30 March 1973, Volume 179, Number 4080

Light PollutionOutdoor lighting is a growing threat to astronomy.

Kurt W. Riegel

It is my purpose in this article todelineate astronomical dark sky re-quirements for scientifically useful ob-serving, to survey the influence onastronomical observing conditions ofman-produced electromagnetic radia-tion, to examine what conditions willprobably prevail for the next generationor two of observing astronomers, andto suggest changes in public policy thatwould alleviate some of the actual andprojected damage to the astronomicalobserving environment. During thiscentury, astronomers have had to con-tend with the phenomenon of light pol-lution, defined here as unwanted skylight produced by man, because of pop-ulation growth and increased outdoorillumination per capita. Both of thesecauses of increased light pollution areimportant, the former having beenmore important early in the centuryand the latter being of most concernnow.

Survey of the Problem

The last hundred years have beenmarked by two periods of very rapidgrowth in astronomical observing facili-ties in the United States. Both wereinitiated by the dual factors of im-proved techniques and favorable fund-ing conditions. The early period, for

The author is assistant professor of astronomyat the University of California, Los Angeles 90024.His present address is Sterrewacht, Leiden, TheNetherlands.

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spectrum as possible, since the quantummechanical correspondence betweenwavelength and energy implies thatphysical processes of radically differentintrinsic energies produce radiation atwidely differing wavelengths. The com-plete astronomical picture can comeonly from observations gathered at allwavelengths.The transmission properties of the

earth's atmosphere severely restrict theportions of the spectrum available forground-based astronomical measure-ments. Figure 1 shows the atmospherictransmissivity as a function of wave-length. The electromagnetic spectrum isdivided into a number of segmentscalled windows, where the transmissiv-ity is near unity. The optical windowis the one which has received the mostastronomical attention, for the naturalreasons that our eyes respond at thesevisual wavelengths and that solar-typestars emit the bulk of their radiation atthese wavelengths. The sun is a com-mon sort of star in this respect, al-though there are many astronomicalobjects that emit most of their light atwavelengths outside the optical window.

Over much of the spectrum one mustobserve from above the earth's atmo-sphere because of its very high opacity;orbiting astronomical observatories con-tribute to our knowledge of astrophysicsat infrared, ultraviolet, x-ray, andgamma-ray wavelengths. They have theadvantage of immunity from scatteredatmospheric light since they are in thenear vacuum of space. The cost ofdoing astronomy from above the earth'satmosphere is high, although intelli-gently planned programs of this typeare well worth the expense. Where onehas the choice of making astronomicalmeasurements from space or usingground-based facilities, one would al-ways prefer the latter on economicgrounds, all other things being equal.Thus, there is some economic justifica-tion for preserving our ability to con-tinue to make useful astronomical mea-surements from the ground. Moreover,many types of observations, such asthose involving untried experimentalequipment and techniques, or particu-larly bulky apparatus, cannot be done

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example, saw the development of pho-tography and spectroscopy when therewas something of a fad for privatephilanthropy to observatories. Techno-logical improvements made much moresensitive and accurate measurementspossible at a time when appreciationfor the scientific value of astronomicalobservations was growing. Wealthybenefactors provided the necessaryfunds to construct such observatoriesas Leander McCormick (Charlottes-ville, Virginia), Lick (San Jose, Cali-fornia), Yerkes (Williams Bay, Wiscon-sin), Mount Wilson (Pasadena, Cali-fornia), and McDonald (Fort Davis,Texas). These observatories werefounded at a time when cities weresmafl and dimly lit by today's standards.

During the second period, improve-ments in technology provided some im-petus for the construction of new opti-cal observatories in Hawaii, Arizona,Texas, and Chile. Again, a dramatic in-crease in available funds was a decisivefactor, only now they were mainly pub-lic funds and related to the nationalspace program. The latter period of ex-pansion of astronomical facilities wasaccompanied by rapid expansion of ourcities and populated suburban areas,and by technological improvements inoutdoor lighting.

It is the goal of the astronomer todeduce as much as he can about thenature of various cosmic sources ofelectromagnetic radiation. He wouldlike to extend his observations to in-clude as much of the electromagnetic

log A(nm)

Fig. 1. Transparency of the earth's atmosphere as a function of wavelength (X). Theoptical window lies at the extreme left and the radio window at the extreme right.

in orbit. Light pollution renders ground-based observations more and more dif-ficult to perform.

