Fluorescent underwater photography represents an extraordinary dimension of marine exploration that transforms ordinary diving experiences into spectacular encounters with hidden underwater worlds. This revolutionary photographic technique reveals the mesmerizing phenomenon where marine organisms emit vibrant luminescence when exposed to specific wavelengths of blue illumination, creating otherworldly imagery that showcases nature's most enigmatic visual displays.
The sophisticated art form combines advanced scientific principles with creative photographic techniques, enabling underwater photographers to document previously invisible aspects of marine ecosystems. Professional photographer Lynn Miner has pioneered numerous techniques in this specialized field, demonstrating how fluorescent photography can reveal extraordinary details about marine life behavior, coral health assessment, and underwater ecosystem dynamics.
Through meticulous application of specialized lighting equipment, precision optical filters, and advanced camera configurations, fluorescent diving photography unveils breathtaking displays of natural bioluminescence that remain completely invisible under conventional white light illumination. This comprehensive exploration examines the intricate technical aspects, essential equipment requirements, and sophisticated photographic methodologies necessary for mastering this captivating underwater photography discipline.
Comprehensive Introduction to Marine Fluorescence Phenomena
Marine fluorescence diving encompasses the utilization of specialized blue wavelength illumination combined with precision barrier filtration systems to observe and photograph the remarkable bioluminescent properties exhibited by numerous underwater organisms. This extraordinary natural phenomenon occurs when marine creatures absorb high-energy, short-wavelength blue photons and subsequently emit lower-energy, longer-wavelength visible light through complex molecular processes.
The fundamental distinction between fluorescent emission and conventional reflected illumination represents a crucial concept for understanding this specialized photography technique. Traditional underwater photography relies entirely upon reflected light bouncing from subjects back toward the observer's eyes or camera sensor, whereas fluorescent photography captures actual light emission generated internally by living organisms through sophisticated biochemical processes.
Numerous marine species demonstrate remarkable fluorescent capabilities, including diverse coral species, soft tissue organisms, various fish species, sea anemones, and countless microscopic creatures. These organisms possess specialized proteins and cellular structures that facilitate the remarkable light conversion process, creating stunning visual displays that serve various biological functions including communication, camouflage, predator deterrence, and photosynthetic enhancement.
The revolutionary aspect of modern fluorescent diving techniques extends beyond traditional nighttime applications, encompassing sophisticated daytime photography methods that can reveal fluorescent phenomena under carefully controlled lighting conditions. Advanced practitioners have developed innovative approaches for capturing fluorescent imagery during daylight hours by utilizing strategic positioning, shadow manipulation, and high-intensity blue illumination systems.
Advanced Physics Principles Governing Fluorescent Light Emission
The electromagnetic spectrum encompasses an vast range of radiation wavelengths, with visible light occupying a relatively narrow band between approximately 400 nanometers representing deep violet coloration and 750 nanometers corresponding to dark red hues. Understanding these fundamental wavelength relationships proves essential for mastering fluorescent photography techniques and achieving optimal results in diverse underwater environments.
When high-energy, short-wavelength photons encounter specialized fluorescent proteins within marine organisms, these photons become absorbed by molecular structures, causing constituent electrons to undergo quantum mechanical transitions from their ground state energy levels to elevated electron shells. This quantum mechanical process represents a fundamental aspect of atomic physics where electrons can only occupy discrete energy levels with no intermediate positions possible.
The subsequent energy decay process occurs virtually instantaneously as excited electrons return to their ground state configurations, releasing photons with longer wavelengths and correspondingly lower energy levels than the original absorbed radiation. This wavelength shift phenomenon, scientifically termed the Stokes Shift in honor of Irish physicist George Stokes who documented this effect during the 1830s, forms the fundamental basis for all fluorescent photography applications.
Conservation of energy principles dictate that the emitted photon must possess lower energy than the absorbed photon, with the energy difference converted to thermal energy during the molecular transition process. This energy conversion explains why fluorescent emissions always exhibit longer wavelengths than the excitation radiation, creating the characteristic color shifts that make fluorescent photography so visually compelling.
The quantum mechanical nature of these transitions means that each energy level change represents discrete quantum jumps rather than gradual energy modifications. Greater energy level differences between electron shells result in more dramatic wavelength shifts, producing the spectacular color transformations observed in fluorescent marine photography where blue excitation light generates emissions spanning the entire visible spectrum.
