Electric Lamps Producing Energy In The Visible And Ultra-violet Ranges

Abstract

Electric lamps having spectral radiation characteristics approximating natural daylight with a controlled amount of energy in the near and middle ultraviolet ranges which also produce light of sufficient intensity and proper color to make them usable as general illuminants.

Parent Case Text

This is a continuation of application Ser. No. 654,148, filed July 18, 1967, and now abandoned.

Description

As is known, existing illuminants for general use have very distorted spectra in the visible as well as the ultraviolet wavelength ranges when compared to natural daylight. This is shown in Table I below which lists values of color, color rendering index (CRI), color temperature, and ultraviolet output per lumen for typical sources heretofore available. ##SPC1##

In Table I, the following definitions apply to the column headings:

x and y are the coordinates on the standard chromaticity diagram of the ICI (International Commission on Illumination) also known as the CIE (Commissione International De Clairrage)

Cri is the so-called color rendering index adopted by the CIE which measures the color properties of a source related to the corresponding color temperature of a black body radiator or natural daylight. Generally, the number 100 represents the reference illuminant (black body or daylight), so the closer the CRI to 100, the more accurate a match to the reference illuminant the light source has. This is described in "Interim - Method of Measuring and Specifying Color Rendering of Light Sources", Illuminating Engineering, Vol. LVII, No. 7, p. 471 (July 1962)

Color Temperature -- The temperature at which light from a complete radiator (black body) matches in chromaticity the light from a given source

Middle UV -- the ultraviolet portion of the spectrum of natural daylight in the range of 290-320 nm. (nanometers)

Near UV -- the ultraviolet portion of the spectrum of natural daylight in the range of 320-380 nm.

Uv microwatts/lumen -- the amount of ultraviolet energy present per lumen of light output of the source. The values on the Table in parenthesis () are estimated and are extrapolations from the standard, black body, temperature curve locus.

The values listed in Table I are for typical lamps which are commercially available. While there may be some variance in the values given, due to manufacturing and material differences, the listed values are believed to be typically representative of the various types of sources.

As seen from Table I, none of the general types of prior art illuminants listed match natural light in all of its characteristics. For example, the so-called "daylight" fluorescent lamp, which is the only source specifically designed by the lighting industry to match natural daylight, matches it only with respect to color temperature, that is, there is a phase of daylight having a color temperature of the daylight lamp; though only rarely the same chromaticity. The color rendering index for the "daylight" fluorescent is only 75 vs. 100 for natural light and the energy it produces in the near-ultraviolet image is only 37 microwatts/lumen or only about 1/10 that present in natural light. The other sources listed are of a low color temperature, have a poor color rendering index, or have excessively low or high ultraviolet energy content, as compared to natural light.

The present invention is directed to electric lamps which have controlled amounts of ultraviolet energy output in the near and middle ultraviolet energy range and which produce an amount of light output at an acceptable color to be useful as a general illuminant. In accordance with the invention, several types of lamps are described in which the amount of ultraviolet energy in the middle and near ultraviolet ranges is controlled to approximate that of natural daylight. These lamps also have spectral radiation characteristics which produce light having a color closely approximating that of daylight and a relatively high color rendering index.

Accordingly, it is an object of this invention to provide a light source having the characteristics required in a good illuminant and at the same time having a controlled output of middle (290-320 nm.) and near (320-380 nm.) ultraviolet radiation.

Another object of this invention is to provide a general illuminant having a color rendering index over 50 in which there is simultaneously present both middle range ultraviolet (290-320 nm.) and near ultraviolet (320-380 nm.) in a radiant power ratio of near-UV/middle-UV of between 8 and 40.

Another object is to provide a light source of high color rendering index which also emits ultraviolet light in substantially the same proportion per lumen as natural light for the purpose of showing fluorescent objects and colors as they would appear under outdoor light.

It is also an object of this invention to provide a general illuminant which is also a plant growth lamp and which emits ultraviolet radiation in the 290-320 nm. (middle-UV) range of 6-50 microwatts per lumen of visible light emitted and in the 320-380 nm. (near-UV) range of 150-700 microwatts per lumen of visible light emitted and in which the ratio of near-UV/middle-UV lies between 8 and 40.

Other objects and advantages of the present invention will become more apparent upon consideration of the following specification and annexed drawings in which:

FIG. 1 is a perspective view, partially broken away, of a fluorescent lamp made in accordance with the present invention;

FIG. 2 is a graph showing the transmittance characteristics of one type of glass useful in making the lamp of FIG. 1;

FIGS. 3 and 4 are graphs comparing lamps of the present invention with prior art fluorescent lamps; and

FIG. 5 is a view, partially broken away, of a mercury vapor lamp made in accordance with the present invention.