Basically two types of measurements,narrow band and broad band, are madeby astronomers, Examples are high-resolution spectroscopy of stars andphotography of very distant objects likegalaxies and quasars, respectively. Thesources of interference are of the same

two types. If the interference is narrow

band, then most of the spectrum re-

mains free from interference. On theother hand, within the narrow rangeof wavelengths affected by the interfer-ence, the problem will be very seriousfor a particular power level. If theinterference is broad band or consistsof a large number of spectral lines thenthe astronomer cannot escape it. How-ever, for a particular interference powerthe intensity at a particular wavelengthwill be less, since the radiation is dis-persed throughout a wide range ofwavelengths. We may find that in spiteof some broad-band (continuum) inter-ference, narrow-band observations ofbright cosmic sources are still possible.Moonlight is an example of a source oflow-level continuum interference affect-ing optical measurements at certaintimes of the month-astronomers rou-

tinely do high-resolution spectroscopyof bright stars under such conditions.Narrow-band observations are still pos-

sible even with relatively intense inter-ference, if that interference is confinedto wavelengths outside the spectral re-

Visual sensiti,

Fig. 2. Wavelengthresponse of the hu-man eye and spec-trum of a blackbodyat the temperatureof a typical incan-descent lamp. Mostof the radiation pro-duced by incandes-cent lamps evokesno visual response;hence, they have lowluminous efficiency.

gion of interest. As an example, low-pressure mercury vapor lamps producerelatively few but intense spectral lines,with large gaps between them; as longas one is concerned only with detailsin the spectrum between the interferinglines, there is no serious problem. Un-fortunately, this is often not the case;

for example, the spectral line for triplyionized oxygen (O III) at 436.3nanometers, which is critical in theplasma diagnostics of gaseous nebulas,is near the 435.8-nm mercury line.

Broad-band measurements such as

astronomical photography and photo-electric photometry are seriously af-fected by interference, whether it is inspectral lines or spread over a con-

tinuum, as long as it falls within thepassband being observed. Broad-bandobservations are extremely useful. Sur-veys of areas to faint limiting magni-tude amount to what we might call"astronomical fishing trips," or observa-tions which are intended to aid in thediscovery of new and unsuspectedphenomena. The list of fundamentallyimportant constituents of the universediscovered in this way is impressivelylong.

Astronomical and Scientific Constraints

The astronomer must be able to de-tect the source of radiation he is inter-ested in measuring. His detector willalways indicate some response, even

A(nm)

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when it is not directed at the source ofinterest, because of natural causes in-cluding airglow, atmospheric scatteredlight, ground reflections, zodiacal light,and the light from background stars. Inspite of interference from these causes,from noise generated within the de-tector, and from light pollution, it isstill possible to do useful work, pro-vided that the interference is not toostrong. A high-resolution spectrum ofthe night sky at Kitt Peak NationalObservatory has been published (1).In the visible, for example, the zenithbrightness is of the order 20 x 10-Istilb (2), equivalent to about one starof magnitude 22 per square arc second.This value of the natural sky brightnessprovides us with a standard againstwhich we can measure the consequencesof contaminating the astronomical ob-serving environment with man-madeskylight. As long as the component ofthe local sky brightness which is gen-erated by man is small compared to thenatural level, then light pollution is nota serious matter.

It should be emphasized that thesky brightness sets very real limits forastronomers. Studies of the processesthat produce the light of the night skyform an area of serious research, andthey require dark-sky observing sites.Observations of the zodiacal light, thegegenschein, the airglow, and the aurorarepresent such studies. Observationalcosmology is based on limiting magni-tude results on the faintest quasars andgalaxies, so an increase in sky bright-ness has the effect of shrinking the visi-ble universe. For example, at PalomarObservatory on the 200-inch (5.08-meter) telescope, photographic expo-sures cannot be made for periods oftime longer than that required to justrecord 24th magnitude stars on sensitivephotographic emulsions under the bestobserving conditions. This is becauseof skylight, which fogs photographicplates when exposure times exceed acertain value. As a practical matter, in-creasing the telescope size is an expen-sive and relatively ineffective way tocompensate for skylight, beyond the"seeing" limit, which corresponds toimage blurring due to atmospheric tur-bulence and distortion. The limitingmagnitude depends on the propertiesof the detector (3).The natural sky brightness of about

22 magnitudes within a circle whosediameter is 1 arc second is 2 magni-tudes brighter than the limiting magni-tude given above. This is no coinci-dence, because 1 arc second is the size

SCIENCE, VOL. 179

of a stellar image under good observingconditions, and the photographic limitis reached when the star brightnessdrops below some fraction of the skybrightness. The relation between thesky brightness, B, and the apparentmagnitude, m, of a star which con-tributes light equal to the skylightwithin the seeing circle diameter, S, is

B = 14.35S-210-4'U 20 X 10-9

where the units of B are stilbs when Sis in arc seconds. Thus, the limit set byskylight on the magnitude of the faint-est object that can be photographeddepends also on turbulence in the atmo-sphere, in the sense that bad seeingdecreases the effective sensitivity. Thecorresponding limiting magnitudes areseveral magnitudes fainter, dependingon the f-ratio of the telescope and onthe detector system employed. It is pos-sible to do even better, in principle, byusing techniques of photoelectric pho-tometry and multiple exposure photog-raphy to give longer integration timesand improved signal-to-noise ratios.These techniques are only now comingof age in optical astronomy, but theyare not likely to solve the basic prob-lem of interference due to light pollu-tion because they are applied with dif-ficulty and at great expense.

