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National Research Council (US) Institute for Laboratory Animal Research. The Development of Science-based Guidelines for Laboratory Animal Care: Proceedings of the November 2003 International Workshop. Washington (DC): National Academies Press (US); 2004.

Cover of The Development of Science-based Guidelines for Laboratory Animal Care

The Development of Science-based Guidelines for Laboratory Animal Care: Proceedings of the November 2003 International Workshop.

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Breakout Session: Lighting

Leader: Harry J. M. Blom

Rapporteur: Michael K. Stoskopf

The session leader posed the following questions to the group:

What is the scientific basis or peer-reviewed literature for housing standards for laboratory animals? What other (if any) influences or factors are involved?

General consensus was quickly reached among the participants that the scientific basis for housing standards for laboratory animals is uneven, with large areas that lack adequate investigation. Some concern was expressed that not all “scientific” information is sufficient for development of standards. Participants stressed the care in design and execution of experiments, including the need for replication and proper controls necessary to provide reliable information. In addition, scientific design and replication of studies varies: One poorly designed study can dictate standards inappropriately.

The moderator posited that the influences on standards, other than peer-reviewed scientific data, include daily practice, common sense, and prevailing expert views. It was suggested that it might be appropriate to establish standards. The group allowed that although these factors do become the basis of standards, there are important concerns with this approach, and the development of standards without scientific basis is fraught with the peril of inappropriate regulation. These concerns were expressed first in a question related to expertise and second in the subsequent brief discussion of common sense.

Who determines the prevailing expert view?

Participants indicated that individuals with different backgrounds can have diametrically opposed biases on appropriate prioritization of the various concerns. In addition, they felt that giving unfounded dogma official sanction can retard proper scientific examination of the viewpoint. Similarly, some expressed the opinion that common sense can frequently be wrong. Individuals may tend to express anthropomorphic views basing judgment of other species, needs on human senses and needs, and this may not always be appropriate.

Although it is necessary to have some basis for a starting point, participants felt it would be optimal if the starting point were based on scientific evidence.

Where are the gaps in our scientific knowledge? Is the information missing? Is it outdated?

Discussion of these questions was divided into three areas related to light: (1) intensity, (2) periodicity, and (3) transitions, including “flicker detection.”


Issues related to light intensity were organized into the following three categories for discussion: (1) satisfaction of biological requirements, (2) safety and efficiency of people working in the room, and (3) effects of excessive exposure. All three areas have gaps in knowledge.

Biological requirements related to vitamin synthesis have been determined for some species; however, less is known about intensity requirements relative to neuroendocrine function, especially across a broadly comparative group of laboratory species. The safety and efficiency of people working in the room have been studied more than the preceding category, but often in studies unrelated to laboratory animal care. Human effectiveness and its variability under different lighting conditions are relatively well studied. Much of the discussion focused on the issue of effects of exposure to excessive intensity, with particular focus on light that is too bright and causes blindness or retinal lesions in some species. Very bright light should be avoided for some species (e.g., albino rodents, as recommended in the Guide reference to 30 to 50 foot-candles), and darker areas should be available to the animals. With regard to the needs of other strains and species, participants stated that tiered cages and the location in the tier are factors that have not been considered, because most studies have looked at average room conditions.

Some time during this session was devoted to determining how different institutions are dealing with light intensity challenges. Mentioned were manufactured lenses covering fluorescent bulbs to reduce lighting to within range; removal of some of the bulbs commonly used for lights in ceiling, but not with uncovered tops on racks; and the practice of rearing animals in the dark (e.g., use of transgenics) in ophthalmology studies. Participants expressed concerns regarding potential damage caused by light intensity that is too low (e.g., on the retina).


Dr. Blom suggested starting with the following areas, in which the knowledge base is well established:

  • Providing regular photoperiods;
  • Avoiding interruptions of those periods;
  • Considering low-level night lighting; and the
  • Potential importance of the duration of the light/dark cycle, for the manipulation of reproductive cycles in breeding and related research.

The group did not take exception to those points, but discussed that periodicity and particularly the duration of light/dark cycles is important for many other things besides reproduction.

Much of the discussion centered on experiences with nocturnal animals such as owl monkeys. There is still more to be understood about the use of simulated moonlight (lower intensity vs. spectral shifts) across species. Simulated moon light is being practiced in some of the forms, but has proven impractical for allowing workers to properly clean and manage rooms and adaptation to the low levels (about 10 lux), For this reason, it does not appear to be effective. The main solution to the problem created by workers being required to turn on the lights appears to be creative shifts of time reversal so that “daylight” exposures occur during working and cleaning, and “dark” periods are reserved for observation periods.