Specialized Biology Underlying Marine Fluorescence Mechanisms
Green Fluorescent Protein, commonly abbreviated as GFP, represents the foundational biological molecule responsible for the majority of marine fluorescence phenomena observed in underwater photography applications. Originally discovered and isolated from Aequorea victoria jellyfish specimens during the 1960s, GFP has become one of the most extensively studied proteins in modern molecular biology research.
The remarkable discovery and subsequent development of GFP applications earned Osamu Shimomura, Martin Chalfie, and Roger Tsien the 2008 Nobel Prize in Chemistry, recognizing their groundbreaking contributions to understanding fluorescent protein mechanisms and developing practical applications for scientific research. Their pioneering work established the foundation for modern fluorescent imaging techniques used across numerous scientific disciplines.
The molecular structure of GFP contains a specialized region called the chromophore, which serves as the light-absorbing and light-emitting component of the protein molecule. This chromophore region possesses unique electronic properties that enable the absorption of blue wavelength photons and subsequent emission of green wavelength photons through the quantum mechanical processes described previously.
Various mutations and modifications of the original GFP molecule have produced fluorescent proteins capable of emitting different colors including yellow, cyan, red, and numerous other hues across the visible spectrum. These protein variants occur naturally in diverse marine species and can also be artificially created through genetic engineering techniques for research applications.
The evolutionary advantages conferred by fluorescent protein expression in marine organisms remain an active area of scientific investigation. Current research suggests multiple potential benefits including enhanced photosynthetic efficiency for symbiotic algae, improved camouflage capabilities against fluorescent coral backgrounds, intraspecies communication mechanisms, and protection against harmful ultraviolet radiation in shallow water environments.
Revolutionary Applications Beyond Aesthetic Photography
Contemporary marine fluorescence photography extends far beyond creating visually stunning imagery, encompassing crucial scientific applications that contribute significantly to marine biology research, conservation efforts, and environmental monitoring programs. Research institutions worldwide utilize fluorescent imaging techniques to investigate fundamental questions about marine ecosystem health, species identification, and climate change impacts on coral reef systems.
Coral bleaching phenomena, triggered by elevated water temperatures associated with climate change, represent one of the most critical threats facing marine ecosystems globally. Fluorescent photography provides researchers with enhanced capabilities for monitoring coral health status, documenting bleaching progression, and assessing recovery potential following thermal stress events. The dramatic visual contrast between healthy fluorescent coral tissue and bleached skeletal structures enables more precise documentation of bleaching patterns and severity levels.
Ocean acidification processes, resulting from increased atmospheric carbon dioxide absorption by seawater, cause progressive dissolution of calcium carbonate skeletal structures in coral organisms. Fluorescent imaging techniques reveal these destructive processes with exceptional clarity, providing researchers with powerful tools for documenting acidification impacts and developing protective strategies for vulnerable reef systems.
Coral propagation research benefits tremendously from fluorescent photography applications, particularly during polyp bailout events where microscopic organisms release reproductive cells into the water column. These nearly invisible reproductive cells become clearly visible under blue light illumination, appearing as brilliant sparkles against dark backgrounds and enabling researchers to document reproductive timing, success rates, and larval distribution patterns.
The remarkable sensitivity of fluorescent imaging techniques has led to discoveries of previously unknown species that remained invisible under conventional white light illumination. These microscopic organisms shine brilliantly under blue light excitation, enabling taxonomists to identify and classify new species that contribute to our understanding of marine biodiversity and ecosystem complexity.
Essential Equipment Requirements for Professional Fluorescent Photography
Successful fluorescent underwater photography demands specialized equipment configurations that differ significantly from conventional underwater imaging systems. The primary illumination source must emit concentrated blue wavelength radiation typically ranging from 440 to 480 nanometers, corresponding to royal blue or actinic light specifications commonly used in marine aquarium applications.
High-quality fluorescent diving torches incorporate advanced LED technology optimized for maximum efficiency within the critical blue wavelength range. These specialized illumination devices often feature dichroic filtering systems that enhance color saturation and eliminate unwanted wavelengths that could interfere with fluorescent emission observation. The dramatic improvement in image quality achieved through dichroic filtration justifies the additional cost and complexity of these advanced lighting systems.