Outdoor Lighting in the United States

Most outdoor lighting was of theincandescent type until very recently.The filaments of incandescent lights,which operate at only about 2700°K,radiate mostly longward of 550 nm, thepeak of the visual response curve. Thus,incandescent lights have a very lowluminous efficiency, only about 20 lu-mens per watt or less. Figure 2 showsthe visual sensitivity curve for humansand the spectrum of a typical incan-descent lamp. Most astronomical pho-tographic emulsions and photoelectricdetectors have their peak sensitivity to-ward the blue end of the spectrum.Thus, these lamps have two propertieswhich make them desirable to astron-omers: (i) they radiate with very lowefficiency, producing relatively littlelight at visible wavelengths, and (ii)very little of the visible light that isproduced interferes with blue-sensitivedetectors. The first of these propertiesmakes them undesirable to municipallighting departments.The high-intensity gas discharge lamp

is succeeding the incandescent lamp formost outdoor lighting. The mercury30 MARCH 1973

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1950

Fig. 3. Number ratio of in-service mercuryvapor lamps to incandescent outdoor lampsin the United States for the past 22 years.

vapor lamp is the most popular. Suchlamps usually emit most of their lightin a few spectral lines, which is goodfrom the astronomer's point of view.The lighting engineer and the used carsalesman consider this a disadvantage,however, since the appearance of ob-jects tends to be more pleasing in lightwhich has a smooth spectrum moreclosely approximating that of sunlight,perhaps somewhat reddened. In thenewest vapor lamps the continuum por-tion is enhanced and the luminous effi-ciency is as high as 1 15 lumens perwatt, a very significant change in con-nection with light pollution.

Most of the discussion on specificproperties of light sources will refer tohigh-intensity vapor lamps and not theolder incandescents. The relative impor-tance of the incandescent lamp hasbeen rapidly declining, as can be seenin Fig. 3, which shows the relative

600

White mercury

E

E

0

s. Lucalox400

400 600A(nm)

Fig. 4. Spectra of a commonly used mer-cury vapor lamp and the newer high-pres-sure sodium (Lucalox) type of lamp.These are low-resolution spectra, with datapoints only every 10 nm.

numbers of in-service vapor and incan-descent lamps as a function of time(4). This conclusion is also supportedby data from (5), which show that therate of production of outdoor incan-descent bulbs is now virtually constant,reflecting replacement use only; the rateof production of incandescent lumi-naires has declined drastically as thatof high-intensity mercury luminaireshas soared.The growth curve in Fig. 3 can be

used together with power consumptiondata from the same source (4) toderive the 1970 mix of lumens due toin-service vapor lamps and incandescentlamps, respectively. This ratio wasabout 6 in 1970, if it is assumed thatthe vapor/ incandescent number ratiowas 1.16 and the vapor/ incandescentlumen ratio was 5 for typical streetlamps. So, as early as 1970, the bulkof the total luminous radiation in theUnited States, about 85 percent, wasproduced by vapor lamps. However,most of the continuum was still pro-duced by incandescents, since almostall of the mercury light occurs at wave-lengths of 365.0, 404.7, 435.8, 546.1,and 578 nm. The 435.8-nm line hasbeen most annoying to astronomers,since it is by far the strongest; it liesin the blue; and, most frustratingly, itis on the tail of the standard visualresponse curve (Fig. 2), where it con-tributes inefficiently to the lumen outputof the lamp.The spectrum of a commonly used

mercury lamp is presented in Fig. 4.An increasingly popular new type oflamp is the General Electric Lucaloxhigh-pressure sodium lamp, which hasa very high luminous efficiency of 115lumens per watt, or about six times thatof ordinary incandescents. The Lucaloxspectrum also appears in Fig. 4. Itsmost interesting characteristic is strongcontinuum radiation and a much richerline spectrum relative to the cleanermercury vapor lamp spectrum. One hasonly to look at the light from theselamps through a hand-held spectroscopeto see dozens of spectral lines. Thesehigh-pressure sodium lamps do not ac-count for a very high percentage ofoutdoor lights in operation presently.However, municipalities and commer-cial light users are beginning to installthem at a high rate, and the possibilitythat much of the skylight near urbanareas will someday be from this typeof lamp should be considered. Theirlarge numbers of spectral lines wouldpresent a serious light pollution prob-lem. A discussion of projected trends

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for the growth of outdoor lighting ap-pears in the next section.