FIG. 1 shows a typical fluorescent lamp constructed in accordance with the present invention which produces an output which closely matches the characteristics of natural daylight in the visible and UV regions. As shown, the lamp 1 is of conventional construction and includes an elongated tubular glass envelope 2 which is sealed at each end, usually by a glass stem 3. A pair of lead-in wires 4, 5, are mounted in and extend through the stems 3, each supporting a filament 6 which may be typically of tungsten. The filaments 6 can be of the double or triple coiled types, or coiled-coil, and they have the usual electron-emissive coating of an alkaline earth oxide. A small amount of zirconium dioxide also may be used in the filaments, as is conventional in the art.

The envelope 2 contains a fill of inert gas such as argon at low pressure, for example, about 2 mm. of mercury. A small quantity of an ionizable material such as mercury is also utilized so that the lamp can be operated at a mercury vapor pressure of between about 2 and 10 microns, for example. A base 7, from which contact prongs 8 and 9 extend is cemented to each end of the envelope. The contact prongs of each base are connected to the lead wires 4 and 5 and the prongs on the two bases, in turn, are adapted to be inserted into the sockets of a fluorescent lamp fixture. All of the features of the lamp heretofore described are conventional and can be varied in a manner well known to those skilled in the art.

To produce the desired spectral characteristics, the fluorescent lamp 1 of the preferred embodiment of the invention utilizes an envelope 2 having a transmittance characteristic suitable to pass a substantial portion of any ultraviolet energy produced having a wavelength above about 290 nm. The transmittance characteristic of one suitable type of glass, which is commercially available from Corning Glass Works of Corning, New York as Code 0080 glass, is shown in FIG. 2. Corning Glass 9821 also may be utilized. As seen, the transmittance increases from zero at about 270 nm. to about 50 percent at 300 nm. and then to substantially the maximum value of 90 percent at about 345 nm. The main requirements of any glass utilized are that it can pass energy above 290 nm. and block any substantial UV energy below the range, which might be harmful.

The inside of the envelope 2 is coated with a phosphor material 10 which produces the light in response to the resonance radiation of the ionized mercury.

Table II below, lists two typical phosphor mixes which can be utilized with the lamps of the subject invention to produce desired spectral radiation characteristics:

TABLE II

Phosphor Composition Used For Fluorescent Lamps

Mix A Mix B Weight % Phosphor 7500.degree.K 96 CRI 5500.degree.K 91 CRI __________________________________________________________________________ Strontium Calcium Orthophosphate:Tin 44.7 68.3 Magnesium Tungstate 20.8 22.2 Calcium Tungstate 13.7 Magnesium Fluorogermanate 6.8 Yttrium Vanadate:Europium 3.3 Barium Silicate:Lead 9.0 5.0 Calcium Zinc Phosphate:Thallium 2.0 Zinc Silicate:Manganese 4.5 __________________________________________________________________________

As indicated in Table II, phosphor Mix A operating in conjunction with the glass envelope of transmittance shown in FIG. 1, produces a lamp having a color temperature of 7500.degree. K and a color rendering index of 96. The spectral distribution of this lamp is shown in FIG. 3 (dotted line 20) compared with natural daylight (Judd reconstituted) at the same color temperature (solid line 22). Wavelength is plotted along the x axis and energy in terms of average microwatts per 10 nm. per lumen along the y axis. The 10 nm. designation refers to the width of the spectrum of energy measured at a given time and integrated. The integrated areas are depicted in block form for the sake of clarity rather than in the more conventional continuous curve form. As seen, the lamp of the subject invention produces a close match to daylight at the same color temperature. It also has a CRI of 96, which is close to that of natural daylight.

Phosphor Mix B, used with the envelope material whose transmittance characteristics are depicted in FIG. 2, produces a lamp having a color temperature of 5500.degree. K and a color rendering index of 91. The spectral characteristics of this lamp are shown in FIG. 4 (solid line 30) as compared to a standard "cool white" lamp (dotted line 32). It should be noted that the lamp of the invention has considerably more energy output in the near UV, violet, blue, green and red ranges and less in the yellow range.

Table III below is a comparison of the spectral characteristics of the lamps produced by phosphor Mixes A and B and the glass with transmittance characteristics of FIG. 2, natural daylight at the same color temperatures and a so-called "cool white" fluorescent lamp.