Professional-grade fluorescent photography equipment includes multiple lighting options ranging from handheld torches suitable for macro photography applications to high-intensity video lights capable of illuminating large reef sections for wide-angle imagery. The selection of appropriate lighting equipment depends upon the specific photographic objectives, subject size, working distance requirements, and desired depth of field characteristics.
Advanced practitioners often utilize combination lighting systems that incorporate both continuous blue illumination for composition and focusing purposes along with high-intensity strobe systems equipped with excitation filters for final image capture. This dual-system approach provides maximum flexibility while ensuring optimal image quality across diverse photographic scenarios.
Supporting equipment includes specialized mounting systems, power management solutions, and backup lighting devices essential for safe night diving operations. Professional fluorescent photography expeditions require redundant equipment configurations to ensure dive safety while maintaining photographic capabilities throughout extended underwater sessions.
Critical Excitation Filtering Systems and Optical Considerations
Excitation filters represent essential components for converting conventional white light sources into effective blue wavelength illumination systems suitable for fluorescent photography applications. These specialized optical filters selectively transmit blue wavelengths while blocking unwanted portions of the electromagnetic spectrum that could interfere with fluorescent emission observation.
The fundamental challenge with excitation filtering involves the substantial light output reduction that occurs when filtering white light sources to obtain the desired blue wavelength range. Typical excitation filters reduce overall light output by approximately 80 percent, creating significant challenges for achieving adequate illumination levels especially for wide-angle photography applications.
Dedicated blue LED light sources provide superior efficiency compared to filtered white light systems because they generate the desired wavelength range directly without requiring filtration losses. This inherent efficiency advantage makes dedicated blue lights the preferred choice for serious fluorescent photography applications where maximum light output is essential for achieving optimal results.
Professional strobe systems can effectively utilize excitation filters despite the substantial light reduction because these devices generate extremely high light output levels that provide adequate illumination even after filtration losses. The tremendous power output of professional strobes makes them particularly well-suited for macro photography applications where high magnification ratios demand intense illumination for proper exposure.
Advanced excitation filter designs incorporate sophisticated optical coatings and precision manufacturing techniques that maximize blue wavelength transmission while minimizing unwanted wavelength leakage. These high-performance filters provide superior color saturation and contrast compared to conventional filter systems, justifying their higher cost for serious fluorescent photography applications.
Essential Barrier Filtration for Visual Observation and Photography
Barrier filters represent absolutely critical safety and functionality components for fluorescent diving operations, serving dual purposes of protecting diver vision while enabling proper observation of fluorescent phenomena. These specialized filters mount over diving masks and camera lenses to selectively block blue excitation wavelengths while transmitting longer wavelength fluorescent emissions.
The primary safety function of barrier filters involves protecting diver eyes from potentially harmful blue light exposure that can cause significant discomfort, irritation, and potential vision damage during extended observation periods. High-intensity blue illumination can overwhelm natural vision mechanisms, making prolonged exposure extremely uncomfortable and potentially dangerous for underwater operations.
From a functional perspective, barrier filters solve the critical problem of blue light overwhelming the much dimmer fluorescent emissions generated by marine organisms. Without proper barrier filtration, the intense blue excitation light completely masks the subtle fluorescent colors, making observation and photography effectively impossible despite the presence of fluorescent phenomena.
Professional barrier filter systems utilize precision optical coatings that provide sharp cutoff characteristics at approximately 480 nanometers, effectively blocking blue excitation wavelengths while maintaining excellent transmission of longer wavelength fluorescent emissions. The precise wavelength cutoff ensures optimal contrast between excitation illumination and fluorescent emission while preserving natural color rendition of observed phenomena.
Advanced barrier filter designs incorporate anti-reflective coatings and specialized optical geometries that minimize internal reflections and maintain maximum light transmission efficiency. These sophisticated optical systems provide superior image quality while ensuring comfortable extended observation periods essential for successful fluorescent photography operations.
Comparative Analysis of Blue Versus Ultraviolet Excitation Methods
Two primary excitation methodologies exist for stimulating marine fluorescence phenomena: invisible ultraviolet radiation below 400 nanometers and visible blue light typically ranging from 440 to 480 nanometers. Each approach offers distinct advantages and limitations that influence equipment selection and operational procedures for fluorescent photography applications.