It is instructive to determine the pres-ent severity of the light pollution prob-lem at observatories. Some of the prin-cipal research observatories in theUnited States listed previously are inreasonably good shape; others, such asMount Wilson, where it is no longerpossible to do broad-band work on thefaintest stars, are experiencing moredifficulty. According to Walker (6),Palomar suffered a zenith light pollutionlevel in 1965 which was only about0.1 magnitude, or roughly 10 percentof the natural light of the night sky.This was contributed to in almost equalparts by Los Angeles and San Diego atquite different distances. At a zenithangle of 450 toward either city, thisfigure rose to 20 percent. At Kitt Peakin 1972, the lights of Tucson are ap-proaching the 1965 level at Palomar;this is far in excess of the most pessi-mistic predictions made before the con-struction of the major telescopes at KittPeak.

Unfortunately, accurate quantitivedata on skylight levels have not beengathered in any systematic way at mostobservatories. There have been only afew programs-for example at KittPeak for the past 18 months and atFlagstaff for the past 10 years-tomonitor sky brightness for urgentlyneeded figures on the rate of increaseof light pollution.

There is a dimension to the problemwhich should not be passed over, andwhich has to do with the phrase "majorresearch facility." By definition, an ob-servatory is a major research facilityby virtue of the fact that competitiveresearch is still possible at its location.For broad-band observations, this is nolonger the case at many older observa-tories in or near major metropolitanareas. Part of the indirect cost of out-door lighting has, for these cases, in-cluded the obsolescence of scientificresearch facilities, usually graduallyover a number of years. Such costs arealmost never considered by the agenciesthat authorize lighting projects.

Growth of Light Pollution

Accurate quantitative information onthe total outdoor illumination in theUnited States as a function of time isnot directly available; one can get roughinformation only from indirect sources.As with many other man-made environ-mental factors, no attention was givento the possible harmful effects of out-

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Light

x ~~~~~~~~~~~~x

E

20 4

1950 1960 1970

Fig. 5. The growth of power consumptiondevoted to outdoor public lighting (bottomcurve), and the light (top curve) producedby that power, for the past 22 years.

door lighting. I am reminded of an alltoo recent statement by Meinel (7), ofthe University of Arizona, who re-marked on observing conditions at KittPeak National Observatory: "Most ofthe city is hidden from view by theTucson Mountains, west of the city. Atpresent, the city's growth potential islimited by the availability of water andis directed eastward because of theTucson Mountains. For the foreseeablefuture there appears to be no seriousthreat to the astronomical conditionsat Kitt Peak." Virtually all would haveagreed in 1960. Staff members at KittPeak no longer take such a sanguineview of the light pollution problem. Infact, they have mounted a vigorous andsuccessful program in cooperation withthe nearby Steward Observatory andthe Smithsonian Observatory to per-suade the city of Tucson to adopt light-ing standards that will alleviate theproblem.

The rapidly growing city of Los An-geles is an astronomical center and istypical of urban-suburban areas acrossthe land. Most of the city streets arelit, and there are many interstate high-ways and freeways, parking lots, build-ings, and outdoor sports arenas that areilluminated at night. On the cover areviews of Los Angeles from MountWilson in 1911 and 1965. They showthe dramatic growth of the city and theproliferation of streetlights, but they donot adequately convey the increasethat has occurred in the level of lightpollution of the sky. It is not only thenumber of lights that has increased butalso the luminous output per lamp. Sim-ilar changing views of many cities couldhave been obtained, but are not readilyavailable. Not even such a simple moni-toring program as photographing the

surrounding land area, say every 5years, has been carried out systematical-ly at most observatories.

Figure 5 is a plot of electrical powerconsumption devoted to street andhighway lighting in the United States,as a function of time (4). Althoughpower consumption for this purpose hasbeen steadily rising, the growth hasbeen approximately linear. For com-parison, an estimate of the total lightproduction as a function of time hasalso been plotted in Fig. 5. This was ar-rived at by using both the power con-sumption curve and the mix of incan-descent and vapor lamps given in Fig.3. The average incandescent lamp ef-ficiency was assumed to be 20 lumensper watt, the vapor lamps were as-sumed to be five times as efficient, andall individual lamps were assumed torequire the same power. This is arough but adequate way of determiningthe shape of the luminosity curve. Itshould be mentioned also that the powersurvey figures are likely to be under-estimates of the total power consump-tion for outdoor lighting, since thesample is presumably incomplete andsince it does not include the very im-portant component of outdoor lightingnot used for public roads, for example,lighting in parking lots.The lumen growth curve has the fa-

miliar exponential form associated withso many environmental factors whichcan result in stresses of some sort. Inthis case it is the scientist who playsthe role of the highly sensitive systemcomponent feeling the stress first. Itmight also be interesting to attempt anassessment of the biological effects, ifany, of outdoor lighting.

