dominate.
Scattering and diffusion
Beyond absorption, water also scatters light. Scattering occurs when photons interact with particles suspended in the water column, including phytoplankton, sediment, and organic detritus. Scattering does not destroy light energy the way absorption does, but it redirects photons, diffusing the beam and reducing the directional coherence of a light source. A focused beam that travels cleanly through air becomes increasingly diffuse as it travels through seawater, with the rate of diffusion determined by turbidity. In offshore environments, turbidity can vary significantly with season, weather, and location, making the effective range of any underwater light source highly variable.
The combined effect
The combined result of absorption and scattering is described by a parameter called the attenuation coefficient, which quantifies how rapidly light intensity decreases with depth for a given wavelength in a given water body. Understanding attenuation is the starting point for any scientifically grounded approach to underwater light absorption and aquaculture lighting design.
What biophotonic research reveals about marine organism light perception
Building on the understanding of how water transforms light, biophotonic research examines the second half of the equation: how marine organisms detect and respond to the light that survives that transformation. The findings challenge several assumptions that have historically informed aquaculture lighting practice.
Fish photoreceptors, the specialised cells in the retina responsible for detecting light, are not uniformly distributed across the visible spectrum. Research into the opsin proteins that govern photoreception in fish has shown that different species have evolved peak sensitivity at wavelengths that correspond to the dominant light environment of their natural habitat. Deepwater species, for example, often show peak sensitivity in the blue range, precisely because blue wavelengths penetrate deepest in open ocean conditions. Nearshore and surface-dwelling species may show broader spectral sensitivity, reflecting the more varied light environment they inhabit.
Biophotonic research has also advanced understanding of non-visual photoreception in fish. Beyond the retinal system, fish possess extraretinal photoreceptors, light-sensitive cells located in the brain, pineal gland, and skin, that detect light independently of visual processing. These receptors govern circadian rhythms, reproductive cycles, and feeding behaviour. Crucially, they respond to specific wavelengths and intensities that may differ from those that trigger visual responses. A light source that appears effective from a visual standpoint may simultaneously disrupt biological timing mechanisms if it delivers the wrong spectral profile to these non-visual systems.
For aquaculture operators, the practical implication is significant: the biological effect of a light source on farmed fish cannot be predicted from its visible output alone. Spectral composition, intensity at depth, and the duration of light exposure all interact with both visual and non-visual photoreceptive systems in ways that affect fish health, growth rates, and behaviour.
Applying biophotonic principles to aquaculture lighting design
Translating biophotonic research into aquaculture lighting design requires moving beyond lumen output and visible range as the primary design criteria. The science points toward a more nuanced set of parameters that determine whether a lighting system achieves its intended biological and operational outcomes.
Spectral selection is the first principle. Because different wavelengths attenuate at different rates underwater, the spectral composition of a light source should be matched to the depth at which it needs to function and the biological response it is intended to produce. A light designed to support photoperiod manipulation in salmon, for example, must deliver sufficient intensity at the relevant wavelength at cage depth, not just at the surface. This requires working backwards from the target depth and the water’s attenuation characteristics to specify the surface output needed.
Intensity calibration at depth is the second principle. Surface intensity ratings provide no direct information about the light field experienced by fish at a given depth. Effective aquaculture lighting design requires modelling the attenuation of the chosen wavelengths through the specific water column in which the system will operate, accounting for seasonal variation in turbidity and dissolved organic content.
The third principle concerns temporal control. Biophotonic research has demonstrated that the timing and duration of light exposure is as biologically significant as its intensity and spectral composition. Light systems that can be programmed with precision, including graduated transitions that mimic natural dawn and dusk patterns, are more likely to support stable circadian rhythms in farmed fish than systems that switch abruptly between full intensity and darkness.
Systems designed for aquaculture lighting in offshore environments must address all three of these principles simultaneously, integrating spectral precision, depth-calibrated intensity, and programmable temporal control within housings that can withstand continuous exposure to saltwater, wave action, and biofouling.
