I am a US citizen (with a British wife) who has lived and worked in the UK for the last 16 years.

  I have a BS and MSc in Geology with a minor in Physics, and I currently work as a technical author, writing computer manuals for the oil industry.

  I became seriously interested in astronomy about five years ago, and have been Chairman of the Maidenhead Astronomical Society for the past three years.

WHAT HAS BEEN THE IMPACT OF LIGHT POLLUTION ON UK ASTRONOMY?

  4.  In the past five years in which I have been active in astronomy I have seen the night sky turn from black to greyish yellow due to wasted light shining directly into the sky from street lights, sports venues, security lights, and floodlighting for buildings, and have seen several observing sites become unusable because they have been overtaken by skyglow or have become overlooked by blazing security/yard lights.

  5.  The last time I took my children out to a field near their school to see a comet that was on view, we didn't see anything because (1) A nearby home owner had installed an extremely powerful, horizontally-directed 500 Watt security light which shone directly onto our viewing site, which is a public footpath in a greenbelt area, so our eyes could not get dark-adapted, and (2) The comet's position in the sky was behind a column of light pollution which was projected skyward from a farmer's yard light. My children came home disappointed, and I came home infuriated that a handy dark-sky site that I had previously frequented was now permanently ruined by two extremely bright lights. The home owner's light (12 Forty Green Drive, Marlow) is now on every night (shown below, circled) (not printed).

  6.  The limited brightness range of the printed image above does not show the true brightness of the light well, but I can assure you that when viewed in situ it is like standing in the headlight beam of a car. (It is so painfully bright that it also prevents anyone from seeing a burglar next to the house, a fact which the home owner has missed completely.) About 30% of the light falls onto the home owner's property, 30% onto the surrounding properties, and 40% directly into the sky. In my experience these are typical proportions for a standard 500Watt garden/security light which has a 180º light spread (both vertically and horizontally). I hear stories like this again and again from my astronomical friends, and there are currently no laws to stop this happening.

  7.  The modern trend towards more light everywhere also has some unexpected physiological consequences for would-be astronomers. One of my astronomical colleagues has noticed that some young people which come to public star-gazing sessions cannot see faint objects at all through the telescope. The only explanation he could offer (which is unproven but sounds reasonable) was that because these young people are constantly in a lit environment—even at night and when asleep—they have lost the ability to become dark-adapted. They couldn't take up astronomy even if they wanted to because their pupils can no longer open to their full diameter, similar to those of a seventy-year-old.

ARE CURRENT PLANNING GUIDELINES STRONG ENOUGH TO PROTECT AGAINST LIGHT POLLUTION?

ARE PLANNING GUIDELINES BEING APPLIED AND ENFORCED EFFECTIVELY?

  8.  I have grouped these two questions together because I don't know the answer. So many new poorly designed lights have been installed in my town of Marlow recently that it is difficult to tell if Wycombe District Council has any lighting guidelines whatsoever, or if any of them are being enforced at all.

  9.  The next table summarises the new lighting installations near my house that have been installed within the last three years. I have only included the ones which to my knowledge are on all night. I have not included numerous new garden lights which, although poorly directed, are triggered by infrared motion sensors and are off most of the time.

  10.  The above lighting is, of course, in addition to the existing light pollution from football pitches, rugby pitches, and car dealers. In my experience these three types of commercial/organisational ventures are the worst when it comes to light pollution, closely followed by street lighting and floodlit commercial buildings, pubs, and hotels.

IS LIGHT MEASURABLE IN SUCH A WAY AS TO MAKE LEGALLY ENFORCEABLE REGULATORY CONTROLS FEASIBLE?

  11.  Yes. This answer is easy, because light is a vector that has direction. This lies at the very heart of the problem, and indeed the very definition of light pollution, which I would define as light which is directed where it is not wanted. The person or organisation who lights a garden or building or street wants just that—to light the object. He does not intentionally want to light the sky or surrounding properties as well—this is just an unfortunate side-effect which he ignores or is unaware of. Whether or not there is stray light being produced makes no difference to him one way or the other. The neighbour or astronomer who bears the brunt of that stray light doesn't want it. These two "opposing" viewpoints are actually 100% compatible; all that is needed is a law to eliminate the stray light, based on its direction.