TABLE III

Microwatts per Lumen

Wavelength 5500.degree.K 5500.degree.K cool 7500.degree.K 7500.degree.K Region 91 CRI natural white 96 natural light CRI light __________________________________________________________________________ Middle-UV (280-320 nm.) 20 10.7 26 26 28 Near-UV (320-380 nm.) 254 255 30 530 535 Violet (380-450 nm.) 543 567 363 610 898 Blue (450-500 nm.) 835 882 554 1144 1128 Green (500-570 nm.) 1077 937 735 1014 993 Yellow (570-590 nm.) 787 704 1070 658 682 Orange (590-610 nm.) 735 743 760 681 671 Red (longer than 610 nm.) 620 824 246 605 681 __________________________________________________________________________

The data for Table III and FIGS. 3 and 4 was computed in the manner described below. A relative spectral power distribution normalized to equal lumens for each light source was plotted on graph paper for each of the light sources. Mercury lines were computed for a 10 nanometer bandwidth and plotted separately. The power distribution curves were separated into the respective bands by drawing vertical lines from the wavelength axis to the continuum thus giving an enclosed area for each band under the curve. The total area under the entire curve and the areas of each separate band where then measured using a compensating polar planimeter. The areas for each band were then divided by the spectral bandwidth in tens of nanometers giving an average height for each band. The absolute value in microwatts per lumen per 10 nanometers for the near-uv band was then determined as follows:

where:

J.lambda. = average radiant flux in microwatts per lumen per 10 nm.

A.sub.uv = area of near-uv band

A.sub.s = total area under spectrum

685 lumens/watt = electrical equivalent of light at 555 nm.

L = luminosity factor = .SIGMA. J.lambda.y/.SIGMA. J.lambda.

j.lambda. = relative spectral power at wavelength .lambda..

Y = CIE 1931 Standard Observer Function.

Values of microwatts per lumen per 10 nm. for the remaining bands were then computed using the ratio J.lambda..sub.uv /A.sub.uv as a constant to convert the area measurements into the absolute values.

As seen in Table III the 7500.degree. K, 96 CRI lamp provides a relatively good match of the spectral radiation characteristics of natural daylight at the same color temperature. The same holds true for the 5500.degree. K, 91 CRI lamp.

Both the aforesaid lamps of the present invention also are suitable as general illuminants. For example, both of these lamps constructed in a 40 watt size produce approximately 2100-2300 lumens of light output as measured in a conventional manner. This compares quite favorably with the more conventional fluorescent lamps whose light output, for the same size lamp, is approximately the same for so-called "deluxe" fluorescent lamps.

It should be understood that the phosphor Mixes A and B referred to above are only typical of a number of phosphor mixes which can be utilized. In the Mixes A and B, Barium Silicate:Lead produces energy in the near-UV range and Calcium Zinc Phosphate: Thalium in the middle UV range. In general, the necessary quantities of these two phosphors are selected to produce the desired UV radiation output and then the other phosphors blended to produce the proper color and CRI. It should be understood that, in general, the proportions of the phosphor mixes of the type described above using the same constituents will vary due to changes in the relative efficiencies of the different phosphors.

The principles of the present invention are not limited to low pressure fluorescent lamp types and other types of lamps can be produced having a controlled amount of ultraviolet energy and still be useful for general illuminant purposes. For example, by using a subtractive filter to selectively reduce the ultraviolet radiation from a high pressure mercury lamp (e.g., type H33-1CD as specified by the American Standards Institute) the ultraviolet output per lumen may be brought within the ranges found in natural light. This can be achieved in one embodiment of this invention by adjusting the coating thickness of an ultraviolet absorber such as manganese activated magnesium fluorogermanate phosphor so as to transmit only about 15 percent of the middle- and only about 30 percent of the near-UV radiation. Heretofore this phosphor has been utilized (see U.S. Pat. No. 2,748,303) for color improvement of this lamp type in which case it is important that all ultraviolet be absorbed in order to have the highest conversion of this radiation into red luminescence. This contrasts with the present invention where it is important to allow a controlled amount of the middle- and near-UV to be radiated by the lamp so as to more closely match natural light. By proper adjustment of this coating, it has thus been found possible to achieve ultraviolet emission levels in this type lamp of about 16 microwatts and 280 microwatts per lumen respectively for the middle- and near-UV regions per lumen of visible light emitted. This brings the lamp quite close to the UV ratios found in natural light although the spectral distribution in the visible range is not quite as good as that produced with the fluorescent lamps described previously. The lumen output of such mercury vapor lamps modified as described above is about 50 lumens per watt.