In 1970, outdoor vapor and incan-descent lamps existed in roughly equalnumbers. The present installation ratefor new incandescents is essentiallyzero, and for new vapor lamps it is6 to 10 percent per year nationwide,with a much higher rate for the Luca-lox high-pressure sodium lamp. Figure5 shows a rate of lumen growth whichis exponential at an astonishing 23 per-cent per year between 1967 and 1970.An earlier examination of light pollu-tion in California (6) was based onthe assumption that light level and pop-ulation would grow at approximatelythe same rate, but the true rate maybe six to ten times as large.

If total outdoor lighting continues togrow at a rate of only 10 percent peryear, by 1985 the national outdoorlight level will have increased by afactor of 300 percent since 1973. Acompounding factor is that the growth

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is likely to take place simultaneouslywith dispersal over larger suburbanareas. These two factors taken togethermake it not unlikely that some ob-servatories will experience more than atenfold increase in the light level inthe sky by 1985, which will rendermany observations impossible.

Light pollution has been concentratedfor the most part in a few narrowspectral lines of mercury, which areavoidable under some conditions. Thenew high-pressure sodium lamps havea much richer spectrum, and will af-fect some kinds of astronomical re-search more. Thus, astronomy faces apotential hundredfold increase in skybrightness during the coming decade,for some kinds of programs. It is es-sential that astronomers begin to paysome attention to the spectral distribu-tion of commonly used outdoor lamps,especially with regard to their contin-uum emission, and to the proportionof light emitted at the blue end ofthe spectrum. Currently available lampsdiffer tremendously with respect tothese two qualities.What really matters, of course, is

not so much the nationwide pattern ofoutdoor lighting growth, but rather theproliferation of outdoor lighting in theimmediate surroundings of the principalresearch observatories. Such observingfacilities are not scattered uniformlyacross the country, and their distribu-tion is likely to become even more non-uniform in the future. There are a num-ber of factors which determine whethera location is suitable as a site for anastronomical observatory, aside fromthe darkness of the sky. These are (i)the quality of the seeing, which is de-terminated by the stability of the airabove the site; (ii) whether there issignificant air pollution, such as auto-motive smog and smoke from powerplants (smog can increase light scatter-ing during the daytime, adversely af-fecting solar observations, and dust isresponsible for an increase in the at-mospheric extinction of starlight); (iii)cloud cover; (iv) winds; (v) altitude;and (vi) whether the site is on jetroutes, since contrails disturb observing.When all the above factors are con-

sidered, there are remarkably few sitesin the United States suitable for dark-sky observing. They are almost all inthe Southwest. Walker (6) surveyedsites in California for a possible futuremajor facility, and concluded that thefactor of light pollution alone wasenough to rule out more than half theland area of the southern part of thatstate. The other factors narrowed the30 MARCH 1973

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4 8 12Lumens

Fig. 6. Total crime index of the FederalBureau of Investigation as a function oftotal outdoor illumination for the period1960 to 1970. Powers of 10 have beendropped for both the ordinate and theabscissa.

possibilities further. One of the sitesbeing given prime consideration for anew observatory in California is MountJunipera Serra, which is already at theedge of Walker's circle of danger fromlight pollution projected to the year1985. He assumed that skylight wouldgrow at the same rate as population.We have seen that his estimate is un-

fortunately far too conservative. Fur-thermore, his light pollution estimateswere based on measurements at very

few locations and extrapolated to otherlocations mainly on the basis of popu-lation. It would be useful to make ac-tual measurements of sky brightnessfrom a great many locations aroundexisting and potential observing sites.

Causes of Light Pollution Growth

There is a startling difference betweenthe growth rates for population (about1 percent per year) and outdoor light-ing (about 23 percent). There are atleast five reasons why outdoor lightinghas grown faster:

1 ) The suburbanization of theUnited States, caused by conversion tothe automobile as virtually the onlymode of American surface transporta-tion. Areas where the full range ofgovernment services such as education,police and fire protection, water, utili-ties, and sewer service are availablehave grown much faster than popula-tion. The public believes it needs more

outdoor lighting, again principally forthe automobile. The outdoor areas pres-

ently using the most outdoor illumina-tion are streets, highways, and parkinglots. Often such outdoor lighting isleft to burn all night, even when there

is no real need for it. It is common tosee empty shopping center parking lotsshining brightly and uselessly at 4 a.m.

