Neighbourhood Lighting Audit: Map Your Street's Light Pollution in One Evening

One evening walk, a notepad, and honest attention — that is all it takes to document the rogue floodlights, tilted streetlamps, and blazing signboards that are quietly turning your neighbourhood sky from black to orange

It started with a failed photograph. A member of a Bengaluru astronomy club drove two hours to a supposedly dark site beyond Kanakapura, set up her camera on a tripod, and shot a forty-second exposure toward the Scorpius star clouds. The result was a muddy amber gradient across the entire left side of the frame — not the soft, even skyglow of a merely light-polluted sky, but a directed shaft of brightness, as if someone had aimed a spotlight at the horizon. Back home the next morning, she pulled up a map and traced the bearing: it pointed straight back through her own neighbourhood, past a newly opened shopping complex on the main road, and into the dense residential grid beyond.

The dark-sky site was fine. Her neighbourhood was the problem — and she had never actually looked at it.

Most of us who care about light pollution think about it at the scale of cities. Delhi versus Bengaluru. Suburbs versus city centres. Bortle 6 versus Bortle 4. But light pollution is not a smooth, uniform field radiating equally from every building. It is the sum of thousands of individual fixtures: a sodium streetlamp angled fifteen degrees past vertical, a petrol station canopy blazing at 50,000 lumens with no downward shielding, a housing-society gate with four ornamental uplighters pointing directly at the sky, a vegetable-market signboard left running until 3 AM.

Each one contributes a small, specific, mappable increment of brightness to your local sky — and each one is, in principle, fixable.

This post will walk you through a single evening's neighbourhood lighting audit: how to plan it, what to record, what the numbers mean, how to turn your notes into a usable map, and how to connect that map to SkyQI's dataset. By the time you finish reading, you will know enough to step outside tonight and begin.

Why a Neighbourhood Audit Is Different From a Sky Reading

When you upload a zenith photograph to SkyQI and receive a Bortle class in return, you are measuring the sky's integrated brightness — the sum total of every photon arriving at your camera from every direction. That number is genuinely useful, but it tells you nothing about which fixture is responsible for which portion of that glow, or which direction on your horizon is worst.

A neighbourhood lighting audit works at a finer grain. Instead of measuring the sky, you measure the sources that create it — and you do so on the ground, during a single evening walk, with tools you almost certainly already own.

The distinction matters for two reasons.

First, it determines what is actionable. An SQM reading of 18.5 mag/arcsec² tells you that your sky is approximately Bortle 6 — suburban, with a strong grey-orange cast and no visible Milky Way. It does not tell you that the primary contributor is the three unshielded metal-halide floodlights on the society boundary wall twenty metres north of your rooftop, which could be replaced with fully shielded LED fittings for a few thousand rupees per fixture.

Second, it generates data at a resolution that aggregate sky-brightness maps cannot reach. Satellite-based measurements like VIIRS-DNB, which inform global light pollution maps, have a pixel resolution of roughly 750 metres. Your neighbourhood audit can resolve individual fixtures. The two scales are complementary, not competing.

A useful way to think about it: SkyQI gives you the fever chart; the lighting audit gives you the diagnosis.

What You Need Before You Step Outside

The audit requires almost no equipment. Here is what is worth preparing:

Essential

• A notepad and pen, or a voice-memo app running on your phone. You will be recording fixture positions, fixture types, shielding status, and estimated light direction. Paper survives a dropped phone; voice notes are faster. Use whichever suits your pace.
• A smartphone with GPS-enabled maps. Google Maps, Apple Maps, or any app that lets you drop a named pin will do. You are building a spatial record, not just a list.
• A compass, or a phone compass app. You need to record bearing, not just "to the right of the water tank."
• A watch, or your phone's clock. Record the time of each observation — night-time lighting changes between, say, 8 PM and 11 PM as shops close.