FIG. 5 shows a mercury vapor lamp constructed in accordance with the present invention. Here, the otherwise conventional lamp has an envelope 40 with a screw type base 42 in which is mounted an arc tube 44 on a support 47. Lead wires 46 and 48 connect the electrodes 50 and 52 of the arc tube to the electrical contacts of the base. The arc tube contains a quantity of mercury which is ionized to produce the light. The interior wall of envelope 40 is coated with the UV absorbing phosphor 49 compound previously described. It should be understood that the thickness of the phosphor coating depends upon the phosphor particle size. Thus, finer phosphor particles can be more densely packed and a thinner coating used to produce the desired amount of absorption, than if larger size phosphor particles are utilized.

Lamps such as high pressure sodium and metal-halide-mercury sources also are correctable by means of either UV emitting phosphors on the outer envelopes and/or additions of other vapor species to the arc itself so as to radiate proportions of ultraviolet energy in the ranges required to simulate what is found in natural light. While such lamps with controlled UV/visible ratios of radiated energy are within the scope of the present invention, they do not represent the best illuminants by reason of their inferior color rendering indexes and discontinuous spectra.

As indicated above, the lamps of the subject invention produce ultraviolet energy in the middle and near ultraviolet ranges in quantities per lumen comparable to natural daylight while at the same time producing sufficient light output at an acceptable color to serve as a general purpose illuminant, e.g., as a light source where prior art fluorescent lamps are utilized such as in factories, schools, homes, offices, etc.

In accordance with the preferred embodiment of the invention, the glass transmittance characteristics, such as types of glass compositions and thickness and/or the phosphor mixes, and other factors, are selected to produce a lamp: having a CRI of about 50 or greater; an output of middle UV energy in the range of 6-50 microwatts per lumen of visible light emitted; an output of near UV energy in the range of 150-700 microwatts per lumen of visible light emitted; and in which the ratio of near UV/middle UV energy emitted is in the range between about 8 to 40.

The ranges of operation of the various output parameters specified above are selected for the following reasons. First, a CRI of at least 50 is preferable, for a lamp used as a general illuminant since CRIs below this value have very poor color rendering and therefore are poor from the standpoint of perception. Outputs of 6-50 microwatts of middle range UV and 150-700 microwatts of near range UV energy per lumen of visible light emitted by the lamp and maintenance of the ratio of near UV/middle UV in the range of from about 8 to 40 is also desired. The reason for this is that this range of energy outputs and ratios approximates the range of the standard color temperature of natural daylight from about 5000.degree. K to about 8000.degree. K which is suitable for illumination purposes. Too far a departure from these temperatures would bring a lamp in the range to where its light output would have a color unsuitable for general illumination purposes. As should be apparent the color temperature of natural daylight varies due to various external factors, including the seasons of the year, and therefore it is impossible to fix upon any one color temperature.

It is also desirable to limit the UV energy output to the ranges specified above in order to prevent undue erythema (burning or reddening of the skin) upon exposure to the lamp. It is preferred that a person exposed to the lamp over a given period of time, say an eight hour day, receive less than one MPE (minimum perceptible erythema), which is the quantity of UV energy needed to produce just noticeable reddening of the average untanned skin of a caucasian human. Using the 5500.degree. K, 91 CRI fluorescent lamp described above, a person exposed to a 100 footcandle level from this lamp (the average level found in an office) over an eight hour day would receive approximately one-third of an MPE.

To produce a lamp such as shown in FIG. 1 is a relatively simple matter. Starting with a glass which can transmit UV energy above 280 nm. the phosphors emitting UV energy, such as in Mixes A and B above, are first chosen in the quantity desired to produce the needed amount of UV energy. Then the color emitting phosphors are selected to produce the desired CRI. Adjustments of both can then be made, if needed, to achieve both the desired quantity of UV energy and proper CRI.

In the past certain special lamps have been developed for producing certain types of energy for the purpose of of promoting specific biological effects. For example, the fluorescent lamp described in U.S. Pat. No. 3,287,586 is said to have been developed to improve the growth of specific plants such as green beans and tomatoes. The color (x = 0.392, y = 0.331) of this lamp departs considerably from acceptable white sources so that the CIE Color Rendering Index is very low or cannot logically be applied at all. Also, the lumen output of visible light of a lamp of this type is quite low as compared to conventional fluorescent lamp sources used for general illumination purposes.