2) Social factors such as fear ofcrimes of stealth and violence have con-tributed to the perceived need. Risingcrime rates have been used effectively(see item 5 below) in promotional ef-forts for increased outdoor lighting.The argument used is that the crimerate will drop where illumination isincreased, and there are some statisticalstudies which are put forward in sup-port of this idea (8). Since such studiesare usually financed and published bylighting equipment industries, they de-serve to be looked at critically. I havetwo examples of how data supplied bysuch groups can be used to draw exactlythe opposite conclusion from that in-tended about the desirability of in-creased outdoor illumination. (i) Ac-cording to (9), only 2 percent of citystreets are illuminated to minimumstandards; 98 percent are underlit. Since(according to the same source) 80percent of crimes occur on streets whichfail to meet the standard, the conclu-sion is that we must buy more lights.However, the opposite conclusion re-sults if one compares the crime ratesper street for the two categories.0.80 crimes per 0.98 dim streets =

0.82 crimes per dim street

0.20 crimes per 0.02 bright streets =10.0 crimes per bright street

Or, crimes are 12 times as likely tooccur on brightly lit streets. (ii) Thereare some studies (8) which connectlight to reduced crime rates. Suchstudies have been confined to a fewsmall areas. If one takes the larger view,considering not individual streets butentire cities or the nation at large, aninconsistency looms. One might ex-pect to find that as the general levelof outdoor illumination rises, crimerates would drop correspondingly. Fig-ure 6 is a plot of the total crime ratedetermined by the Federal Bureau ofInvestigation (10) against outdoorlighting luminosity from 1960 to 1970.The sensationalist statistician with anax to grind might try to use such a plotto conclude that lighting causes crime.The point of these two examples is

not that the unconventional conclusionsare true, but that emotionally based orincomplete information can be used topersuade city councils and private busi-nesses to undertake large outdoor light-ing projects. The selling has obviouslybeen very successful-most people nowbelieve that outdoor lighting buys themsecurity. I suggest that the deeper so-

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ciological roots of crime must be foundand treated, and that outdoor lights willnot only irritate the astronomer, theywill deplete the public treasury pos-sibly without affecting overall publicsecurity in any significant way.

It is possible that any demonstratedreduction of the crime rate in a brightlylit area may be negated as criminalssimply move on to a softer target area.Evidence that outdoor lighting is largelyirrelevant as a factor in residentialburglary is given by the increase indaytime over nighttime crime rates(10). In the decade from 1960 to1970 the daytime residential burglaryrate rose 337 percent, and it now ex-ceeds the nighttime rate. Factors suchas changing life-styles which result inresidences being vacant during the daywould seem to be more important thanillumination.

3) Technological improvements inlighting systems have resulted in lumi-nous efficiencies up to six times higherthan in the recent past.

4) An increase in nighttime businessand recreational activity.

5) A vigorous, well-financed, andhighly effective public relations andpromotional campaign for increasedoutdoor illumination by manufacturersand suppliers of lighting equipment,their trade organizations, and relatedtechnical and professional societies.Foremost in this arena are such organi-zations as the Street and Highway SafetyLighting Bureau, the General ElectricCorporation, and the Illuminating En-gineering Society.

What Can Be Done

Factors that will influence the pro-liferation of outdoor lighting are (i)the rate of growth of the population,(ii) the evolution of zoning practicesand the suburban sprawl rate, (iii)whether there is conversion from theautomobile to public transportation sys-tems, (iv) changes in lighting tech-nology, and (v) esthetic and protec-tive policies that governments mightadopt which will have some bearing onlight pollution. The last item on thislist is the one that seems most likely tohave the largest immediate effect. Mostof the remarks in this section will there-fore concern changes in public policythat reflect scientific needs.Of course, outdoor illumination is

intended for things like cars, streets,parking lots, and buildings, not thesky. All illuminated surfaces, however,have some reflectivity. Dark black as-

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phalt has low reflectivity and light con-crete has a much larger reflection co-efficient. Encouraging the use ofsurface materials of low reflectivity,where possible, would help a little, butthis approach is not likely to be veryeffective.