Ultraviolet excitation systems provide the apparent advantage of eliminating barrier filter requirements because the excitation radiation remains invisible to human vision and most camera sensors. This simplification reduces equipment complexity and eliminates the visual acuity reduction associated with barrier filtration systems, potentially improving navigation and safety during night diving operations.
However, comprehensive research has demonstrated that blue light excitation provides significantly superior fluorescent stimulation efficiency compared to ultraviolet radiation, with improvement factors of approximately four times greater emission intensity for equivalent excitation energy levels. This substantial efficiency advantage makes blue light the preferred excitation method for most fluorescent photography applications.
The evolutionary adaptation of marine organisms to underwater light conditions provides biological justification for blue light superiority in fluorescent stimulation. Natural sunlight penetration through seawater results in predominantly blue wavelength illumination at depths beyond 10 meters, creating evolutionary pressure for marine organisms to optimize their fluorescent responses to blue rather than ultraviolet radiation.
Safety considerations strongly favor blue light excitation systems over ultraviolet alternatives due to the immediate visual feedback provided by visible blue illumination. Ultraviolet radiation poses significant eye damage risks because its invisible nature prevents natural protective reflexes including pupil constriction and involuntary blinking responses that normally protect against excessive light exposure.
Surface reflection characteristics of seawater result in approximately 95 percent of incident ultraviolet radiation being reflected rather than penetrating into the water column. The small fraction of ultraviolet light that does penetrate seawater becomes completely absorbed within the first one to two meters of depth, making ultraviolet excitation biologically irrelevant for most marine organisms.
Professional Photography Techniques and Creative Applications
Fluorescent underwater photography encompasses diverse creative approaches ranging from intimate macro documentation to spectacular wide-angle environmental imagery. Each photographic style requires specialized techniques, equipment configurations, and technical considerations to achieve optimal artistic and scientific results.
Wide-angle fluorescent photography often employs light painting techniques where photographers utilize extended exposure times while systematically illuminating reef sections with handheld blue torches. This methodology requires careful coordination between camera positioning, exposure timing, and light movement patterns to create evenly illuminated compositions without photographer shadows or light source artifacts.
Macro fluorescent photography represents the most accessible and rewarding approach for most underwater photographers, providing opportunities to reveal extraordinary detail and coloration in subjects that appear mundane under conventional white light illumination. The dramatic color transformations achieved through fluorescent excitation can transform ordinary subjects into spectacular science fiction-like imagery that captivates viewers and reveals hidden aspects of marine biology.
Video applications for fluorescent photography present unique challenges primarily related to the substantial illumination requirements necessary for adequate frame rates and depth of field. Professional video applications typically require multiple high-intensity light sources and specialized filtration systems to achieve broadcast-quality results while managing the increased visibility of suspended particles that fluoresce along with target subjects.
Advanced practitioners develop personalized lighting strategies that combine multiple illumination sources including continuous blue lights for composition and focusing along with filtered strobes for final exposure. This multi-source approach provides maximum creative control while ensuring technical excellence across diverse subject types and environmental conditions.
Strategic Equipment Selection and Configuration Methodologies
Professional fluorescent photography systems require careful integration of multiple specialized components including illumination sources, filtration systems, camera configurations, and support equipment. The optimal system configuration depends heavily upon specific photographic objectives, operational environments, and budgetary constraints facing individual photographers.
Strobe-based systems offer superior power output and precise exposure control capabilities that prove particularly valuable for macro photography applications requiring maximum depth of field and sharp subject definition. However, strobe systems require additional blue focus lights for target identification and composition because conventional white light focus illumination cannot reveal fluorescent subjects effectively.
Continuous lighting systems utilizing high-intensity blue video lights provide exceptional versatility and real-time composition capabilities that many photographers prefer over strobe alternatives. The immediate visual feedback provided by continuous illumination enables precise light positioning and shadow control that can be difficult to achieve with strobe systems that require test exposures for evaluation.
Camera selection considerations encompass both digital single-lens reflex and compact point-and-shoot systems, with each platform offering distinct advantages for different aspects of fluorescent photography. Professional DSLR systems provide superior lens selection options and advanced exposure control capabilities, while compact cameras offer simplified operation and reduced system complexity that appeals to many underwater photographers.
