FLASH CORDON?

At the Centenary Lighting Summit in June I had the opportunity to share my thoughts on flashing lights, and whether they are an unconsidered nuisance. In this article, I intend to put these thoughts to paper – and set out my perspective on how we can begin to address this gap.

The existing picture for obtrusive light is set out well in ILP Guidance Note 1 – The Reduction of Obtrusive Light.

It outlines the four key pillars of obtrusive light (light intrusion, luminous intensity, skyglow, and building façade luminance) and outlines how to mitigate them.

What I’d like us to consider is if there is a fifth pillar, one that isn’t fully fleshed out yet. That pillar is frequency. I don’t believe there is enough in the current guidance to address specifically the frequency with which lighting is switched on and off.

Now, I’m not talking about flicker here, or pulse width modulation. Rather, I’m specifically talking about when lighting is switched on and off or is variable because of some form of malfunction, intervening feature, or inalienable aspect of the light source. I’m thinking where the frequency of this switch is below 3hz, maybe with a focus on the 3hz-0.1hz range.

Why has this come up as an issue for me? Well, I recently had the pleasure of staying at my parents’ house, in my childhood bedroom.

While, obviously, it was lovely to see them, in other respects this was a nightmarish experience. This was partially because they’d completely redecorated and erased all evidence of my existence but, more seriously, because of a new floodlight that was adorning the neighbour’s garage, behind the garden fence.

It’s a PIR floodlight, which is activated by passing users – and also the medium-sized buddleia bush that sways in front of it throughout the night!

The result was an intermittent light, switching on and off, pointed towards the window where I was sleeping. In a room alas with no blackout curtains.

Being the lighting engineer that I am, I returned the following evening with a lux meter, to measure what the illuminance was on to that window. I came out with 1.9x lux; just shy of the 2-lux limit for an E3 environmental zone.

So my question is: should this be classified as a nuisance? After a disturbed night, it certainly felt as if it should. However, digging through the available standards and guidance I couldn’t find a clear steer on how to approach this.

WHAT DOES THE LIGHTING GUIDANCE SAY?

The first port of call for these types of queries is always ILP GN01 and CIE150. I drew a blank looking through these, but I did find some potentially helpful references in ILP GN09 and ILP PLG05 [2]. These were as follows:

  • GN09 – in reference to porch lighting. ‘These units can be fitted with a movement detector if required and are generally mounted lower and are therefore less susceptible to nuisance switching on/off and complaints from Neighbours.’
  • PLG05 – In reference to digital displays. ‘Static images shall not change more frequently than every 10 seconds unless approved to do so by the Local Planning Authority.’
  • PLG05 – again in reference to digital displays. ‘Nuisance could… be prejudicial to health due to disturbing effects relating to the images being displayed by both day and night, especially when these are animated or video in nature.’

What these references offer us is an acknowledgement of the potentially disturbing nature of variable lighting.

Especially in the case of PLG05, it gives us a reference point of 10 seconds for the changing of static images – which is a helpful benchmark for establishing what could be potentially considered a nuisance.

WHAT DOES WESTMINSTER HAVE TO SAY ABOUT THIS?

The legislation and case law around this subject is quite layered – with each document referring to the next one down the line. Peeling back those layers, we do find some useful information.

The first stop is the National Planning Policy Framework 2019 (the NPPF). This states that planning policies should be limiting the impact of light pollution from artificial light on local amenity. No specific lighting guidance, but good to include. So, next, we go to the Clean Neighbourhoods and Environment Act 2005 (the CNEA).

The CNEA amends the Environmental Protection Act 1990 (the EPA) to extend the statutory nuisance regime to include light nuisance. The EPA, in turn, then sets out that this means: ‘Artificial light emitted from premises so as to be prejudicial to health or a nuisance.’

We’re getting somewhere here, but it still doesn’t define what constitutes a nuisance; that’s up to the local planning officer.

So, next, we go to case law. Except there is no lighting case law. There is only noise case law. So, we have to use that instead.

This, clearly however, isn’t ideal, even if noise case law in fact can get us some of the way. It’s not always going to be relevant.