  12.  For the purpose of preventing skyglow, light pollution control would be very easy to enforce if the law was based on lighting direction relative to horizontal, rather than luminance or some other quantity which is difficult to measure. The direction of horizontal has special significance for many reasons.

  13.  Light shining directly into the sky, above the horizontal, pollutes the night sky more than any other lighting. Of course, downward-directed lighting results in some light being reflected back up into the sky from the ground, but the amount of reflected light is tiny compared to that coming directly from the source.

  14.  Generally speaking, light which is directed below the horizontal is useful, and light directed above the horizontal is not. In the vast majority of outdoor lighting cases, light shining above the horizontal is wasted light. If home-owners and businesses were forced to rotate their existing security lights downward to the horizontal, full cut-off position, outside of the improvement nobody would notice the difference. But to astronomers it would make all the difference.

  15.  Objects that are high up, such as buildings, can be lit from above instead of from below. Special dispensation could be granted in those few situations in which upward lighting can be justified such as air traffic control or certain public monuments for which lighting from above is technically impossible.

  16.  The pub shown below (The Red Lion, Hurley) is lit from below, by a ridiculously high total of 17,000 Watts, pointed straight up into the sky. This would otherwise be an excellent dark-sky site. (not printed)

  17.  The pub shown below for comparison (Duke of Cambridge, Marlow) (not printed) is lit from above. The lights are tilted down so far that they barely shine off the property. The total amount of light shining directly into the sky is only about 30 Watts, coming from the light on the extreme lower right, yet the pub is just as pleasantly lit as the Red Lion shown previously.

  18.  Horizontality is very easy to measure, even by eye from 20 metres away. For most cases you can identify a full-cut-off light fixture by looking at it, and you can tell if the face is horizontal by looking at it side-on from several metres away.

  19.  The above example (Platt's Garage of Marlow) (not printed) shows that the light (flat-faced with 180º spread, circled) is 52 degrees from horizontal, and will therefore shine about 29% of its light directly into the sky. This is very easy to measure on the spot, in situ, by holding a protractor up to your eye. You don't need a light meter, a measuring tape, or a ladder, and you can do it during the daytime in a matter of seconds, and measure hundreds of lights this way in a single day.

  20.  Tilting the light in the previous example down to horizontal would help save the night sky for astronomers and put more light onto the forecourt for the garage. The edge of the forecourt (which the owner is attempting to illuminate by pointing his light directly at it) would see very little change in brightness due to the evenly distributed spread of the light over the 180º range of the light. But without a light pollution law this sensible alternative is not going to happen.

  21.  There is also no point in allowing lights to shine "just a little bit above the horizontal", as this low-incident light is just as damaging as light pointed straight up because it passes through a greater volume of atmosphere. The next diagram illustrates this point. If we take as an example the atmosphere of the Earth: if the entire column of air was compressed to the air pressure at sea level, the atmosphere would only be five miles thick.

  22.  Light travelling straight up goes through (and pollutes) five miles of atmosphere. Light that is close to the horizontal direction passes through (and pollutes) proportionally more miles of air before it, too, ends up high in the atmosphere and goes out into space. The exact numbers are more complicated than those shown in the diagram because the atmospheric pressure is actually a continuous gradient until it thins to nothing, and the curvature of the earth's surface becomes significant at larger distances, but the point stands.

  23.  I was appalled to find out that the guidelines issued by the Institute of Lighting Engineers allow more light to be "spilled" above the horizon in urban areas (up to 25% wastage) than in dark-sky country areas (up to 5% wastage). This is equivalent to saying that in densely populated areas (which are harder on the environment anyway) each building is allowed to waste more light than those in country areas. I see no reason to allow this. To allow a higher light wastage per building in urban areas is simply accepting defeat. It is also a circular argument, effectively justifying light pollution in an area because the area is light-polluted. Because of the higher population density in urban areas, the increased opportunity for light trespass and the increased opportunity for public lighting that is shared between residents means that urban areas should have a lower light allowance per building—not more.

  24.  Low-incident light from cities also extends far into the contryside, as shown in the previous diagram, which is another reason why urban restrictions on light pollution should be no weaker than countryside laws.

  25.  The famous night-time satellite pictures which show the amount of wasted light coming from Britain are misleadingly conservative because the pictures only show light coming from near-vertical sources. The pictures do not show the low-incident lighting which is just as common and just as damaging.

  26.  Although horizontality might be good enough basis on which to prevent skyglow, it is not enough to prevent light trespass.