There is an additional factor of lampdesign: how much light is directeddownward where it will do some good,and how much goes uselessly up intothe sky. The Tucson observatories havegiven much attention to this phase ofthe problem (11), and have persuadedthe city to adopt an ordinance (12)setting regulations on the elevation dis-tribution of luminaires-the amount oflight that can be directed skyward.Lighting fixture standards of the kindproposed are attractive from a politicalpoint of view, since the objective ofkeeping the light on the ground happensto coincide with the objective of thosewho use the lights. There are some situ-ations where this is not the case, forexample, in outdoor sports stadiums.The ordinance also requires that new

luminaires be equipped with filterswhich are opaque to the far-blue andultraviolet lines of mercury, such asthe 435.8-nm line. This element of theTucson ordinance should be consideredfor adoption in all regions where as-tronomical research might be affected.It embodies the concept of reservingfor astronomy a portion of the spectrumtoward the blue end, where visual ef-ficiency is low anyway but where as-tronomical detectors tend to work verywell. This specific ordinance requiresthat luminaires be equipped with filterswhich absorb at least 90 percent ofradiation of shorter wavelength than440 nm.The Tucson example is a valuable

precedent for protection of observa-tional astronomical research. A usefulmodel for regional or even federal pro-tection is the situation for radio as-tronomy. The Federal CommunicationsCommision and international bodiessuch as the World Administrative RadioConference for Space Telecommunica-tions have reserved bands at radiowavelengths for astronomical use. Un-fortunately, the demand for space in thespectrum for communication and navi-gation is so intense that some of thefrequencies used by radio astronomersare not reserved exclusively for astron-omy. To give some additional measureof protection, a radio quiet zone cen-tered on the National Radio AstronomyObservatory in Green Bank, West Vir-ginia, has been established. Thus, thefederal government already has a bal-

anced scheme of radio wavelength emis-sions standards with control over boththe spectral and geographical distribu-tion of sources. It seems a ripe time forthe astronomical community to seekextension of the same principles, per-haps in modified form, to other partsof the electromagnetic spectrum. Anexisting federal agency, such as the En-vironmental Protection Agency, mighttake the responsibility.

Street lighting is primarily for thebenefit of the automobile driver. Since,apart from reasons of crime deterrence,there is no advantage to lighting thestreets where and when automobiles arenot present, most light might be con-sidered to be wasted. It seems worth-while then to consider completely newsystems for lighting streets. Where onlyautomobiles are involved, it might makesense to abolish streetlights and allowimproved automobile headlight systemsto do the same job. High-intensity vaporlamps could be developed for automo-tive use and used in conjunction withpolarizers mounted on car lamps andwindshields, tilted at 450 to the vertical.The headlights in use today are gener-ally recognized to be inadequate fornighttime driving at high speeds, butif their luminosity were increased by afactor of 20 or so much of the needfor perpetual nighttime lighting woulddisappear. The total amount of lightproduced would probably be much lessthan at present, although the fact thatit would be horizontally directed istroublesome. A study of the effective-ness of any such system should includethe light pollution aspect.

It is possible to make significantprogress toward protecting the astro-nomical observing environment withoutcompromising the legitimate lightingneeds of the public. Minimum standardscontrolling the elevation distribution oflight from individual lamps and thespectral and geographical distributionsare feasible and should be sought whilethere is time to preserve useful observ-ing sites.The scientific community can make

an immediate contribution. Every majoroptical observatory in the countryshould initiate a routine program tomonitor the skylight as a function ofposition, wavelength, and time. It isessential that astronomers arm them-selves with hard data on deterioratingobserving conditions so that effectiveremedial action can be sought and wonin the future. Some progress can bemade by formulating the problem quan-titatively, and by increasing communi-cation on this subject in meetings such

SCIENCE, VOL. 179

as the one organized by project ASTRA(13).

Finally, esthetic arguments againstuseless outdoor lights are beginning tobe appreciated. The chairman of theLos Angeles City Planning Commissionactually proposed in 1972 that theSanta Monica Mountains be outfittedwith many searchlights to scan the skiesevery night, for their dramatic effect(14). Public outrage was instantaneousand nearly unanimous. But aside fromthis isolated and somewhat bizarre inci-dent, there is some growing feeling thata dark night sky is a nice thing; millionsof urban children have never seen theMilky Way. In 1971, the board of di-rectors of the Sierra Club adopted a

policy against unnecessary outdoorlighting because it wastes energy, isesthetically unpleasant, and interfereswith astronomical research. This pointof view should be encouraged.

Summary

There have been major qualitativeand quantitative changes in outdoorlighting technology in the last decade.The level of skylight caused by outdoorlighting systems is growing at a very

high rate, about 20 percent per year

nationwide. In addition, the spectraldistribution of man-made light pollu-tion may change in the next decadefrom one containing a few mercury

lines to one containing dozens of linesand a significantly increased continuumlevel. Light pollution is presently dam-aging to some astronomical programs,and it is likely to become a major factorlimiting progress in the next decade.Suitable sites in the United States fornew dark sky observing facilities are

very difficult to find.Some of the increase in outdoor il-

lumination is due to the character ofnational growth and development. Someis due to promotional campaigns, inwhich questionable arguments involvingpublic safety are presented. There are

protective measures which might beadopted by the government; thesewould significantly aid observationalastronomy, without compromising thelegitimate outdoor lighting needs ofsociety. Observatories should establishprograms to routinely monitor skybrightness as a function of position,wavelength, and time. The astronomicalcommunity should establish a mecha-nism by which such programs can besupported and coordinated.