Useful but optional

• A phone camera with a wide-angle mode, set to the same manual exposure and ISO for every shot. Consistency matters more than absolute quality; you are making comparisons, not art.
• A sky-quality measurement app (there are several Android and iOS options that use the phone camera to approximate SQM readings). These are less accurate than a dedicated Sky Quality Meter, but they give directional readings — point your phone at a specific bright zone in the sky and record the number. Do this before, during, and after passing major sources to see their contribution.
• A copy of your municipality's street-lighting maintenance contact or the online grievance portal URL. Some people discover during their audit that they are ready to file a report that same night.

What you do not need

Expensive equipment. A light meter would be nice; you almost certainly do not own one and do not need to buy one for a first audit. The goal of a neighbourhood walk is not photometric precision — it is a structured, spatially indexed catalogue of sources. That catalogue is what SkyQI and your local residents' association can both use.

Designing the Walk: Route, Timing, and Conditions

The quality of your audit depends on how you plan the route as much as on what you observe along the way.

Timing

Conduct the walk between 8:30 PM and 11 PM IST. Earlier than this, twilight may still be contributing to sky brightness; later than this, many commercial sources switch off, and you will under-count. If you suspect a specific late-night contributor — a petrol pump, a 24-hour shop, a hospital — note it separately and re-check after midnight.

Choose a night within a few days of new moon if possible, so that natural lunar skyglow does not confuse your directional readings. A clear, calm night is best: wind affects whether fixture light spreads or concentrates, and clouds act as a reflective ceiling that makes the overall sky brighter but makes directional attribution harder.

Avoiding rain-washed conditions is particularly relevant in India: a night three or four days after heavy rain will show artificially low sky brightness because the monsoon or pre-monsoon shower has scrubbed the atmosphere clean. Useful for a sky-quality reading; misleading for an audit, because the fixtures are still there and will matter again tomorrow.

Route design

Walk a grid, not a loop. A loop around the perimeter of your neighbourhood will miss interior sources; a loose grid of parallel streets ensures coverage. In a typical urban residential colony of, say, 500 metres by 700 metres, three parallel passes spaced 150 metres apart gives adequate coverage in about ninety minutes at a comfortable walking pace.

Mark your route on a map before you leave. Drop a start-pin when you begin. Drop a pin at every significant observation. When you return, your map already contains a spatial record; the notepad provides the detail.

Safety

Walk with a companion if your neighbourhood is poorly lit (which, if you are doing a lighting audit, it probably is in some sections). Wear light-coloured clothing so vehicles can see you. Carry a small torch or headlamp — but use a red-light mode or a dim setting, because you want your eyes at least partially dark-adapted for the directional sky assessments.

The Observation Checklist: What to Record at Each Source

Every significant light fixture you encounter deserves a brief standardised entry. The following checklist takes about forty-five seconds per fixture once you are in the rhythm of it.

1. Location Drop a GPS pin on the map. Verbal description for the notepad: "Southeast corner of Society Gate 2 on MG Road" is sufficient backup if the pin fails.

2. Fixture type Choose one: streetlamp, floodlight, signboard (backlit / frontlit / LED strip), decorative uplighter, security light, commercial facade, petrol pump / forecourt, construction site, temple or religious structure, other.

3. Light source technology (approximate)

• Orange-yellow glow: old high-pressure sodium (HPS). Common on older BBMP, MCGM, or GHMC streetlamps. Relatively narrow-spectrum, scatters less in blue-sensitive eyes.
• Cool white: metal halide or modern LED. Broader spectrum, higher blue content, scatters more in atmosphere and biological tissue.
• Warm white: LED with lower colour temperature (below 3,000 K). Better than cool white, though still relevant.
• Green-tinted: some older mercury vapour lamps still in service in older Indian neighbourhoods.

4. Shielding status This is the single most important variable in the audit. Record one of three states:

5. Direction of primary emission If the fixture is aimed upward or angled above horizontal, record the bearing it faces. A streetlamp that has been knocked off its horizontal mount by a collision and now angles at roughly 20° above level sends a large fraction of its output directly skyward.