Essential equipment redundancy requirements include backup illumination sources, spare barrier filters, and emergency white light systems necessary for safe navigation during night diving operations. Professional fluorescent photography expeditions must maintain complete equipment redundancy to ensure both photographic success and diver safety throughout extended underwater operations.
Advanced Camera Configuration and Technical Settings
Successful fluorescent photography requires substantial modification of conventional underwater photography settings to accommodate the unique characteristics of fluorescent emission phenomena. The relatively dim nature of fluorescent emissions compared to reflected sunlight necessitates fundamental changes in exposure strategies, focusing methodologies, and composition techniques.
Aperture priority exposure modes generally provide optimal results for fluorescent photography because they enable photographers to control depth of field while allowing automatic shutter speed adjustment to achieve proper exposure for varying fluorescent emission intensities. Wide aperture settings maximize light gathering capability while potentially compromising depth of field, requiring careful balance between technical and artistic considerations.
ISO sensitivity settings require careful optimization to balance image quality with exposure requirements, as fluorescent emissions often demand elevated sensitivity settings that can introduce digital noise artifacts. Modern camera sensors provide remarkable high-ISO performance that enables fluorescent photography at sensitivity levels previously considered unusable for serious photographic applications.
Autofocus performance in low-light fluorescent photography applications depends heavily upon lens motor speed and focusing algorithm sophistication. Fast-focusing lenses provide substantial advantages for tracking moving fluorescent subjects, while slower focusing systems can prove frustrating when attempting to capture rapidly moving or intermittently visible fluorescent phenomena.
Manual focus techniques offer superior precision for stationary subjects but require exceptional stability and precise distance estimation that can be challenging in underwater environments with current and surge conditions. The shallow depth of field associated with wide aperture settings makes precise focus critical for successful fluorescent macro photography applications.
Operational Safety Considerations and Risk Management
Fluorescent diving operations present unique safety challenges that require careful planning, specialized training, and constant situational awareness to ensure diver safety while pursuing photographic objectives. The modified visual environment created by blue illumination and barrier filtration significantly impacts normal underwater navigation and hazard recognition capabilities.
The substantial reduction in overall visual acuity caused by barrier filtration systems creates potentially dangerous conditions for night diving operations where normal hazard recognition depends upon adequate illumination and full-spectrum vision. Divers utilizing fluorescent photography equipment must maintain heightened awareness of their surroundings and potential hazards that may not be visible under blue light illumination.
Specific marine hazards including venomous fish species that do not exhibit fluorescent properties become effectively invisible under blue light illumination while potentially being attracted to the unusual lighting conditions. Lionfish represent a particular concern because they show minimal fluorescent response while being attracted to the small creatures that blue lights often reveal, creating potential for inadvertent contact.
Emergency lighting procedures require all fluorescent divers to carry conventional white light systems for navigation, safety signaling, and emergency situations. These backup lighting systems must remain easily accessible and regularly tested to ensure reliability when needed for critical safety functions during fluorescent diving operations.
Professional fluorescent diving operations should include comprehensive safety briefings, buddy system protocols, and emergency response procedures specifically adapted for the unique challenges associated with reduced visual acuity and specialized equipment requirements of fluorescent photography diving.
Certification Programs and Educational Opportunities
Specialized training programs provide essential knowledge and practical skills necessary for safe and effective fluorescent diving operations. Professional diving organizations have developed distinctive specialty courses that address the unique technical, safety, and photographic aspects of fluorescent underwater photography.
The Professional Association of Diving Instructors offers a comprehensive Distinctive Specialty certification program covering both fluorescent diving techniques and fluorescent photography methodologies. This specialized course provides in-depth coverage of the scientific principles, equipment requirements, safety procedures, and practical techniques necessary for mastering fluorescent diving applications.
Approximately one hundred certified instructors worldwide possess qualifications to teach fluorescent diving specialty courses, providing global access to professional training programs for interested divers. These specialized instructors have completed advanced training programs and demonstrate practical expertise in fluorescent diving operations and photography techniques.
Educational course content encompasses detailed coverage of marine fluorescence biology, optical physics principles, equipment selection and configuration, safety procedures, and advanced photography techniques specifically adapted for fluorescent applications. Students gain both theoretical knowledge and practical hands-on experience necessary for independent fluorescent diving operations.
