No one likes light pollution, obtrusive light, or nuisance light. It affects people, animals and plants, it wastes energy, and it is completely avoidable. The ILP’s world-renowned guidance on the reduction of obtrusive light was updated in 2020 and in our free CPD session, we invite all lighting engineers, designers, consultants and manufacturers to:
- Allan Howard BEng (Hons) CEng FILP, panel chair, presents the latest GN01 Guidance Notes for the Reduction of Obtrusive Light 2020.
- Understand Table 4 and follow an example approach for calculating light intensity.
- Learn from Emily Bolt BEng (Hons), to discover practical information on what type of products to apply in what situations, available from many manufacturers.
Q&As
| Question / Comment | Answer |
| A decree by the French government issued in late 2018 seems to focus on CCT rather than CRI to tackle light pollution. Do you think they should set limitation on CRI instead? | It’s a balance between the CCT and the CRI depending on what you are trying to achieve and the area you are looking to light. So in the example I gave there was a restriction on using LED with any blue light so the only way to go to LED was to use an amber LED, the solution provided was better than using an amber LED but it’s more like a SOX solution where you would have a low CCT and low CRI. It is probably right to focus more on the CCT as the CRI for road and street areas as in most cases you would want better CRI. |
| Amber LED 1700k CRI 37 what would be the SPR and what effect does this colour temperature have on efficacy? | Generally, the SP ratio would be less than 1 and the efficacy would normally be less than 100lm/w, but you would not install this in an area where you are looking at saving energy. It is a specific solution for areas where there are sky glow restrictions. |
| As a Dark Sky reserve, we are struggling to secure a *trusted* supplier of Dark Sky Friendly lighting fixtures and fittings. It would be helpful to create a UK ‘catalogue’ of suppliers we could give to developers during the planning process confident in the knowledge it would be the correct light. | Whilst there are many luminaires on the market that would suit dark skies they are only as good as how they are installed. If the installer does not understand how to mount and aim them then even the best performing luminaire will perform poorly. A main problem area is the domestic security market and the failure of the likes of B&Q to really supply suitable fitting and not to sell poor ones such as the up/down porch lights. |
| As most ILP guidance seems to begin from the presumption that lighting is necessary, will the ILP give clear guidance on when light is not necessary or beneficial (see LANTERNS report by London School of Hygiene and Tropical Medicine and staff at UCL Department of Security and Crime Science for example) and in so doing, support local authorities in particular in seeking to prevent useless lighting running along the road network through rural or otherwise dark areas? | The first question in any lighting consideration should always be does it need to be lit? The guidance then looks at how best practice can then be considered to achieve the most appropriate lighting installation for the task and environment, using competent lighting designers and contractors. |
| Diagram is poor on definitions terms slide. The shape of the light would mean that light would fall to the left of the light like it did to the right. You should have included proper diagrams. | The diagram is just indicative and is one that is used in a lot of reference documents, the shape of the luminaire has no relevance to the discussion within the diagram. |
| Environmental Zones. You should have used the term ‘intrinsically dark’ in this table as that is what is used in the NPPF. | The term intrinsically dark means different things to different people and there are some tables that reference this to meaning and E0 zone and others reference it to an E1 zone. This has caused confusion and thus is was removed and replaced with more tangible descriptions. |
| How can we encourage more lighting manufacturers/suppliers to photometrically test luminaires with gamma angles 0-180 degrees? Many luminaires are only being tested to 90 degrees, with some software in turn stating a ULR of 0% when this is not accurate, as light has not been measured above the horizontal. | Definitely a challenge and an aspect that we are starting to pick up and comment upon within guidance documents and standards. |
| How does the limit on skyglow apply to very large media walls/facades – how should luminance be considered so as not to create obtrusive light on to other properties and to avoid a large portion going directly into the sky? What are your thoughts on the dynamic effects of these features; minimal levels of light obtrusion could still be considered a nuisance if the light source is constantly changing in terms of spectrum and intensity. | This is a topic being considered by the CIR technical Committee TC4058. Allan Howard allan.howard@wsp.com is the UK representative on this panel and would be happy to discuss current thoughts on how such displays should be designed such that the image only is seen by the intended observer and also the limitations being considered on display type, intensity and so forth. |
| How is an astronomical observatory defined? If used mainly for, say, public outreach in a DS area, does that count? | The CIE document reference optical observatories, there is no real comment on how they are used. |