6. Estimated wattage / intensity You cannot measure this without equipment, but you can estimate:

• Dim: about equivalent to a 60 W incandescent. You notice it but can look at it comfortably.
• Medium: about equivalent to a 150 W floodlight. Visibly bright from 50 metres.
• Bright: clearly too bright for its context. Uncomfortable to look at directly. Likely 400 W or above in equivalent output, or a multi-fixture array.

7. Operating schedule Is it on a timer? Does it appear to run all night? Is it motion-activated? A streetlamp that runs from dusk to 6 AM at full power contributes far more to cumulative sky brightness than one that dims to 30% after midnight — a feature increasingly common in newer municipal LED installations.

8. Sky brightness estimate in that direction Point your phone camera (or your phone's SQM app) at the sky directly above or just above the fixture. Note the relative brightness compared to the zenith. Even a subjective "much brighter / slightly brighter / same" is useful when you are correlating sources with sky directions later.

Categorising What You Find: A Rogue's Gallery of Common Offenders

Not all fixtures contribute equally. After doing dozens of neighbourhood audits across Indian cities, a few types turn up repeatedly as the most damaging contributors relative to their actual functional need.

The angled streetlamp Original Indian street-lighting installations often used sodium vapour lamps with a slightly upward tilt, since the assumption was that higher mounting angles improved road coverage. Many of these have never been reoriented after being struck by vehicles or shifted during road work. A 150 W sodium lamp angled 15° above horizontal sends a meaningful fraction of its output directly skyward. There is no functional justification for this — the road below is lit equally well by a downward-aimed fixture — and it is almost always fixable by a maintenance request to the local municipal body.

The forecourt array Petrol stations in India, and increasingly large format retail stores, use multi-fixture flat-panel or drop-lens LED canopies that are optimised for maximum vertical-surface illumination. A single forecourt canopy can produce upward spill equivalent to dozens of residential streetlamps. The fixtures are often rated at 200–400 W equivalent per panel and are left running through the night regardless of whether the forecourt is occupied.

The decorative uplighter Housing society gates, temple entrances, heritage buildings, and hotel facades frequently use ground-mounted or low-wall-mounted uplighters that aim directly at the sky or at a vertical surface from which light scatters upward. A row of six 50 W uplighters on a gate pillar sends the majority of their output skyward. They illuminate nothing useful — the gate is lit from signage and streetlamps — and serve purely an aesthetic function that could be achieved with fully shielded fittings at a fraction of the upward emission.

The unsynchronised commercial signboard LED strip signboards along commercial streets in Indian cities are often left running through the night on simple on-off timers set to a full-night cycle. A large backlit flex board or LED matrix sign running at full brightness at 2 AM contributes significant horizontal and upward scatter, with zero commercial benefit since the businesses are closed.

The construction site flood Temporary floodlights on construction sites are almost universally unshielded, often angled to illuminate vertical surfaces, and frequently left running all night for security. They are a transient but intense source of local skyglow, and because construction in Indian cities rarely stops for more than a few months, the neighbourhood effect is semi-permanent in many areas.

Building the Map: From Notes to a Usable Spatial Record

Once you return from the walk, you have a set of GPS pins and a set of notepad entries. Combining them into a usable map takes about thirty minutes.

Option 1: Google My Maps Create a new map in Google My Maps (maps.google.com/mymaps). Import your dropped pins if your phone saves them as a KML or GPX file, or simply re-enter them manually. For each pin, fill in the description field with your fixture-type, shielding-status, and estimated-intensity notes. Colour-code pins by severity: red for unshielded high-intensity, yellow for partially shielded or medium-intensity, green for fully shielded or low-intensity. Share the map with your housing society committee, RWA, or local astronomy club.

Option 2: A hand-drawn sketch map If you are not comfortable with digital mapping tools, a sketch map on graph paper scaled to your neighbourhood serves the same purpose. Mark streets, label key landmarks (the water tank, the society gate, the main road junction), and plot each fixture as a symbol with a number corresponding to your notepad's numbered entries. This is slower to share but often more legible in a meeting with a municipal representative than a smartphone screen.

