Ya. E. Neishtadt

Erythemal Fluorescent Lamps

From the Erisman Scientific Research Institute of Sanitation

The use of fluorescent lamps whose spectrum includes ultraviolet radiation alongside visible light is a matter of great importance for hygiene.

The hygienic requirements for solar fluorescent lamps were set out in our report to the First Plenary Session of the Committee on Lighting Hygiene of the USSR Academy of Medical Sciences in May 1947.

For erythemal lamps to be widely adopted, their ultraviolet output must be standardized.

In 1950, when the Lighting Engineering Commission of the USSR Academy of Sciences was drawing up technical specifications for the manufacture of solar lamps, it provided only a general stipulation: the ratio of luminous to erythemal flux should deliver 0.1 erythemal dose during 8 hours of daily exposure at an illuminance of 300 lux.

In our view, the regimen for using both solar fluorescent lamps, which emit visible light and ultraviolet radiation, and erythemal lamps proper, which emit predominantly erythemal radiation, should be based on studies of solar ultraviolet radiation at different latitudes.

To address this problem, long-term observations of solar ultraviolet radiation in Lenin-

…grad, the results of studies of solar ultraviolet radiation in Kazan and Saratov, and, for the middle latitudes, our data on Moscow’s “ultraviolet climate.”

From April 1948 through December 1951, regular systematic observations of solar ultraviolet radiation in central Moscow were conducted at the Erisman Scientific Research Sanitary Institute, using the decomposition of oxalic acid in the presence of uranyl salts. Radiation in the ranges \(2,900\)–\(4,000\) Å and \(2,900\)–\(3,500\) Å was studied on irradiated horizontal and vertical surfaces.

Since September 1949, in parallel with these observations, regular measurements of solar ultraviolet radiation have been made using an antimony–cesium photocell with a UFS-1 filter, which records all ultraviolet radiation reaching the Earth’s surface. These measurements continue at present.

During the summer months of 1951, we also made more than 450 measurements with an ultraviolet meter of the All-Union Power Engineering Institute, using a magnesium photocell to measure the specifically erythemal region of the solar spectrum.

The magnesium photocell makes it possible to measure solar ultraviolet radiation in absolute units.

The results of our four years of observations show that, in the middle latitudes, the intensity of solar ultraviolet radiation from November through January is extremely low. It should be emphasized in particular that on many days during these months ultraviolet radiation is almost entirely absent. Even on days when radiation is present, many hours outdoors are required to receive a prophylactic dose.

It should also be borne in mind that during the winter months the exposed surface of the body subject to irradiation is considerably reduced. Whereas in spring and summer it constitutes approximately 11–12% of the total body surface, in winter it barely reaches 5–7%, and the irradiated area does not exceed \(0.1\ \mathrm{m}^2\).

All this confirms the need for the systematic use of sunlamps and erythemal fluorescent lamps, especially during periods when solar radiation is absent or when, owing to the working and living conditions of different population groups, exposure to it is insufficient.

In the middle latitudes, the use of erythemal fluorescent lamps is recommended from October through March. Their use in April and September should be limited. There is no need to use erythemal lamps from May through August.

Alongside the regimen of use, it is necessary to determine the level of ultraviolet radiation in erythemal lamps.

In setting a standard for the daily level of ultraviolet radiation from erythemal lamps, we start from the requirement that \(1/8\) (\(0.125\)) of a prophylactic erythemal dose be received each day.

Because the use of erythemal fluorescent lamps in luminaires will limit the extent to which their erythemal flux can be fully utilized, and because the exposed surface of the body is reduced during the winter months, we increase the stated dose by a factor of \(1\frac{1}{2}\).

As our studies show, one eighth (\(0.125\)) of an erythemal dose amounts to \(500\ \frac{\mu\mathrm{W}\cdot\mathrm{min}}{\mathrm{cm}^2}\). With daily exposure averaging 5 hours, to obtain a prophylactic antirachitic dose (\(0.125\cdot 1.5\)), the lamps must produce erythemal radiation at an intensity of \(0.25\ \frac{\mu\mathrm{W}\cdot\mathrm{min}}{\mathrm{cm}^2}\).

The permissible level of radiation from erythemal lamps should be determined with regard to their intended use.

When erythemal lamps are used in homes alongside fluorescent lamps in general-lighting fixtures, the latter are positioned no more than 1 m above average human height (170 cm). In public buildings, erythemal lamps can be positioned considerably higher.

Clearly, in developing and planning the manufacture of erythemal lamps, our industry should aim to produce at least two types with different radiation intensities.

In addition to their use for prolonged irradiation, erythemal lamps will find application in short-duration irradiation in photaria, in individual irradiation, and elsewhere. The radiation intensity of erythemal lamps intended for short-duration use may exceed the values we have calculated.

In evaluating the hygienic properties of erythemal lamps, we considered it necessary to study first those designed for prolonged use at a distance of 1–1.5 m.

In 1951, we conducted a hygienic evaluation of two batches of erythemal fluorescent lamps manufactured in Moscow, later working jointly with G. A. Smirnov.

In appearance and dimensions, these lamps do not differ from 15 W daylight fluorescent lamps. The tube of the erythemal lamp is made of uviol glass.

The spectral characteristics of the lamps show that they emit primarily in the erythemal region of the ultraviolet spectrum (2,800–3,200 Å). Some of the radiation, however, falls in the 3,200–3,500 Å region of the spectrum.

We measured the radiation intensity of the erythemal lamps using an ultraviolet meter developed by D. A. Shklover, which employs an antimony–cesium photocell with a set of filters as its detector.

