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Light Matters to Life


ZLI Partnerships Improve Animal Welfare and Health.
Animal care specialists and animal care institutions (eg. zoos and aquariums) need to integrate light (a fundamental aspect of biological and mental health) into husbandry and enrichment programs in order to maintain optimal animal welfare. Recognizing the extreme value of aquariums and zoos, ZLI partnerships might entail time, talent or treasure exchanges, with proceeds supporting research scholarships.

Three basic goals guide ZLI’s Animal Care Partnerships:

  • The first is to give animal care providers a point by point route to improving husbandry practices related to light and lighting.
  • The second, is to set photo-biological care on a scientific footing.
  • The third goal, is to utilize the vast knowledge and experience of animal care providers to improve the science of photobiology.

Five Steps:

Light is much more than what comes from a lighting fixture. Here are five clear steps to addressing photobiology concerns:

  • Understand the Animal’s Photobiology
  • Consider Light from an Animal’s Perspective
  • Make Assessments Immediately, Measure Forever
  • Apply Technology Carefully, Move from Passive to Active
  • Set Targets in a S.P.I.D.E.R. Framework

Understand the Animal’s Photobiology

Q.~ What is the Natural History of the Species? 

Know everything about the natural light conditions in an animal’s native habitat, including when and where major events occur. Remember that natural light is both dynamic and very specific, and is conditioned by material elements such as vegetation, soil, water and other animals. Light sources (such as sun, moon, star, atmospheric etc…), habitat (terrestrial or aquatic) and the individual animal are integral with each other, and need to be understood.

Q.~ What specific photo-biological processes are explored in literature?

While not every species has been the subject of research, scientific research is an important place to begin in deciding how light should be handled to maintain sufficient (or exemplary) animal welfare in a zoo or aquarium. ZLI organizes research into nine (9) distinct categories in the ZLI framework. Three general headings (physiology, sensory ecology and integrative biology), each have sub-categories that organize valuable concepts and information regarding relationships of light and life important to the animals in your care. Such information will allow for better answers to questions that will arise, and will be targeted to specific species (and individuals) in managed care.

Q.- Are you Willing to Partner to Produce Needed Research?

The simple question, ‘What light do I buy?’ yields insufficient results to zoo and aquarium missions to maintain optimal animal health and to connect meaningfully with wildlife conservation initiatives. The most important thing, from a photo biological animal welfare perspective, is the understanding of what a specific animal requires in its own terms. This means pursuing science not as a pursuit in itself, as important as that is, but insofar as it discovers appropriate conditions for a particular species. This means measuring light appropriately, and in ways appropriate to the animal itself (organized by the ZLI Framework). Be willing to measure, either in-situ or ex-situ, and animals will be increasingly better cared for in a brighter future.

Consider Light from an Animal’s Perspective

~ Biologically Relevant Metrics are Important!

For most of our lives, we have been taught to measure light as if it were a kind of fuel, where more is better and less is a problem. When considering animals (human too!), it is better to think of light in terms of ranges rather than absolutes. Too much or too little can be a problem. Understanding what and when a certain light condition is appropriate is as important as understanding how much is appropriate.

A second important point is that biologically speaking, light is meaningfully measured either by photon density counts over time for the majority of light related processes, or in certain instances the power of this same electro-magnetic radiation as it is expressed in Watts. Other types of measurements, such as lux, foot-candles, temperature and the like, simply aren’t relevant for biological processes. Results in these later terms from an animal welfare perspective are unhelpful at best, misleading at worst. Measuring properly (using a proper tool (a spectrometer that provides photon count information), is absolutely necessary to pursuing proper animal welfare when we are talking about light.

~Objects/Materials Condition Natural Light

Usually, when we think of ‘light’, we are thinking of ‘light bulbs’ (‘lighting’), or other obviously ’emitting’ sources such as sun, moon, star and the like. Yet the materials that the radiation initially emitted by these sources strike, have as much of an impact on the overall light utilized as a resource by animals as do the initial sources themselves. One way to think of this is to remember the phrase ‘light reflected is light emitted’, and to be as careful in arranging and modifying an animal space with this in mind as one would be in buying a light fixture to hang above or below it.

Another consideration here, is that light reflected by objects that provides visual cues matter as well. An animal’s visual field is highly specialized and a result of selective pressures, cued to very specific indicators in its natural environment. Those objects present in an animal exhibit are essentially visual objects, and while they do not need to replicate natural conditions necessarily, they ought to be considered in reference to such conditions.

~Natural Light Changes Over Time

It is a truism in architectural daylighting, that natural light is preferred over artificial light, because natural light changes over time and is more closely related to how human vision functions. This dynamism is indeed related to how photo-physiology, sensory ecology and integrative biology work. One might think of our own constant eye-movements as a reference (holding eyes still will result in temporary blindness and fatigue as retinal cells cannot ‘reset’). Dynamism also refers not simply to immediate relationships (in terms of seconds, minutes and hours), but also the daily, monthly, seasonal, annual and twelve year stellar cycles found in the natural environment. In biology as architectural daylighting (a bit of a twist for us), the dynamism of natural light is a crucial factor to introduce when possible.

