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The Effects of Light on Children
by Warren E. Hathaway, et al.
This study was initiated, funded and distributed by Policy and Planning, Branch Planning and Information Services Division, Alberta Education, 11160 Jasper Avenue, Edmonton, Alberta T5K OL2--February, 1992
Yes. The quality of indoor lighting clearly affects people and this is a report about some of these non-visual effects. It is not a report about particular brands of lights or lighting systems. Although the lights used to create the lighting environments needed for this study were selected with great care, the fact is that these lighting environments could have been created in a variety of ways.
More recently, research has found that variations in the quality of light can significantly influence students in classrooms-- especially, trace amounts of ultraviolet light can serve as a preventative measure in controlling the development of dental caries. Some of the most recent research is described here.
Research points to a number of non-visual effects of light on people. Of these effects the suntan effect and the control of rickets are two that are quite well understood. Other important (but perhaps less well known) effects include: seasonal affective disorder (SAD), synchronization of a number of physiological rhythms, and the control of infantile jaundice. Though artificial lighting systems provide illumination equivalent to only one or two percent of the intensity of daylight, research also suggests that variations in the quality of artificial light in classrooms can have an effect on students.
The photobiologic action spectra of greatest importance to humans ranges from 290 to 770 nm. Skin reddening and vitamin D synthesis occurs in the range of 290 to 315 nm. Tanning or pigmentation of the skin and reduction of dental caries occurs in response to band light in the band from 280 to 400 nm. Vision is most sensitive to light in the 500 to 650 nm range (yellow-green light). Bilirubin degradation occurs in response to light in the 400 to 500 nm range (blue light). Natural light provides the spectral energy distribution necessary for all of these biological functions. Full-spectrum fluorescent illumination also provides substantially all of the spectral energy distribution although light levels are much lower than daylight levels. The spectra of incandescent, cool-white fluorescent, and high pressure sodium vapor light sources appear to fall short of covering the entire photobiologic action spectra of importance to human beings.
For people who are outdoors for a significant part of each day, the quality of indoor lighting to which they are exposed may be of little consequence. Their needs for natural light stimulation may be adequately met.
But for people who spend almost all of their time indoors, and with outdoor exposure limited to morning and evening light, there may be a need for artificial lighting that is supplemented with light stimulation in the spectrum areas of energy deficiency especially blue (440 to 440 nm). Wurtman (1985: xi) very articulately describes the need for clear policy- making guidelines and better understanding of light and its effects on people by first posing a question, Should limits be placed, based on health considerations, on the artificially illuminated lighting environments under which people may live and work?
A Summary of Significant Research Findings
Alberta's Light Study 1987-1991
The study was designed on the basis of a pre-test/post-test, multiple group model and designed to test the null hypothesis:
Different light types (full-spectrum fluorescent, full-spectrum fluorescent with UV enhancement, cool-white fluorescent, and high pressure sodium vapor) have no differential effects on Division II students' dental histories, growth and development histories, vision histories, scholastic achievement histories, or attendance histories when compared over a two-year period.
A number of different types of data were collected from the students including: age, sex, dental histories, nutrition histories, general health, growth and development histories (age at onset of menarche, height, weight, body fat, skin types), vision histories, attendance histories, and scholastic achievement histories.
The study points to significant differences between lighting types when it comes to development of dental caries, gains in height, gains in weight, gains in body fat, gains in achievement, and improvements in attendance as being related to classroom lighting types. Specifically it was found that:
The effect on children of receiving trace amounts of UV radiation in their classrooms amounted to 1.75 fewer caries (cavities) per child per year than was the case in the non-UV schools.
Children exposed to high pressure sodium vapor lighting were absent 3.2 days per year more than students under full spectrum and full-spectrum with UV enhancement.
Gains in body height, weight, and body fat were also significantly linked to lighting systems.
Scholastic achievement was significantly linked to light. Students exposed to high-pressure sodium vapor lighting demonstrated the poorest rate of achievement.
To develop attendance histories monthly attendance was recorded for each student in half day increments and then divided by the maximum number of days the schools were open in order to derive the percentage of attendance. The findings are presented in Table 4.7.
A two-tailed t test comparison of rates of attendance (attendance rates represent the actual attendance divided by possible days for the period September 1987 to June 1989). Levels of significance beyond the 0.05 level are in color.
Site 1 Site 2 Sites 3/5 Site 4 Mean 0.943 0.962 0.959 0.959
St Dev 0.051 0.016 0.038 0.040
N 67 36 136 56 Site 1 (HPSV) 0.943 0.051 67 --- 2.780 2.260 1.933
Site 2 (FS) 0.962 0.016 36 --- 0.707 0.497
Sites 3/5 (FS+UV) 0.959 0.038 136 0.000
Site 4 (CW) 0.959 0.040 56 ---
A number of significant differences in attendance are to be noted. Site 2 (full spectrum) and Sites 3 and 5 (full spectrum with UV supplement) had significantly better attendance than Site 1. The difference amounts to approximately 3.2 days per year. One might conclude that an absence of 3.2 days is about the length of time that it would take to recover from a severe cold.
On the basis of an analysis of attendance records for the children located in the different lighting environments examined in this study, the null hypothesis was rejected--light does have an effect on attendance rates.