Similarly, fluorescent lamps have been developed for the specific purpose of producing ultraviolet for sun tanning purposes. However, these fluorescent lamps have no utility as general illuminants whatsoever.sup.1. Other lamp types, such as the "RS Sunlamp", have been designed as sources of ultraviolet energy. These "sunlamps" are advertised as having health benefits in synthesizing Vitamin D and aiding the growth of strong healthy bones and teeth. While these "sunlamps" do have visible radiation, their color temperature (see Table I) is so far from the black body locus as to prohibit assignment of a meaningful color rendering index. Further, their luminous efficacy (in the order of 9 lumens/watt) is so low as to render them very poor choices as general illuminants. They also could not be used for general illumination purposes even if it were desired to do so because of the inherent danger to people of the high ultraviolet intensities which accompany the visible light. For example, to achieve an illumination level of 50 foot-candles with such a source, a person receiving this amount of light would be exposed to about 30 microwatts/cm.sup.2 of middle ultraviolet energy in the range between 290 and 320 nanometers which produces erythema. The maximum intensity tolerated by the American Medical Association at face level for an 8-hour day is 0.5 microwatts/cm.sup.2..sup.2 This maximum intensity level was actually specified for bactericidal UV (253.7 nanometers) but was based on experience with wave-lengths in the 280-320 nm. range..sup.3

In addition to serving as a general illuminant, it is believed that the lamps of the present invention have advantageous photobiological effects. For example, particularly good results have been obtained with fluorescent lamps of the first example (5500.degree. K and CRI of 91) in plant growth and seed germination. The flower varieties of ageratum begonia, impatiens, Iobelia, petunia, salvia, verbena, and vinca rosea were found to germinate and grow particularly well. Seeds of these varieties started two weeks after the normal sowing date, caught up to the stage at which the same species were a year earlier at the same time under energy from the lamps of U.S. Pat. No. 3,287,586. Early germination and rapid early growth were also found for kidney beans and dwarf marigolds under the fluorescent lamps of 5500.degree. K and CRI of 91 of the present invention, and after 66 days, healthy mature fruited and blossomed plants were obtained.

Considerable research work is presently being done on other aspects of the photobiological effect of light. The lamps of the present invention also produce energy in ranges where it has been shown that other advantageous photobiological effects are produced. To demonstrate these possibilities, the charts of FIGS. 3 and 4, which show the spectral output of typical lamps of the present invention, have been divided spectrally into known photobiologically active regions from the shorter wavelength (middle) ultraviolet, to the longer wavelength radiations between 625 and 700 nm. Radiation from natural daylight in the former, shorter wavelength region has been shown to form Vitamin D in the body. Energy from natural daylight in the latter, longer wavelength region, which evokes the sensation of red light in the human eye, has been shown to have pronounced photoblastic effects upon seeds. Such photobiological effects related to the various bands are shown in Table IV together with pertinent literature references.

Since the different wavelengths of light found in natural daylight and considered in the literature references of Table IV are present in the lamps of the subject invention, it is believed that a number of the same beneficial effects of natural daylight can be obtained with these lamps. For example, it is believed that the lamp of 7500.degree. K color temperature and CRI of 96 has bactericidal effectiveness in a manner comparable to that of natural light. As described in one literature reference, 10, natural daylight provides a lethal environment for such organisms as streptococci even at ##SPC2## levels as low as 40-50 footcandles. This reference describes that inactivation of certain bacteria (E. coli) by sunlight is even more effective than ultraviolet alone (253.7 nm.) in that the sunlight inactivated cells are least susceptible to reactivation processes. Since the 7500.degree. K, CRI 96 lamp spectral distribution closely matches that of natural light, it should have a similar effectiveness. Thus, it would be a good illuminant for use in general hospital illumination.

All of the above described lamps of this invention (both fluorescent and vapor types) will supply ultraviolet energy at reasonable footcandle levels which has shown in the literature to be sufficient to cure and/or prevent rickets in humans and growing chicks..sup.7

In recent years considerable research work has been done which leads to the conclusion that natural light is the most important environmental factor controlling and molding life on earth..sup.19 This has been universally understood for a long time in the case of plant life where light directly powers the remarkable process of photosynthesis. Here carbon dioxide and water are converted into the basic building blocks of all life. As might be expected, the intensity, periodicity, and spectral composition of light used for growing plants can have drastic effects upon them. However direct effects of light upon mankind and animal life have not been so obvious. Only now is the complexity of the interrelations between light and these forms of life beginning to unfold.