I’d argue that it’s easier to shut out light pollution than it is noise pollution; the environmental zone considerations don’t transfer very well, noise complaints are more likely to come from directly adjacent residents than residents with a view of your lighting – the list goes on. I think noise case law gets us closer, but it isn’t the ideal situation. It’d be lovely if we had some guidance.

The last thing that is worth mentioning for background is the recent House of Lords inquiry and report into noise and light pollution. By which I mean the House of Lords Science and Technology Committee’s report into the impact of noise and light pollution on human health, published July 2023, which of course the ILP fed into.

Even if the then government’s response to it was lacklustre, this was a good deep dive into the existing legal framework, and the gaps in that framework in terms of legislation or information needed.

For me, the most pertinent points to come out of this were the recommendations that the government should:

  • commission research to establish how light intensity, wavelength, duration, time of exposure, light history and age affect the circadian system;
  • carry out research to establish he level of risk from glare, flicker, and dazzle, for example in night-time driving; and
  • issue a light policy statement for England that detailed the government’s policy on minimising light pollution and the roles it expected different departments to play, and that said light statement and planning guidance should incorporate up-to-date guidance from organisations such as the ILP, among others.

WHAT KINDS OF SOURCES ARE THE PROBLEM?

Again, it is important here to draw a distinction between ‘flashing’ light or what we could call ‘nuisance switching’ and flicker, specifically the kind of flicker that affects people with photosensitive epilepsy.

To my mind, the legal framework in place here is very clear. People with epilepsy can have a seizure triggered by flashes between 3-30hz and, in some people, up to 60hz.

If you point a light flashing at 20hz towards someone’s window then that, clearly, has the potential to be prejudicial to health – and a planning officer would have a very easy decision to make.

The question to my mind then becomes, what kind of frequencies and sources am I talking about when I say flashing lights?

Really, I’m talking about sources that are less than 3Hz, potentially with a focus on the 3hz to 0.1hz range. Not enough to cause an epileptic response, far too low to be considered ‘flicker’ – just enough to annoy someone.

There are several sources of lighting, some of them becoming more prevalent, that flash in this band of frequencies. These include:

  • Belisha beacons. These are often a source of complaints in urban environments.
  • Vehicle headlights. As Allan Howard highlighted in last month’s edition of Lighting Journal, this is something we’re getting asked to consider more and more recently.
  • Driver failures. By this, I mean the distinctive flash of a failed LED driver.
  • Intervening foliage. This is where foliage moves in front of a light to create a strobing effect.
  • PIR lighting. As I experienced at my parents’ house, this is flashing or intermittent floodlights, porchlights and the like, the list goes on.

PIRs, especially, have come up with my work a lot more recently. I spoke to my colleague Rob Fuller, whose neighbour’s PIR-activated floodlight shines into his front window – and he told me the floodlight even comes on when he stands up from the sofa!

WHAT CAN BE DONE?

I should start with a statement of intent here: I believe, based on what I’ve shown, that this subject passes the tests for requiring additional guidance.

First, there are relevant cases where this kind of light can occur. Secondly, there is, to my mind, currently a gap in available information on what to do if this occurs.

Lastly, there is the potential for negative effects to occur if lighting is applied incorrectly and cannot be effectively challenged due to gaps in guidance.

Where and how could this guidance develop? First, we could look at developing a new professional lighting guide or guidance note to cover the effects of frequency on potentially sensitive receptors, in the same vein the existing PLGs. In truth, this seems excessive to me, but I mention it for completeness.

Secondly, we could perhaps look to update GN01 to include frequency as an element, identifying the frequency of light as an obtrusive light component or a worsening characteristic of other obtrusive light components.

Lastly (and I won’t be offended!) it might be that the consensus is that this simply isn’t considered enough of a problem to require separate guidance.

Or, more realistically, this is the kind of problem that simply requires a qualified lighting professional to use their professional judgement. I’d be interested to hear members’ views or feedback.

Toby Penter BA (Hons), IEng, MILP is senior engineer | Lighting & Energy Solutions at WSP. Members who wish to discuss Toby’s ideas can get in touch with him at Toby.Penter@wsp.com

  • This is an abridged version of the article that appears in the October edition of Lighting Journal. Click on the link to the edition to read the full article.

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