| How is the industry going to pro-actively manage/eliminate light pollution in a post pandemic society where more pressure will be on local authorities to rethink how they deliver 24/7 city and public realm environments where light will be an intrinsic requirement? | We have seen a much greater awareness of the impact of artificial light over the years and some local authorities are now developing lighting master plans with a view to how artificial light can be controlled to suit the local task need and environment. What is missing is how internal light from offices, shops, retail and so forth should be managed – as I understand it Part L requires the lighting designer to design the installation such that the light is contained within the building and that the building occupier/owner understands how to control and use the lighting – is this always the case, evidence in the street and night skylines may suggest not. This of course does not cover residential lighting. |
| How would you anticipate compliance with intensity where an LED lantern in residential area of small “diameter” and a much closer proximity (<5m) to maintained viewpoints. Or recommend use of maximum lux as a guide? | There are two metrics for consideration, one is vertical illuminance (lux) which has its own limits and then there is intensity which needs to be determined using table 4 as discussed. |
| If the viewer is in an E2 zone and the installation is in an E3 zone, what range is used? | If the installation is close to the boundary of the zone then it should be designed to the requirements of the E2 zone. |
| If we are moving to amber LEDs, why not get greater efficiency by using low pressure sodium? | You could do this is just one possible solution maybe the local authority wanted the longer lifetime of the LED so they had less maintenance. |
| I’m from Barcelona. In Catalonia we have public measurements of SQM in this webpage: http://mediambient.gencat.cat/ca/05_ambits_dactuacio/atmosfera/contaminacio_luminica/avaluacio-qualitat-cel-nocturn/ | Many thanks. |
| Light intrusion to an individual can be subjective and regardless of any mitigating measures does not address the concerns which leaves designers in a grey area as you can’t design to an individual’s requirements. | This is of course true and the research that supports the guidance looks at what would be acceptable to 90% of the population and some people are more sensitive to light than others. Also, the age of the observer has an affect with younger observers being more sensitive to intensity to say much older people. |
| Light pollution is caused by poor design, and the accepting of those designs by authorities. | Alas a lot of local authorities do not have lighting professionals within their organisations and some planners / environmental teams do not necessarily refer to a competent lighting professional when making assessments. |
| Only so much planning can do. People can do whatever they want regarding lighting without permission. | True, the current considerations to be made for planners are advised in GN01/20. |
| Permitted planning development is a real problem. It doesn’t allow for any decent control for what could be very damaging lights. | True, the current considerations to be made for planners are advised in GN01/20. |
| Should we consider sky glow in isolation or should at the same time consider fauna impacts when considering the light source in the first place? | The designer needs to consider all aspects when looking at a design, the choice of light source and then how this source should be controlled to mitigate any adverse effects. |
| Skyglow isn’t only an urban problem = it can be experienced in very rural areas. | I fully agree and it is perhaps most noticed from the rural areas. |
| What is the definition of ‘intrinsic’ then? Not above 20? | The term intrinsically dark means different things to different people and there are some tables that reference this to meaning and E0 zone and others reference it to an E1 zone. This has caused confusion and thus is was removed and replaced with more tangible descriptions. |
| SQ data tends to be concentrated on Dark sky reserves as this was a requirement of designation. | Noted. |
| SQM – the meter has a tolerance of 10%. A reading of 20 could realistically go to E0/E1 or E2. It’s not a great metric. | It is a measure that is currently used, as with all measurement instruments they have a tolerance and the process will also have various uncertainties – the same applies with illuminance meters which at best are 6% accurate and others can be 10 to 15% or worse. The key aspect is that those using such instruments should be competent in their use and how the results are advised, they should have a value +/- %. |
| SQM info available at www.lightpollutionmap.info. | Thank you. |
| SQM s are calibrated. to +/-.05 mag/arcsec^2. | Thank you – again those using such instruments should be competent in their use. |
| The ‘intrinsic’ darkness definition runs in conflict to the recent IDA changes of what ‘intrinsic’ is. | The term intrinsically dark means different things to different people and there are some tables that reference this to meaning and E0 zone and others reference it to an E1 zone. This has caused confusion and thus is was removed and replaced with more tangible descriptions. |
| There are two types of SQM (Measurement fields). Are either ok to be used or is there a requirement to use the wider or narrower field to demonstrate compliance with GN01:2020? My understanding is the narrower field is for where you have objects or light sources in close proximity. | That sounds sensible but I am not in a position to advise. As with all measurement instruments they have a tolerance and the process will also have various uncertainties – the same applies with illuminance meters which at best are 6% accurate and others can be 10 to 15% or worse. The key aspect is that those using such instruments should be competent in their use and how the results are advised, they should have a value +/- %. |
