GN01/20: Preventing obtrusive light – Put that light out!

The issues around artificial light at night and at times by day are many and varied. This webinar looks at the various effects and concerns over artificial lighting installations. It will discuss and inform regarding the guidance, standards and regulations that are in place for planners, environmental officers, designers and installers to follow and consider to ensure everyone is managing all obtrusive lighting effects and concerns.

This event is a precursor to the launch of the ILP online training course ‘Preventing obtrusive light – Put that light out!’ and follows on from the previous GN01/20 launch webinar in July of this year. The course will be available from the ILP training platform soon, with discounts for ILP members.

Speaker: Allan Howard, BEng(Hons) CEng FILP FSLL, Technical Director for Lighting at WSP

Host: Seán Campbell, Chair for ILP Ireland and members of the Committee


Is there any prior knowledge needed to join the course?
No, the course has been designed to inform those with little if any knowledge of obtrusive light through to experts where some aspects may be re-enforcement of their knowledge or perhaps new to them.

Does the course cover the issues contained in the UK Government document due to be launched later today?
No, the course was developed prior to this but looking at the points in the ten point plan the course does look to how they can be addressed although they are not mentioned.

This is UK centric, is the planning system in Ireland a similar

The systems are all very similar, England, Wales, Scotland and Northern Ireland have different tweaks on the same aspect. Ireland also has similar processes; the only difference may be the national planning policy aspects but apart from that the principals apply internationally.

When do we think ILP PLG 04 will be updated to include
guidance on new GN 01/20 update?

PLG04 is currently under review and had stalled. However, there has been a lot of progress recently so completion can be expected in 2021.

What areas of CIE150 & CIE126 are missing from GN01?
GN01/20 and the revision due in 2021 pick up the majority of aspects but not in detail, the CIE have been kind enough to permit the ILP to duplicate the tables but the CIE documents have a wealth of supporting information. CIE documents are available for CIE members at a 66.67% discount, the ILP being a major supporter and member of CIE-UK are able to advise ILP members of the discount code so they may in turn purchase these documents at the discounted rate.

Are the requirements of the new GN01 retrospective to existing installations?
Not really, or certainly would not relate to any previous planning applications approved under previous guidance. They may be applied for new developments near to existing lighting installations where the term ‘coming to a nuisance’ may apply.

Could GN01 be clearer on assessing Luminous Intensity?
The revision of GN01 being finalised looks at examples of this, the approach is  laid down in CIE150 and intensity is a factor of the illuminance received at the observer multiplied by the square of the distance, a factor previous nuisance did not take into account with a one value fits all approach. CIE150 has been in existence for many years and lighting software is only just catching up. The revised GN01 looks at how this may be approached.

Does the ILP have an input into the APPG for Dark Skies, reported today ?

Yes, ILP responded to the production of this document along with around 170 others! Commentary from ILP has been accepted and included in the final version which also carries the ILP logo.
Do you think the change to LED is helping to reduce Skyglow,
or do you think that the use of higher CCT (4000K instead of
2700 or 3000K) is causing more of a problem?

LEDs and white light sources certainly seem to have a higher level of reflectance of airborne particulars, you only have to compare white light installations in light fog with SON or SOX installations to see this. The main problem from an obtrusive light perceptive is that the guidance mainly worked with lamp based technologies but with LED luminaires their performance is perhaps not the same and various LED luminaires fail to meet the obtrusive lighting performance requirements. It is not a matter for the guidance to change to suit new light sources as some have suggested / requested but for the luminaires and optics to be designed to meet the requirements.

If the vertical illuminance is over the recommendations, does
that mean no more illuminance or can there be orders to remove existing installations?

In a word yes – if the level of illuminance is greater than that permitted for the class at the time of night then the occupier of the premises could raise a nuisance claim. If the problem is clearly caused on one lighting installation then the owners / operators of the system would be required to rectify the problem (supplying curtains is not a solution, the course has to be sorted), the problem comes if there are a number of existing installations contributing to the high level and determining which should be resolved.

What is the curfew?
The time after which stricter requirements (for the control of obtrusive light) will apply; often a condition of use of lighting applied by a planning authority, it may be that the lighting is required to be turned off after a defined time or it has the change to a different performance level, for example a car park when less busy could have the lighting level reduced to the next lowest class at a defined time.

Tricky to access windows to measure existing light levels,
so how do we model all light sources if local inventory for
existing lighting is not available?

Yes can be, you will need permission to access any property to undertake measurements and for first floor and above windows this can be difficult from the outside. If toy look to model the existing lighting then the best assessment of the existing lighting installations should be made by a competent lighting professional of what exists where such information cannot be obtained. A base line survey is preferable.

We are constantly being asked to put obtrusive lighting
calculations to commercial properties not habited at night or open 24/7 by planners. Can you say more clearly that it is residential where control of the light spill is required?