~Natural Light has Shape

Generally speaking, natural light does not come to a point from all directions equally. Light from a horizon might dominate, or from directly overhead. It might be filtered, dappled or diffused in haze. The different shapes of light found in an animal’s in-situ environments impact the evolution of species, and how they utilize such light as a resource over time. In an animal exhibit, recognition of the shape of light (for instance the presence of windows at the horizon) may or may not (depending on the species), play a factor in stress induction or in the availability and/or pursuit of the Five Freedoms.

Make Assessments Immediately, Measure Forever

~ Document Natural Habitat Conditions

As a first step, after the prep work taken in understanding the natural history and existing biological photo-biological research (using the ZLI Framework), it is vital to document such information so that it can serve as a shibboleth for ongoing decision making. This Document should be included in any planning or design guidelines for future projects, in addition to locally maintained husbandry manuals.

~ Adjust Odd/ Inappropriate Shapes of Light

While it has long been a truism that elements such as ‘shade’ or ‘hiding places’ are important to animal welfare, adjusting odd shapes of light goes a bit beyond this. it refers to specifically considering the distribution of light related to the ZLI Framework categories of photo-physiology, sensory ecology and integrative biology (the ways in which light conditions the timing, distribution and epidemiological productivity of animals).

The latter category might be the most difficult to appreciate at first glance, but it refers simply to the fundamental problem of night lighting, which serves as a disease enhancing vector in managed populations, by attracting disease bearing insects to locations and in concentrations that they would not normally be in. This is a challenge in the ‘shape’ of light, as we are describing it, and one immensely related to animal welfare of animals in managed care.

~Manage Incident Point Sources to Reduce Glare / Stress

How often, do we hear the phrase ‘a deer in headlights’? For a white-tail on a road frozen in front of speeding car, the tragic results are obvious. Yet, when we apply artificial light in an aquarium or zoo, the tragic results can be far less obvious and spread out over time. It is important to recognize that the introduction of constant glare (like a neighbor’s porch light shining through a window at night), introduces stress by applying a kind of constant pressure into that same environment.

Incident light sources, whether unintentional such as exit light LEDS or intentional such as immobile theatrical exhibit spot-lighting, in general do not move and depending on direction and intensity, can result in a variety of health effects such as cataracts and effective blindness. Although such point sources might very well introduce other deleterious factors in terms of specific photo-biological impacts, the difference in intensity between such sources and surrounding light conditions can be particularly problematic for animal eyes, which always adjust to the brightest area of the visual field to the functional detriment for the whole.

~Eliminate Inappropriate Flicker

Flicker refers to the rapid, regular changes of intensity emitted by an electric light fixture. It is measurable, and often noticed when taking video due to differences in the flicker rate and frame rate of the camera. Certain flicker rates have been connected to photo-sensitive epilepsy, migraines and Méniére’s Disease in humans.

While guidelines for specific flicker rates and their impact on individual species are in general not available, a guideline to follow is to eliminate lighting with a flicker rate of less than 100 HZ in any animal space. While a much higher rate is to be preferred, this action ought to be taken immediately.

~ Measure (using Spectra-radiometer & Digital Camera)

The Sciences of Light and Life, and indeed most science, require instruments to collect data not immediately apparent to the eye. While the required tools depend upon the desired data, two tools are indispensable. A spectro-radiometer aids an animal care specialist in determining what relevant light conditions exist, giving diagnostic information about the animal and its environment over time. A digital camera, particularly one equipped with a fisheye lens and having UV sensitivity, allows for general reconstruction of the shape of light in the luminous environment.

Measurements must be taken regularly over time, as an integral part of an enrichment program (ex-situ lighting could never be the same as in-situ lighting conditions, and so lighting can be thought of as a kind of enrichment to address such differences).

~Record Measurements to Collate Data for Assessments

Existing photobiology science is incomplete. The ZLI Framework offers guidance as to potential arenas for various subjects, and ZLI’s goal is to engage science friendly zoos and aquariums to enhance such understanding, as comparative research cannot happen elsewhere but where such animals are managed in constant care. Data collection and coordination is necessary, to build viable samples from which better understanding can be developed and better decisions can be made.

Apply Technology Careful, Move from Passive to Active

Utilize S.P.I.D.E.R. Protocols for All Artificial Light

Target Specific ZLI Framework Categories

Proceed from Passive to Active Strategies

Measure Incident Light in Ongoing Commissioning Program

Set Targets:

Data Collection 

A+ Automated Reporting of Continuous (hourly) Readings 

A Reporting of Bi-Monthly Conditions (hourly) (New and Full Moon)


1. Collate In-situ and ex-situ assessments / measurements 

2. Establish Process Targets with Diagnostic Assessments

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