| Is Philips developing technology for luminaires to switch to amber LED dynamically if bats are detected? Could you also please expand how the amber LED lighting spoken of meets CRI >60? | No not at the moment. The solution for Bat sensitive areas is not amber LED see the info on the link below. It is a specific light source to help mitigate the effect of a certain species of bats and the amber LED doesn’t meet CRI >60. It’s not to be used everywhere in the example I gave you and could not use a light source with blue light content that was a stipulation of the country. The idea is to use it in areas such as national parks for example so E0 where some areas need to be lit but preserving the night sky is the priority over colour rendering. https://www.luxreview.com/2019/09/02/unveiled-the-uk-s-first-bat-friendly-highway/ |
| We are working on a commercial shopping centre in an E3 zone. The facade design and solution we are planning to uplight using inground uplights as a feature/decorative element. There are no other ways we can light it. The old guide acknowledged there will be some lighting schemes that will not be able to avoid this. It states that as long as you take care reducing the upward light where possible through directional lights and accessories it is ok. This is what we plan to do to reduce as much as possible direct light upwards but some is unavoidable being an uplight scheme. What is the new guidance in the new guide on these types of special cases where upward light cannot be avoided? Is this still ok to do this? | We still would advise this; a competent lighting designer and contractor would be able to develop the right solution. |
| Weather plays a significant role with SQM measurements. | Noted, hence why a competent person should undertake the measurements. |
| What is pre and post curfew? | Curfew is a time that a local planning department may consider then the artificial lighting should be turned off or perhaps dimmed. 23.00hrs has been quoted as a general time in the past but it is up to each planning authority to consider a lighting installation on its own merits, where it sits, the mix of observers and so forth so curfew such as 21.00 can be common when looking at sports facilities. |
| What is a recommended method for obtaining SQM for a site/area? | A competent person who understands the instruments to be used to measure the SQM and how to understand and process the readings needs to undertake the measurements. I would assume that the likes of CfDS can advise on those who are competent to undertake such measurements. |
| When do we anticipate the release of GN01:2020? | GN01/20 has been published and the update which provides more guidance on the use of table 4 and some other aspects of the document will be issued in the next couple of months. https://theilp.org.uk/publication/guidance-note-1-for-the-reduction-of-obtrusive-light-2020/ |
| When is PLG 04 likely to be updated to include further guidance and updates required following guidance note 01/20 release? | PLG04 is under review at this time, as with most documents of this type. It is being delivered by volunteers in their own time so at this time a definitive date cannot be advise but progress is good. |
| When you said a design and assessment should take account of the neighbouring installations, are you recommending a baseline survey be undertaken for each project? | Yes, the document advises that a full baseline assessment should be undertaken. |
| Where do we find reputable SQM data to use? | I would suggest the CfDS would be a good starting point or your local astronomical observatory organisation. |
| With internal louvres fitted into the luminaires, will there be increase in light above 90 degrees? | No fitting an internal louvre into a product will not increase the light above 90 degrees. |
| www.lightpollutionmap.info that data hasn’t been collected using a unihedron SQM meter. I think its satellite and modelling data. | Thank you. |
| You mention that UFR is only applicable where the installation is in proximity to observatories, or within E1 zones abutting E0 zones, but CIE 150 suggests that it is used for all installations consisting of four or more luminaires. Therefore, how cannot calculating UFR be justified? Also, is any software currently capable of undertaking this calculation or does it need to be carried out manually? | CIE150 does not make that statement, yes it advises on 4 or more luminaires but then goes on to discuss when there are optical observatories within proximity of the site and so forth for when it should be considered. There is not really any software that exists and the reflectance of surfaces depends upon climatic conditions, dry, wet, snow, frost etc, plus also the state of the surface as such the uncertainties are so great any calculation could be considered meaningless. |
| Emily said that “modern LED luminaires have a flat glass and a light distribution that limits light above the horizontal. The luminaires would have a cut-off or semi cut-off light distribution arrangement. The optic design would be such that no light is emitted at an Imax of 95° and very little light, if any, distributed at Imax of 90°”. Several years ago in discussions with the Campaign for Dark Skies, I recall them saying that the main cause for skyglow was the distribution of light in the small area between 90° and 95° (just above horizontal). I presume this is the case and that we should therefore only be looking at luminaires distributing absolutely no light above the horizontal. Could a view on this be given? | In the new guidance the notes under table 7 give values of less than 0.5cd/1000lm between I90 and I100 for sky glow in areas around observatories so yes this has been taken into consideration in the new standard. From my experience most road and street luminaires if mounted at 0deg tilt will provide Imax90 and Imax95 of 0, and generally at 5deg the Imax 95 is always 0 with very little light at Imax 90 if any. Obviously if you install at a great tilt angle this may change. If you want to limit sky glow then when you are designing with a luminaire you can check the G* classification and generally this shows the Imax 90 and Imax 95 values and these will change with the tilt of the luminaire. |