Why conventional lighting assumptions fail in offshore conditions
Many aquaculture lighting systems have been designed using assumptions derived from either terrestrial horticultural lighting or from inshore, sheltered water applications. In offshore conditions, both sets of assumptions break down in ways that biophotonic research makes explicit.
The most common misconception is that a light source rated for a given intensity and range at the surface will deliver equivalent performance at depth. In offshore waters, where turbidity is driven by wave-induced sediment suspension, seasonal phytoplankton blooms, and oceanic mixing, the attenuation coefficient can shift dramatically over short periods. A system calibrated for summer conditions in clear water may deliver a fraction of its rated intensity at the same depth during a winter bloom event, precisely when reliable light delivery may be most critical for photoperiod management.
A second failure point is the assumption that visible output is the only relevant metric. As biophotonic research has established, non-visual photoreception in fish responds to specific wavelengths that may not be prominent in the output of a general-purpose LED source. A white LED array, for example, may appear bright and effective to the human eye while delivering minimal energy in the blue-green range that drives melatonin suppression in salmonids. Designing for human perception rather than fish photobiology produces systems that look adequate but underperform biologically.
Offshore conditions also introduce structural challenges that affect light delivery over time. Biofouling, the accumulation of marine organisms on submerged surfaces, degrades the optical performance of underwater light sources at a rate far exceeding what inshore operators typically encounter. Conventional maintenance schedules developed for sheltered environments are often inadequate for offshore installations, where access is limited and fouling rates are higher. The result is a progressive deterioration in light delivery that is rarely accounted for in initial system specifications.
Building a science-informed lighting strategy for offshore fish farms
A science-informed lighting strategy for offshore fish farms integrates the biophotonic principles established above into a structured decision framework. Rather than selecting lighting equipment based on surface-level specifications, operators should approach the design process in stages that mirror the scientific understanding developed throughout this article.
The starting point is site characterisation. Before specifying any lighting equipment, operators should establish the optical properties of the water column at the farm location across different seasons. This means measuring or modelling the attenuation coefficients for the relevant wavelength ranges at the depths where light delivery is required. Without this baseline, all subsequent design decisions rest on assumptions that may not hold in practice.
The second stage is biological specification. Working from the target biological outcomes, whether photoperiod manipulation, feeding stimulation, or predator deterrence, operators should identify the specific wavelengths, intensities at depth, and temporal patterns that the science indicates are effective for the species being farmed. This specification should be developed with reference to current biophotonic research rather than general horticultural or aquaculture lighting guidelines, which may not reflect the latest findings on fish photoreception.
The third stage is equipment selection and configuration. Lighting systems should be evaluated against the biological specification and the site’s attenuation characteristics, not against surface-level performance ratings alone. Key selection criteria include:
- Spectral output matched to the target wavelength range for the species and application
- Sufficient surface intensity to deliver the required irradiance at depth after accounting for site-specific attenuation
- Programmable temporal control with graduated transitions and GNSS synchronisation for consistent timing
- Housing and optical materials rated for long-term submersion, biofouling resistance, and offshore sea states
- Remote monitoring capability to detect performance degradation before it affects biological outcomes
The fourth stage is ongoing performance verification. Because attenuation conditions change seasonally and fouling degrades optical performance over time, a science-informed strategy treats lighting as a dynamic system requiring periodic review rather than a fixed installation. Remote monitoring systems that provide real-time operational data enable maintenance interventions to be timed based on actual performance rather than fixed schedules, reducing both operational cost and the risk of undetected underperformance.
Biophotonic research is still an evolving field, and the understanding of marine organism light perception continues to develop. Operators who build their lighting strategy on scientific principles rather than inherited assumptions will be better positioned to incorporate new findings as they emerge, and to demonstrate to regulators and certification bodies that their systems are designed with biological and operational rigour. The science is advancing; the lighting strategy should advance with it.
Contact Sabik’s technical team to discuss aquaculture lighting requirements for your offshore installation.
