The Institution of Lighting Professionals (ILP) have produced a guidance note (GN01) originally published in 2001 and regularly updated. This document is a key reference document for planning applications in the UK and is generally used as the basis for assessment for lighting impacts.
This note was updated recently at the end of July 2026. One significant change is the title of the document now being ‘The Avoidance of Obtrusive Light’ rather than ‘The Reduction of Obtrusive Light’. The latest version of the guidance note is GN01/26 which supersedes GN01/21.
What Does the Guidance GN01/2026 Say?
The updated ILP guidance note:
- Provides the basis for determining an appropriate baseline for lighting through definitions for Environmental Zones
- Gives limits to how much light should be entering windows from new development
- Gives limits as to how bright new lights should be in relation to surrounding receptors
- Gives limits for upward light radiation to manage impact on the night sky
- Gives good practice design measures and mitigation options for when lighting can be a challenge.
All of the above are used by lighting practitioners to determine whether a development’s lighting will result in a significant impact and may form a significant planning constraint. There is a general principle used throughout the lighting industry that “Good lighting practice is the provision of the right light, at the right time, in the right place, controlled by the right system.”
Generally, there will always be a solution to lighting issues but this will require positive engagement with lighting designers/suppliers and environmental professionals.
What’s Changed?
The new version of the guidance retains the same general lighting principles as the previous version and the limits specified for lighting have generally not changed. As such, don’t expect that there will be a more onerous requirement for mitigating light spill from your development or that there will now be a requirement to make things even brighter.
However, there are some key differences that are worth being aware of for anyone looking at lighting assessments for planning.
Planning Requirements Checklist
There is a new example checklist which gives details on the recommended core information that Planners should request when considering any application where external lighting is being proposed.
These requirements are very specific for example including lux contours down to 0.5 lux. There is also greater emphasis on providing information as to how a lighting scheme will avoid / mitigate any potential biodiversity impacts arising from the installation or operation of the proposed lighting as well as evidence of compliance with this guidance note.
This checklist is likely to be picked up by Local Authorities when making decisions and will require a greater weight of evidence to be submitted as part of planning applications in a specific format.
What’s the Plan(ning Policy)?
While not a direct reference document for planning policy, the guidance does provide useful context for how the National Planning Policy Framework (NPPF) and Planning Practice Guidance (PPG) should be applied within a lighting context.
Of particular note is guidance’s emphasis on the “agent of change” principle. This will put greater emphasis on new developments which are going next to existing light sources to seek to mitigate the effects of light on future occupiers so they do not ‘come to a nuisance’.
Halt! Who Goes There?
One difference is that the term ‘light trespass’ is no longer used by the ILP. The phrasing around light as an environmental issue should generally be “nuisance” or “light spill”. This is because ‘trespass’ is a term used to physically encroach on land, which light cannot do.
Sky Quality Measurements are out
The previous version of the guidance suggested a typical Sky Quality Measurement (SQM) level to help inform which Environmental Zone a study site would fall into. The update acknowledges that undertaking these measurements could prove overly onerous and it is no longer recommended to use SQMs to assist in determining an Environmental Zone.
This should make the assessment of baseline easier for practitioners.
How can Lucion help?
Our in house technical team has over 15 years of experience completing detailed lighting assessments for a range of planning applications from residential and industrial developments to sports pitches.
We have a range of experience dealing with different lighting issues including:
- Lighting within protected Dark Sky landscapes
- Impact of lighting on sensitive nocturnal species (bats, badgers, etc)
- Impact of lighting from new development on surrounding sensitive receptors.
Please get in touch with [email protected] for more information.