  27.  My neighbour has some very good horizontal-cut-off lights. One of the lights, however, shines just over my fence, producing a one metre wide band of light across my patio and making it unsuitable to set up a telescope for night-time observing.

  28.  I kindly asked them to point it just a few more degrees down, explaining that for astronomy purposes I'm trying to make my back yard as dark as possible. They were sympathetic and with the best of intentions kindly offered instead to turn it off when I am observing, but if they forget to turn it off when going to bed this means calling them very late at night, or if they go out and leave it on for security purposes then I am out of luck. If they pointed the light just a bit further downward to keep it on their side of the fence then the problem would be fixed permanently, instead of needing to be "fixed" every time I want to observe.

  29.  Unless bright lighting is legally restricted to shining onto the owner's own property, the dual problems of light trespass and skyglow will continue to grow.

  30.  Luminance measurements might be relevant in special high-intensity lighting situations such as locations near sporting venues, or in countryside situations where the amount of light falling on the ground might adversely affect the natural world (where 80% of all animals are nocturnal). But for most cases such as garden and security lights for homes and businesses, luminance is not an issue as long as the light is not shining directly above the horizontal or onto the neighbours' gardens or windows.

ARE FURTHER CONTROLS ON THE DESIGN OF LIGHTING NECESSARY?

  31.  Yes. Well-designed lighting is very difficult to find for home-owners and businesses. The excellent star-friendly revolution in large commercial lighting fixtures has largely been ignored by the major hardware shops such as B&Q. On my last visit to the large B&Q store in Slough, I looked for a full-cut-off light for my own back yard and they didn't have any! All of the lights were poorly designed and had instructions for installation giving 30% light wastage above the horizontal. Most of the lights with built-in sensors could not even be tilted down to full cut-off position. Those which could be tilted to horizontal were not designed to do so and stuck out too far from the wall, and in any case were far too bright.

  32.  Even their "low light pollution astrolight" (which admittedly is an improvement) turned out to be just a repackaging exercise of an existing light, which still wasted 16% of its light above the horizontal. This "low light pollution" light had a poor bracket design which, for no reason, limited the tilt so you couldn't point it downward to full cut-off position even if you wanted to.

  33.  If these super-bright poorly-designed security lights aren't outlawed then there is nothing to stop everyone in my town from eventually getting one (which they are doing, one by one, relentlessly), destroying the night sky, and lighting up their neighbours' yards.

  34.  Some of the large lighting installations such as sports venues can be controlled because they require plannining and consulting, and have started to take advantage of highly-engineered, well-focussed lighting. But to control thousands of home-owners and businesses who have just returned from a trip to the DIY bad lighting store takes more than friendly suggestions. It takes a law. Otherwise all the little lights add up.

  35.  Design alone is not enough, however. The lights have to be correctly installed.

  36.  In most of the public car parks in Marlow, Wycombe District Council have replaced many of the lights (about 10 in all) in a similar way—with horizontally-designed lighting which has been incorrectly tilted upwards at about 70º (or simply mounted vertically at 90º) when installed.

SUMMARY

  37.  In my opinion, a law which will have the most beneficial effect for the environment, inconvenence the least number of people, and be the most welcome and workable for both the general population and for astronomers is one which requires any light stronger than, say, 60 Watts to be restricted in its direction to the owner's property. The actual wording of the law should probably quote some value for lumens rather than Watts, as the efficiency varies greatly depending on the type of bulb. In most cases except uplighting, this can easily be achieved by tilting existing lights downward because most of them are on rotating brackets. Lights which cannot tilt downward far enough can be shielded or replaced, as the cost of the lights compared to that of the building is microscopic.

  38.  On a different note, the wasted energy that it takes to produce the wasted light (equivalent to one entire power station in the UK) adds to the CO2 emissions and global warming. In regard to the Kyoto agreement, the UK can show their sincerity by starting with a law against light pollution.

  39.  On a final note, I would like to say that astronomers are not the only people who enjoy looking at the night sky, but we are losing it quickly. Without a law to protect it we've only got a few years left. According to my children (after their thwarted comet viewing), we have already lost the night sky and it will take a law to bring it back. A law against light pollution is long overdue. I can think of no other planet-trashing practice which is so widespread and yet so easily preventable, so glaringly obvious and yet so ignored.

April 2003