References and Notes

1. A. L. Broadfoot and R. Kendall, J.

Geophys. Res. 73, 426 (1968).2. C. W. Allen, Astrophysical Quantities (Athlone,

London, 1955); 1 stilb = 1 lumen per squarecentimeter per steradian = 1.15 X 10 stars ofvisual magnitude 0 per square degree.

3. W. A. Baum, in Astronomical Techniques,W. A. Hiltner, Ed. (Univ. of Chicago Press,Chicago, 1962), p. 1.

4. Street and Highway Lighting Committee, AReport on Street and Highway Lightingthroughout the United States (Edison ElectricInstitute, New York, 1970), p. 15.

5. Census of Manufacturers (Bureau of theCensus, U.S. Department of Commerce, Wash-ington, D.C., 1954, 1958, 1963, 1967).

6. M. F. Walker, Proc. Astron. Soc. Pac. 82,

672 (1970).7. A. B. Meinel, Stars and Stellar Systems (Univ.

of Chicago Press, Chicago, 1960), p. 54.8. Joint Committees of the Institute of Trafflo

Engineers and the Illuminating EngineeringSociety, Illum. Eng. New York 59 (No. 9),585 (1966).

9. Street and Highway Safety Lighting Bureau,5 Reasons and 18 Ways to Improve YourStreet Lighting (Street and Highway SafetyLighting Bureau, New York, 1969).

10. Crime in the United States (Uniform crimereports, Federal Bureau of Investigation,Washington, D.C., August 1971), p. 65.

11. The Steward, Kitt Peak National Observatoryand Smithsonian Astrophysical Observatory,Light Pollution: A Threat to Astronomy inPima and Santa Cruz Counties (Stellar Di-vision, Kitt Peak National Observatory, Tuc-son, Ariz., 1971).

12. City ordinance number 3840, Tucson, Ariz.,adopted 5 June 1972.

13. N. Laulainen and P. W. Hodge, Eds., Astron-omy and Air Pollution (Project ASTRA Publ.No. 15, Univ. of Washington, Seattle, 1972).

14. Los Angeles Times, 17 May 1971, part II, p. 1.15. I would like to acknowledge useful discus-

sions with, and comments on the manuscriptby L. Aller, L. Blakeley, H. Epps, A. Hoag,E. King, D. Popper, T. Riegel, R. Roosen,M. Walker, and R. Weymann.

years should see a rapid expansion ofour knowledge in this field, and thetime seems appropriate for us to takestock and see just where we are.

The Genetics of HereditaryDisorders of Blood Coagulation

Functional and immunological studies provide evidencefor the heterogeneity of many familial clotting disorders.

Oscar D. Ratnoff and Bruce Bennett

The dramatic nature of the symp-

toms of hereditary disorders of bloodcoagulation and the ease with whichthe affected tissue, circulating blood,can be studied contribute to the dis-proportionate interest in these rare

conditions. Among the results of many

published studies, a large volume ofinformation has been generated whichsupplies support for principles of he-

30 MARCH 1973

redity adduced from other sources.

The discovery that many of these dis-eases are heterogeneous in nature hasoverthrown our simplistic views andhas raised, in the usual way, more

questions than answers. The next few

Normal Blood Coagulation

In mammals, blood clotting resultsfrom the conversion of a solubleplasma protein, fibrinogen (factor I),into fibrin, an insoluble network offibers. The jelly-like appearance ofblood clots is due to the entrapmentof cells and serum within the meshesof this network. The formation offibrin is catalyzed physiologically by a

hydrolytic plasma enzyme, thrombin,which cleaves two pairs of small poly-peptides, fibrinopeptides A and B, fromeach fibrinogen- molecule (Fig. 1).What remains, so-called fibrin mono-mer (1), then aggregates into an in-soluble polymer, fibrin. The monomericunits of fibrin are further bound cova-

lently through the action of another

Dr. Ratnoff is professor of medicine, Case Western Reserve University School of Medicine andCareer Investigator of the American Heart Association, University Hospitals of Cleveland, Ohio 44106.Dr. Bennett is research fellow in medicine, and fellow of the Pink Family Foundation, Case WesternReserve School of Medicine.

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