Research conducted at the National Institutes of Health in the last several years has revealed that a small gland near the center of the brain responds to light entering the eye. This response is independent of and apart from the normal visual process. Under stimulation of light entering the eye, this gland, called the pineal gland, controls the synthesis and release of chemical substances (hormones, enzymes) into the bloodstream to be carried to any one of several target sites in the neuroendocrine system including the brain, the pituitary, and the gonads..sup.16 Earlier work had already indicated retinal stimulation of the hypothalamus-pituitary system which regulates vital autonomic function of the body. Before this discovery, there had been numerous observations of biological effects of light and its spectral composition on people and animals although the exact processes were not understood. These go back over 40 years when it was discovered.sup.20 that slate-colored junco could be made to migrate north in the fall by simply varying the light-dark cycle to which they were exposed before release.

Subsequent reports of photobiological effects have ranged from those involving regulation of the water, carbohydrate, blood, and hormone (including insulin and ACTH).sup.17, 21, 22 balance in humans to those involving grotesque effects upon animals of spectrally distorted light sources. The latter include such effects as abnormal gonadal development.sup.17 and cancer.sup.23, 24. Studies of blind people as compared with seeing people have shown remarkable differences in age of sexual maturity.sup.25 and in the size of the pituitary gland..sup.17

Light also has direct beneficial effects upon the human body when absorbed through the skin. These are well known effects such as the formation in the body of vitamins by ultraviolet and improved lime, phosphorus, and carbohydrate metabolism..sup.4 Then there is the greatly sought after cosmetic effect of skin tanning long associated with a healthy condition of the body. These are extremely complex reactions affected drastically by the balance of ultraviolet between the shorter wavelengths (middle UV) and the longer wavelengths (near UV and visible). For example the short wavelengths alone can cause a burning (erythema) of the skin while the longer wavelengths alone cause a direct pigment darkening without burning..sup.5 Only with simultaneous exposure to both types of light in proper balance does one get the natural skin responses. Remarkably it has been found only recently that the oral administration of Vitamin D could not replace the effects of ultraviolet absorbed by the skin in forming the same vitamin..sup.6

Effects of light on bacteria are also complex. Shorter wavelengths of ultraviolet alone inactivate them while longer wavelengths seem to repair the damage to certain types. Simultaneous irradiation with all wavelengths as present in sunlight therefore has a very complex effect..sup.11 Viruses alone on the other hand show no repair effects under longer wavelengths -- they are inactivated by ultraviolet alone or in combination with longer wavelengths.sup.8 unless they are incorporated within a host cell showing photo-repair characteristics. Recent studies on full spectrum natural sunlight have demonstrated its effectiveness against both viruses and bacteria..sup.9, 10

The action spectra for bacterial inactivation and erythemal effectiveness have been determined of necessity by isolating the various UV wavelengths and measuring their biological effectiveness. They are not realistic for sources in which longer wavelengths of ultraviolet-and visible-radiation are simultaneously present. There results a more complex interplay of biological effects in full spectrum radiation such as found in natural light than is observed for monochromatic or narrow band sources. Such phenomena extend to the visual process which itself is photo-biological in nature. For example, it has recently been reported that the visual pigment rhodopsin- known to photodecompose upon absorption of light giving rise to rod stimulation is actually photoregenerated by the action of near-UV and violet wavelengths upon the intermediates formed during the bleaching process..sup.15 This has its analogue in the plant world where photoblastism, that is, the influence of light upon seed germination shows remarkable reversible effects. Germination of certain seeds is inhibited by one wavelength (730 nm.) and stimulated by another (660 nm.). Simultaneous irradiation by both wavelengths with white light gives results dependent upon which wavelength is preponderant. Such complex photobiological effects are closely attuned to natural light. Another researcher.sup.26 has concluded that "I have no doubt that adaptation to sunlight is one of the principal circumstances that govern the action spectra of photo-biological processes."

It has also been recently discovered that small quantities of ultraviolet light bring about profound changes in living cells. Thus, while ultraviolet may bring about in living skin the formation of a small amount of melanin according to reactions such as have been demonstrated in vitro, the skin might be pretty thoroughly burned before the quantity reaches the proportion of suntan. On the other hand, a very small amount of ultraviolet radiation might, by eliciting changes in the cell, lead to the ultimate production of a good deal of melanin..sup.27 Melanin is the pigment responsible for skin darkening. The foregoing relates to actual synthesis of melanin in the malphigian layer of the skin due to middle-UV exposure. Near-UV as mentioned earlier has the property of eliciting direct pigment darkening due presumably to oxidation of existing melanin in the outer layers of skin.