One measure of general health which was collected at the study sites was gains in height (measured in centimeters). The smallest gains in height were made at Site 1 (high pressure sodium vapor) while the greatest gains were made at Sites 3 and 5 (full spectrum with UV supplement). Indeed, the gains at Site 1 were significantly less than gains at Sites 3 and 5 (full spectrum with UV supplement) and Site 4 (cool-white).
When Analysis of covariance was applied to the data collected by administering the Canadian Test of Basic Skills in this study, significant differences beyond the 0.05 level were found in total achievement gains (p=0.000, F=11.423) and in gains in language (p=0.003, F=4.877), work study (p=0.040, F=2.826), and mathematics (p=0.001, F=5.912) between the four groups formed on the basis of classroom lighting (i.e., high pressure sodium vapor, full spectrum fluorescent, full spectrum fluorescent with UV supplements, and cool-white fluorescent).
The lowest achievement gains are to be found at Site 1 while the greatest gains are found at Site 2 and Sites 3 and 5.
A two-tailed t test comparison of total achievement gains (combined sub scores on Canadian Test of Basic Skills) measured in grades between June 1987 and June 1989). Levels of significance beyond the 0.05 level are in color.
Site 1 Site 2 Sites 3/5 Site 4
Mean 1.61 2.25 1.96 1.88 St Dev 0.70 0.37 0.45 0.4 N 43 34 109 34 Site 1 (HPSV) 1.61 0.70 43 --- 5.089 3.008 2.101 Site 2 (FS) 2.25 0.37 34 --- 3.737 3.901 Sites 3/5 (FS+UV) 1.96 0.45 109 --- 0.976 Site 4 (CW) 1.88 0.40 34 --- Conclusion
On the basis of an analysis of achievement records for the children located in the different lighting environments examined in this study the null hypothesis was rejected--light does have an effect on rates of achievement.
Putting the Findings into Perspective
Lighting systems are most often designed with efficiency in mind--the objective being to obtain the highest possible lumens/watt ratio. Seemingly little attention is paid to any nonvisual effects lights may have on the occupants using the lighting systems. Clearly, this study points to the single conclusion that no matter how efficient lighting systems are, they are not neutral with respect to their effects on people. Indeed, it appears to be the case that there are a number of non-visual effects associated with lighting systems. This study has identified a number of such effects differences in the rate of dental caries (cavities) development, differences in rates of attendance, differences in the age of the onset of menarche, differences in height, weight, and body fat gains, and differences in scholastic achievement. One might conclude from these findings that natural light is important to the development and well-being of people and to imprison people in spaces lit only with artificial lights designed solely for efficiency amounts to a clear case of daylight robbery.
The relationship of light to the physical well-being and health of people is not surprising. Nor are the effects of color surprising. Blues of the sky, the greens of vegetation, and earth tones are part of our natural environment. It seems reasonable that most people will be most comfortable and relaxed in environments that most closely simulate these conditions.
Natural light provides the spectral energy distribution necessary for all of these biological functions. Likewise, full-spectrum fluorescent illumination provides substantially all of the spectral energy distribution although light levels are much lower than daylight levels. The spectra of incandescent and cool-white fluorescent sources appear to fall short of covering the entire photobiologic action spectra of importance to a human being.
For people who are outdoors for a significant part of each day, the quality of indoor lighting to which they are exposed may be of little consequence. Their needs for natural light stimulation may be adequately met. But for people who spend almost all of their time indoors, as in most office jobs, and with outdoor exposure limited to morning and evening light, there may be a need for artificial lighting that is supplemented with light stimulation in the spectrum areas of energy deficiency--especially ultraviolet in the 280-400nm range.
While high doses of UV light may contribute to health-related problems, the doses received from the lights of this study from an 8 hour day are the equivalent of less than 15 minutes in the sun. This level is well within the ranges recommended as healthy for most individuals.
and Cost Savings Benefits
One of the clear benefits that could derive from applications of this research into the learning environments children occupy could be reductions in the development of dental caries. The benefits of this action would accrue to parents in the form of reduced dental bills. The second clear benefit derives from the fact that under improved lighting conditions students seem to learn better (i.e., demonstrate better academic achievement) and their attendance improves--students are occupying the spaces provided for them (i.e., improved attendance) and they are learning more. The combined effects of these two benefits clearly accrues to the educational institution.
Based on the 1981 to 1985 research it was concluded that there could be significant benefits for education in several areas. On the basis of the daily per pupil educational expenditure in 1984-85 (i.e., $21.42 per pupil space per day) and a with difference of 9.49 days of absence per year for students under different lighting systems, the cost of having these spaces vacant because of these absences amounts to $203.28 per pupil per year (i.e., an average expenditure of $203.28 is made to provide a pupil space which is not used). On the basis of the reduced dental caries, a further saving was calculated at $ 116.75 per pupil per year. Combined, these benefits total $320.03 per pupil per year.
Inasmuch as the cost of providing trace amounts of ultraviolet in classrooms amounts to no more than $30.00 per student per year, there is a net social benefit of $290.03 per pupil per year. It was further concluded that if these benefits could be generalized to all students in Alberta (approximately 430,000) the net social benefit would approach $125,000,000 per year. Moreover, these findings may be generalizable to other regions of Canada, the northern United states, areas frequently shrouded in fog, and other geographical locations where the daily availability of natural ultraviolet light is minimal for extended periods of time.
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