The important point was stressed that this issue is more refined than simply identifying the light/dark cycle. The cycle can affect results for many types of studies such as metabolism, for which considerable data exist. In addition, it has been shown that seasonal shifts in diurnal cycles can be crucial.

The group identified an important need for better reporting of husbandry and procedures in published papers to allow evaluation and replication of the studies. It is hoped that online publishing will help resolve this problem, but participants recognize that a strong demand for complete disclosure of husbandry, including light management, is needed.


Our knowledge of the impact of transitions is weak, but we have reasonable scientific basis from field studies to consider that they may affect research outcomes and perhaps animal wellness. Rapid transitions will invoke alarm behaviors in several species, and the metabolic impacts of these transitions are poorly understood. Although considerable effort has been invested in managing diurnal cycles in some species and facilities, much less effort has gone into managing transitions. One possible challenge has been the wide spread use of fluorescent lighting, which requires relatively expensive electronics to dim. Those devices have also recently been shown to produce ultrasound at levels that could be problematic. The consensus of participants is that expense was the main driving force in the use of fluorescent lighting, and this in turn has resulted in limited options in light management.


Dr. Blom posed the possibility that rodents could use red light during their active phase, which would also constitute a good approach for balancing the need for humans to see during the active phase. In this context, participants indicated the existence of gaps in the following areas:

  • The effect of red light;
  • Whether blue light is more appropriate for nocturnal periods;
  • The need to identify the ultraviolet (UV) requirements of various species (already known for some reptiles, birds, and insects, but largely extrapolated across mammals); and
  • Whether animals need exposure to a spectrum of full daylight.


The issue of flickering was discussed because of challenges identified in Europe. Because 50 Hz is used as the typical cycle for power in Europe, fluorescent bulbs flicker at 50 Hz, rather than at 60 Hz, the cycle commonly used in the United States. The critical fusion frequency for an individual or species is the frequency at which a cycling light would be perceived as a continuous light source. The higher the critical fusion frequency of a species, the more likely they would be to perceive a fluorescent light as flickering on and off rather than providing steady light. This problem also occurs in humans and is the basis of considerable investigation relative to impacts on health and well-being. For cats, the critical fusion frequency is known to be slightly >50 Hz. For birds, the problem may be more acute because birds have a fourth type of cone that is sensitive to UV light and is phasic (i.e., sensitive to flickering up to 110 Hz).

Some participants suggested that potential problems from flicker perception should be studied in laboratory species. Others identified additional problems from fluorescent lights including generation of ultrasound by ballasts.


Among the many knowledge gaps related to light and laboratory species, the following areas clearly require additional information:

  • Knowledge of species and strain variations in susceptibilities and needs;
  • Natural history studies with communication to laboratory animal scientists (e.g., metabolic shifts, behavioral endocrine shifts);
  • Photoperiodicity studies;
  • Light acuity sensitivity data;
  • Studies on the effects of maintaining rodents under dim light with periods of increased light intensity; and
  • Studies of the effects of cage materials (e.g., clear vs. tinted walls) at actual light levels experienced in the cage itself (secondary enclosures) as opposed to the room.


Some participants felt that it is possible to spend so much time and effort on a particular engineering standard that time working with animal enrichment is severely decreased. Participants identified prioritization of effort as an important issue.

Similarly, it was felt that engineering standards can create important problems if based on poor data. This problem occurs particularly when engineering standards are too tightly defined and result in retarding the generation of new knowledge. It is common for engineering standards to conflict with performance standards.


“Shoulds” tend to evolve into “musts.” There is a strong need for the use of adaptive management in many laboratory animal maintenance situations. In the absence of knowledge, the freedom to experiment and explore options is required. Participants indicated that investigators should be encouraged to study the effects of husbandry on their research.

It is possible for IACUC chairs to prefer strong and narrow regulations with tight interpretations to facilitate their ability to exert control over investigators who are not in optimal compliance. That approach, of functioning as a policeman and an enforcer, is one alternative; however, the approach of working with investigators as part of a team to improve animal welfare and care seems to be more effective.


This issue was not addressed during the session in detail because of time constraints, but the general position of the participants was to embrace performance-based standards in preference to specific engineering standards. This position was based largely on the perceived need to address a wide range of species and strains that may have different needs. Also of concern was the need to balance the lighting needs of animals with those of staff who are attempting to maintain the colony or conduct research.

Copyright © 2004, National Academy of Sciences.
Bookshelf ID: NBK25433


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