Certification programs provide structured learning environments that ensure proper safety training while developing technical competency in equipment operation and photographic techniques. Professional certification represents essential preparation for divers planning to pursue fluorescent photography as a serious underwater imaging discipline.
Environmental Impact and Conservation Applications
Fluorescent photography techniques provide powerful tools for marine conservation research and environmental monitoring programs that contribute significantly to understanding and protecting underwater ecosystems. The enhanced visibility of coral bleaching events, disease progression, and reproductive cycles enabled by fluorescent imaging supports critical conservation research initiatives worldwide.
Coral health assessment applications utilize fluorescent photography to document subtle changes in coral tissue condition that remain invisible under conventional lighting conditions. The dramatic contrast between healthy fluorescent coral tissue and compromised areas enables researchers to identify stress conditions before they become apparent through conventional observation methods.
Climate change research benefits tremendously from fluorescent imaging capabilities that reveal detailed information about coral adaptation mechanisms, bleaching recovery patterns, and long-term ecosystem changes. These documentation capabilities provide essential data for developing effective conservation strategies and predicting future ecosystem changes.
Species identification and biodiversity assessment programs utilize fluorescent photography to reveal cryptic species and document previously unknown organisms that contribute to comprehensive understanding of marine ecosystem complexity. The discovery potential of fluorescent imaging continues to expand scientific knowledge of marine biodiversity.
Responsible environmental stewardship requires fluorescent photographers to minimize their impact on sensitive marine ecosystems while pursuing documentation objectives. Professional practitioners develop sustainable photography techniques that avoid damaging fragile coral structures or disrupting natural behavioral patterns of marine organisms.
Future Technological Developments and Innovation Trends
Advancing LED technology continues improving the efficiency, power output, and wavelength precision of blue illumination systems used for fluorescent photography applications. These technological improvements enable development of more compact, longer-lasting, and more effective lighting systems that expand the practical applications of fluorescent diving techniques.
Camera sensor technology advances provide enhanced low-light performance capabilities that reduce illumination requirements while improving image quality for fluorescent photography applications. Modern sensors offer remarkable sensitivity and noise performance that enables fluorescent photography techniques previously impossible with conventional equipment.
Optical filter technology developments focus on improving transmission efficiency while maintaining sharp wavelength cutoff characteristics essential for optimal fluorescent observation. Advanced coating technologies and precision manufacturing techniques continue improving filter performance while reducing costs for professional fluorescent photography systems.
Underwater housing manufacturers increasingly recognize the specialized requirements of fluorescent photography applications, developing housing designs that accommodate the unique lighting configurations and filtration systems required for effective fluorescent imaging. These specialized housings incorporate features specifically designed for fluorescent photography applications.
Digital image processing techniques continue evolving to optimize fluorescent photography post-processing workflows while maintaining natural color rendition and artistic quality. Advanced software tools enable photographers to maximize the visual impact of fluorescent imagery while preserving scientific accuracy for research applications.
Final Thoughts
Fluorescent underwater photography represents a revolutionary imaging discipline that combines advanced scientific principles with creative artistic expression to reveal extraordinary aspects of marine ecosystems invisible through conventional photography techniques. This specialized field continues expanding through technological advances, improved training programs, and growing recognition of its scientific and artistic value.
The fundamental science underlying fluorescent phenomena provides a solid foundation for understanding equipment requirements, safety considerations, and technical methodologies necessary for successful fluorescent photography operations. Mastery of these scientific principles enables photographers to optimize their equipment configurations and develop innovative techniques for diverse applications.
Professional equipment systems continue improving through advances in LED technology, optical filtering systems, and camera sensor performance that expand the practical applications and accessibility of fluorescent photography techniques. These technological improvements enable more photographers to explore this fascinating imaging discipline while improving the quality and scientific value of resulting imagery.
The growing recognition of fluorescent photography applications for marine conservation research provides compelling justification for expanding training programs and supporting technological development in this specialized field. The combination of artistic appeal and scientific utility ensures continued growth and development of fluorescent photography applications.
Future developments in fluorescent underwater photography will likely encompass improved equipment integration, enhanced training programs, expanded scientific applications, and broader accessibility for recreational photographers interested in exploring this remarkable imaging discipline. The continuing evolution of technology and techniques promises exciting opportunities for photographers willing to explore the extraordinary world of marine fluorescence.