As on other important aspect of photobiological effects, it should be considered that up to now, scientists thought the body's biological clock mechanisms operate independently of external influences. Now the discovery of the pineal's direct neural connection with the eyes and the influence of light on synthesis of hormones exposes the error of the theory..sup.28

It is also known that quantities of UV energy have been successfully used to promote the general health of humans and animals.

As can be reasonably concluded from the above, it is believed that the lamps of the present invention, whose spectral radiation characteristics closely match natural daylight, could have significant utility in producing various beneficial photo-biological effects. This is so because the lamps produce a full spectrum of energy containing energy in the specific range, or ranges, which have been shown in the literature to produce some photobiological activity. The plant growth tests already conducted with the lamps of the present invention, have already substantiated a portion of this conclusion.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims.

APPENDIX

1. wollentin, et al, Journal of the Electrochemical Society, 97(1), p. 29 (1950).

2. Jo. of American Medical Assoc. 137, 1600-1603.

3. Radiation Biology, Vol. II, p. 53, McGraw-Hill (1955) Ed. by Alexander Hollaender.

4. IES Lighting Handbook, fourth Edition, p. 25-14 (1966).

4a. ibid p. 25-12.

5. Blum, H. F., ref. No. 23, p. 487.

6. Seidl, E., "Influence of Ultraviolet Radiation on the Healthy Adult", Max-Planck-Institut fur Arbeitsphysiologie (paper presented at Conference on Biologic Effects of Ultraviolet Radiation held at Temple University Sciences Center, Aug. 1966).

7. Luckiesh, Matthew, "Applications of Germicidal Erythemal, and Infrared Energy," Van Nostrand (1946) p. 135-136.

8. Luria, S. E., ibid, p. 333.

9. Harm, Walter, Radiation Research Supplement 6, p. 215 Academic Press (1966).

10. Buchbinder, L. et al, J. Bacteriology, Vol. 42, 1941, p. 353-366.

10a. IES Handbook, fourth Edition, FIG. 25-23.

11. dulbecco, Renato, ref. No. 23, p. 455.

11a. Rupert, Claud S., Photophysiology, p. 283, Academic Press (1964) Ed. by A. C. Giese.

12. Rushton, W. A. H., ref. 13a., p. 126

13. Clare, N. T., Radiation Biology Vol. III, p. 693, McGraw-Hill (1956).

14. Blum, H. F., Photo-Dynamic Action & Diseases caused by Light, Hafner Pub. Co. (1964).

15. Pak, W. L. and Boes, R J., Science, Vol. 155(3766), p. 1131 (1967)

16. Wurtman, R. J. and Axelrod, J., Scientific American 213(1), July 1965.

17. Hollwich, F., Annals of The New York Academy of Sciences 117, p. 105-127.

18. Benoit, J., ref. 17, p. 204.

19. Evenari, M., Recent Progress in Photobiology, p. 161, Blackwell Scientific Publications (1965).

20. Rowan, William, Nature 155:p. 494-495 (1925).

21. Jones, E., Deut. Arch. Klin. Med. 175:244 (1933).

22. Radnot, M. and Wallner, E., ibid p. 244-253.

23. Blum, H. F., Radiation Biology Vol. II, p. 529, McGraw-Hill Book Co. (1955).

24. Ott, John N., Illuminating Engineering, Vol. LX, p. 254 (1965).

25. Wurtman, R. J. and Zacharias, L., Science Vol. 144(3622), p. 1154.

26. Wald, George, Ref. No. 1, p. 336.

27. Harold F. Blum, ref. 23, p. 507.

28. Chemical & Engineering News, May 1, 1967, page 40.

Claims

What is claimed is:

1. An electric lamp for general illumination purposes operable from a source of voltage comprising an envelope capable of transmitting light in the visible, and middle and near ultraviolet ranges, a pair of electrodes for connection to said voltage source and an ionizable medium within said envelope, said electrodes and said ionizable medium upon operation of the lamp producing an electrical discharge, means cooperating with the radiant power of the electrical discharge for producing radiation having a spectrum in the visible light range with a C.I.E. color rendering index of at least 80, radiation in the near ultraviolet range, and radiation in the middle ultraviolet range, said visible and said ultraviolet radiation produced being transmitted through said envelope in the quantities of between about 6-50 microwatts of middle range ultraviolet radiation and between about 150-700 microwatts of near range ultraviolet radiation per lumen of visible light with the radiant power ratio of near ultraviolet/middle ultraviolet radiation being in the range from between about 8 to 40, said ultraviolet radiation transmitted through said envelope being of a total quantity substantially the same per lumen of visible light transmitted through said envelope as found in natural daylight of the same correlated color temperature.