Some results of the study of the erythemal effect of the lamps are presented in Table 1.

Table 1. Erythemal effect of the lamps

As follows from the foregoing, erythemal lamps should not cause erythema when operated for 5–6 hours.

In determining the threshold for the erythemal effect, it was established that erythema develops at an exposure of \(4{,}000\ \frac{\mu\mathrm{W}\cdot\mathrm{min}}{\mathrm{cm}^{2}}\). This value differs among individuals and ranges from \(3{,}500\) to \(4{,}500\ \frac{\mu\mathrm{W}\cdot\mathrm{min}}{\mathrm{cm}^{2}}\) in adult men and women.

However, determination of the threshold for the erythemal effect of the lamps must be preceded by determination of their photophthalmic effect. For practical use, only a level of erythemal irradiation that causes no painful symptoms in the mucous membrane of the eye can be accepted.

We determined the thresholds for the photophthalmic effect of erythemal lamps in 7 rabbits (4 white and 3 gray) (Table 2).

Table 2. Photophthalmic effect of erythemal lamps

The threshold for the photophthalmic effect is \(2{,}600\)–\(3{,}000\ \frac{\mu\mathrm{W}\cdot\mathrm{min}}{\mathrm{cm}^{2}}\).

Alongside determining the thresholds for the erythemal and photophthalmic effects of the lamps, we studied their influence on the central nervous system. For this purpose, the threshold light sensitivity and electrical sensitivity of the eye were investigated.

To this end, irradiation with erythemal lamps was carried out either before or during the determination of light sensitivity. The exposed surfaces of the arms and back, comprising an area of approximately \(730\ \mathrm{cm}^{2}\), were irradiated.

The results of the light sensitivity measurements are presented in the figure.

As the figure shows, irradiation with fluorescent erythemal lamps for 1 hour, performed immediately before the light sensitivity thresholds were determined, has a stimulating effect for some time, increasing sensitivity.

However, sensitivity decreases noticeably after only 10 minutes at low ultraviolet radiation intensity and after 5–7 minutes at medium and high intensities. This indicates that ultraviolet radiation at the doses we used has a depressant effect on the central nervous system.

Approximately similar results were obtained when irradiation with erythemal lamps was carried out directly during dark adaptation.

The study of light sensitivity suggests that the ultraviolet flux of the experimental erythemal fluorescent lamps, when used at a distance of no more than 1 m, is somewhat above the permissible level. The intensity of ultraviolet radiation in lamps intended for prolonged irradiation in rooms no more than 3 m high (in dwellings, etc.) should therefore be reduced.

Light sensitivity under exposure to erythemal fluorescent lamps (data averaged over 3–6 days of testing for each series).

Vertical axis: \(\varepsilon\). Horizontal axis: Time since the beginning of dark adaptation, in minutes.

1—without irradiation; 2–3–4—irradiation at different doses.

Determination of optical chronaxie also indicates that irradiation, even at levels up to \(1/8\) of an erythemal dose, is not without effect on the body.

This is consistent with the results of the study of the lamps’ photo-ophthalmic effects.

The next part of our research, conducted jointly with E. V. Dianova, characterized the bactericidal action of erythemal lamps. Since their spectrum lacks the specifically bactericidal radiation of mercury, the bactericidal action of erythemal fluorescent lamps must be attributed to other regions of the ultraviolet spectrum.

The bactericidal action was tested by irradiating a culture of white staphylococcus inoculated onto agar plates. The results are presented in Table 3.

Table 3. Bactericidal action of erythema lamps
(\(J\) from 25 to 38 \(\dfrac{\text{µW}\cdot\text{min}}{\text{cm}^2}\))

As the table shows, after one hour of irradiation, and especially after two to three hours, the number of colonies grown on the plates decreases appreciably. However, a decrease is observed only at an irradiation dose of at least \(25\ \dfrac{\text{µW}\cdot\text{min}}{\text{cm}^2}\). When the lamps are moved to a distance of 1 m, no decrease is observed (figures not shown).

Alongside the studies described above, systematic observations were conducted in our laboratory for more than four months on a group of rabbits exposed over a prolonged period to fluorescent erythema lamps. Their weight gain and blood alkaline phosphatase levels were measured.

The difference in weight gain between irradiated and non-irradiated animals after four months of irradiation is shown in Table 4.

Table 4. Animal weights (g)

The phosphatase findings were more favorable in the irradiated rabbits.

The general appearance and well-being of the irradiated animals were also somewhat better than those of the controls.

Conclusions

1. Domestic industry has developed fluorescent erythema lamps, the production of which is of enormous importance for health promotion.
2. According to approximate calculations, the erythemal radiation dose should be \(0.25\ \dfrac{\text{µW}\cdot\text{min}}{\text{cm}^2}\) when erythema lamps are used for prophylactic purposes.

1. The lamps produced should be tested for their effects on humans, particularly on the central nervous system.

2. The fact that erythemal fluorescent lamps have some bactericidal action makes their widespread use even more valuable. Their bactericidal action should be tested against the natural microflora present in indoor air.

3. It would be desirable to modify the color of erythemal lamps and eliminate the excessively “cold,” bluish light they emit.

4. Alongside the mass production of erythemal lamps, the development and manufacture of solar fluorescent lamps should be accelerated. These lamps should be designed for prolonged use as sources of both illumination and ultraviolet radiation.

5. Erythemal fluorescent lamps intended for widespread use, particularly in medical and childcare institutions and schools, should be supplied with brief instructions for use indicating the levels of erythemal radiation at various distances from the lamp.

These instructions have been developed at the Erismann Scientific Research Institute of Sanitation.