Light nuisance is where light emitted from a premises affects the enjoyment of another within their own premises (this includes residential properties, offices, commercial buildings and the like), if the affected premises is not occupied at all hours of darkness (even mid-winter) over the whole year then the need for the calculation could be questioned – it is not residential where this applies (see definition earlier) and you must also consider spill light onto adjacent areas where work may be undertaken of public have access to, such that is  not detrimental to the task lighting provided. It is always good practice in all installations to ensure spill light and source intensity is managed and mitigated as best as possible, just to imply that as a property is not a residence that I can spill light.

When will the new publication on bats be available?
GN07/18 Bats and artificial lighting in the UK is under review and is being led by Bat Conservation Trust. Publication of the next version should be expected during 2021

Are there limits to brightness contrast suggested in GN01?
In part yes, for high mounted installations there is a requirement to adjust the E zone assessment to the next most rigorous zone, i.e., if the installation is in an E4 zone but high mast are used and the luminaires will be observed red against the night sky then GN01 advises that the assessment should be based upon E3 zone requirements. This is also an aspect for advertising and media screens discussed in PLG05.

Does the course demonstrate how to calculate intensity using software?
No, it looks ate what the design should provide and what the planners need to ask for but does not look at the specific software that does the calculations.

Where can I obtain a copy of the new Government document?
The APPG document “Ten Dark Sky Policies for the Government” is available for download at

If your front door opens directly onto the pavement, can you
still have a light, to light the area around your door?

Porch lights can still be used, following the ILP domestic security lighting document will help, essentially brighter is not better so such lighting should serve its purpose but not adversely affect the surrounding area and provided task lighting.

Is there any intent to examine and adopt the IES Luminaire classification system to produce BUG ratings for the distribution characteristics of equipment?
To be honest I am unsure, Europe (we still work as if we are in there) tends to work to CIE guidance and not that developed in the US / IES. Of course, any luminaire is only as good as it is installed and commissioned.

Will you be recommending against e.g., flood lighting where
the PIR is incorporated into the reflector?

I think you mean part of the luminaire, no not fully there are a number (few) good security luminaires on the market where the PIR and be independently angled as can the luminaire optics, however the best approach is of course a low level PIR and a higher level good optic security light. We will of course be lobbying for high street and on line retailers of such products to stock what is good practice and remove others from the market, this is in line with one of the Governments ten dark skies considerations.

How to proceed if the client requires a strategy for sensitive
species but there are no data about where these species are
located. Bats roosts?

You must call in an environmental / fauna and flora specialist to advise and in some cases surveys can only be undertaken at a defined time of the year i.e., when bats are not hibernating. The Bat Conservation Trust / ILP guidance document helps advise on this.

Does sky glow also come from the ground?
Yes there can be a reflected light content, Upward Flux Ratio, this is mentioned in GN01 and will be further clarified in the revised document. It is a very hard aspect to consider as the ground area will consist of many surfaces at a range of angles and their reflectance depend upon climatic conditions, for an example one patch of grass has been monitored, when long, cut, dry, damp, wet and covered in frost the reflectance’s ranged from 8 to 25% – really it only needs to be considered in certain circumstances and the revised GN01 will comment on this.

Will the course cover the measurement of light?
Only in an over view, photometric performance is perhaps another course the ILP may consider, a hands on course was developed and these are always best when attendees and pick up and use the instruments.

How would one go about a horrendous outdoor installation at
a private sports centre when the local authority Environmental
Team do not appear to see there is a problem?

This is a common problem in that such installations are not perhaps viewed with the concern and expertise that such complaints should be. They have a legal position that they should  investigate such concerns and the course is aimed to help planner and environmental officers understand the issues but to also stress the need to consult with competent lighting professionals. If you have no success then you may need to take matters into your own hands and employ a specialist consultant (the ILP can advise on these) and they will make a judgement and if the complaint is found valid their report will require the council to take action.

In an early ILP CPD seminar for GN/01 2020 the ILP stated that practical examples of obtrusive lighting calculations would be provided, do we know when this is going to happen? E.g., to cover GN/01 2020 Table 4, 5 & 7.

The revision of GN01 will look to advise more on the assessments to be undertaken and aspects of evidence. – due early (Jan / Feb 2021).
Will the Landscape Inst be adopting GN01 to add night-time
aspects in an LVIA?

We do not know but would hope so, GN01 in previous forms has been the ILP’s most downloaded and requested document, the majority of planner etc, reference it.

Is the base line survey incumbent on the designer or the planning authority?
The base line assessment should be undertaken by person who are competent in undertaking these, know how to use the photometers and what they are assessing, normally this would be for a lighting professional to undertake and then discuss the results with the planning authority to confirm the environmental zone etc.

How do we use Table 4 in GN01 for multiple lights in a large
car park?

Where the luminaires are view by observers as single luminaires then each is assessed on their own performance, if a group of luminaires appear as a single source to an observer then they will be defined as a single luminaire for the assessment.

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