2. An electric lamp as in claim 1 wherein said means cooperating with the radiant power of the electrical discharge produces respective quantities of radiation transmitted through said envelope in each of said middle and near ultraviolet ranges per lumen of visible light which are substantially the same as that found in the corresponding ranges of natural daylight for the same correlated color temperature.

3. An electric lamp as in claim 1 wherein said means cooperating with the radiant power of the electrical discharge produces ultraviolet radiation transmitted through said envelope in the middle ultraviolet range which is of a quantity less than that which would produce minimum perceptible erythema on an average untanned caucasian skin during exposure for an eight-hour period at a 100 foot candle level.

4. An electric lamp as in claim 1 wherein said envelope is of a material which substantially blocks the transmission of radiation below 290 nanometers.

5. A fluorescent lamp for general illumination purposes operable from a source of voltage comprising an ultraviolet and visible light transmitting envelope, a pair of electrodes for connection to said voltage source, an inert gas and an ionizable medium within said envelope for producing an electrical discharge upon operation of the lamp, means including a blend of phosphors internally coated on said envelope for producing upon operation of the lamp and in cooperation with the radiant power of the electrical discharge radiation which is transmitted through said envelope including visible light having a C.I.E. color rendering index of at least 80, and an ultraviolet emission of radiation in both the near and the middle ultraviolet ranges which is transmitted through said envelope in the quantities of between about 6-50 microwatts of middle range ultraviolet radiation and between about 150-700 microwatts of near range ultraviolet radiation per lumen of visible light with the radiant power ratio of near ultraviolet/middle ultraviolet radiation being in the range from between about 8 to 40 and the quantity of total ultraviolet radiation being substantially the same per lumen of visible light transmitted through the envelope as found in natural daylight of the same correlated color temperature.

6. A fluorescent lamp as in claim 5 wherein said means including the blend of phosphors which cooperates with the electrical discharge produces respective quantities of radiation transmitted through said envelope in each of said middle and near ultraviolet ranges which are substantially the same as that found in the corresponding ranges of natural daylight for the same correlated color temperature.

7. A fluorescent lamp as set forth in claim 5 wherein the envelope is of a material which limits the transmittance of the short wavelengths of ultraviolet radiation produced substantially to above 290 nanometers.

8. A fluorescent lamp as set forth in claim 5 wherein the phosphor blend comprises at least the following phosphors:

Strontium Calcium Orthophosphate:Tin

Magnesium Tungstate

Barium Silicate:Lead

Zinc Silicate:Manganese.

9. A fluorescent lamp as set forth in claim 8 wherein the phosphor blend comprises at least the following phosphors at substantially the weight percentages of the total blend indicated:

to produce a lamp having a color rendering index of visible light of about 91 at about 5500.degree. K color temperature.

10. A fluorescent lamp as set forth in claim 5 wherein the phosphor blend comprises at least the following phosphors:

Strontium Calcium Orthophosphate:Tin

Magnesium Tungstate

Calcium Tungstate

Magnesium Fluorogermanate

Yttrium Vanadate:Europium

Barium Silicate:Lead

Calcium Zinc Phosphate:Thallium

11. A fluorescent lamp as set forth in claim 8 wherein the phosphor blend comprises at least the following phosphors at substantially the weight percentages of the total blend indicated:

to produce a lamp having a color rendering index of visible light of about 96 at about 7500.degree. K color temperature.

12. A fluorescent lamp as in claim 5 wherein the visible light produced has a color temperature of between about 5000.degree. K and about 8000.degree. K.

13. A fluorescent lamp as in claim 5 wherein said means including said blend of phosphors for cooperating with said electrical discharge produces light in the visible range with a ratio of the yellow to red components thereof being substantially less than 10:1 at about 5500.degree. K color temperature.

14. A fluorescent lamp as in claim 5 wherein said means including said blend of phosphors for cooperating with said electrical discharge produces light in the visible range with a ratio of the yellow to red components thereof being substantially less than 7:1 at about 7500.degree. K color temperature.

15. The fluorescent lamp as in claim 5 wherein said means including said blend of phosphors which cooperates with the electrical discharge produces substantially no infra-red radiation.

16. A fluorescent lamp as in claim 5 wherein the phosphor blend is substantially uniformly distributed on the internal surface of the envelope.

17. A fluorescent lamp as in claim 5 wherein said means including said blend of phosphors which cooperates with the electrical discharge produces light having a C.I.E. color rendering index of at least 85.