Option 3: OpenStreetMap notes OpenStreetMap allows public notes on the map that anyone can read and contribute to. This makes your audit immediately available to other citizen-science contributors in your area and to urban-planning researchers who use OSM data. It is more public than you may want for your preliminary observations, but for final, confirmed data it is an excellent option.

Regardless of the tool, the map is the deliverable. It is what you can show at a residents' association meeting, send to the municipal ward office, or submit as context alongside your SkyQI readings.

What the Numbers Mean: Estimating Your Audit's Sky-Brightness Impact

You cannot calculate a precise SQM contribution from a fixture without radiometric equipment. But you can make useful order-of-magnitude estimates from first principles, and those estimates are often persuasive enough to motivate action.

The key relationship is this: the upward luminous flux from a fixture, combined with atmospheric scattering, determines how much it brightens the sky above it. The relevant parameter is called the upward light output ratio (ULOR) — the fraction of a fixture's total output that exits above the horizontal plane.

Approximate ULORs by shielding type:

A residential colony of 200 households with an average of three exterior fixtures each — gates, security lights, balcony lamps — and a ULOR averaging 20% sends roughly 240,000 W × 0.20 = 48,000 W (48 kW) skyward if the average fixture is 200 W equivalent and unshielded. Replace the same fixtures with full-cutoff alternatives and that figure drops to under 2,400 W. The sky above the colony would measurably darken within days.

This is not a theoretical exercise. The town of Flagstaff, Arizona — famously the world's first International Dark Sky City — reduced its skyglow measurably after mandating full-cutoff streetlamps across the municipality. Closer to home, Hanle's IAO has worked with the Ladakh administration on a dark-sky reserve that includes lighting standards for villages within the reserve's boundary. The physics work the same whether the colony is in Ladakh or in Koramangala.

What This Means for SkyQI Readings

Your lighting audit and your SkyQI measurements are, ideally, taken at the same time from the same location, and they talk to each other in a specific way.

When you upload a zenith photograph to SkyQI, the platform returns an SQM value and a Bortle class. If you have also conducted a lighting audit on the same night, you now have both the integrated measurement and the source catalogue. That combination is far more valuable than either piece alone.

Consider: SkyQI's map may show your neighbourhood at a uniform Bortle 6. But your audit reveals that within that Bortle 6 neighbourhood, there are three point sources — the petrol station forecourt, the housing society gate uplighters, and an unshielded construction floodlight — that are responsible for most of the directional sky brightness, particularly toward the south. The rest of the neighbourhood's contribution is moderate and comes from well-aimed but unshielded streetlamps that could be partially mitigated.

Upload that context as a comment on your SkyQI reading. The platform's ability to track change over time is one of its core functions: if the petrol station replaces its forecourt canopy with downward-shielded LED panels in six months, a follow-up SkyQI reading from the same location should show a measurable improvement in the southern quadrant of the sky. Your audit is the baseline that makes that change detectable.

If you conduct audits at multiple locations across your city — different neighbourhoods, different Bortle classes — the aggregate picture begins to show which types of land use produce the worst skyglow, which municipal wards have the worst fixture maintenance, and where targeted advocacy would produce the largest sky-quality improvement per unit of effort. That is citizen science operating at its most useful.

Making the Audit Count: Who to Send Your Results To

Conducting an audit and filing it away changes nothing. The audit's value is in who you share it with.

Your Residents' Welfare Association (RWA) or Housing Society Committee Most Indian urban residential societies have a maintenance committee with the authority to change or redirect exterior fixtures within their property boundary. Decorative uplighters, gate floodlights, and building facade lighting are all within their remit. A one-page summary with a simple colour-coded map is usually sufficient to get at least a conversation started. Frame it in terms of electricity savings as well as sky quality — full-cutoff fixtures direct light downward where it is needed, reducing the wattage required to achieve the same illumination level. Lower electricity bills are a more universal motivation than darker skies.

Your Municipal Ward Office Streetlamps on public roads are owned and maintained by the local municipal body — BBMP in Bengaluru, MCGM in Mumbai, MCD in Delhi, GHMC in Hyderabad, and their equivalents elsewhere. Most municipal bodies have an online complaint portal for streetlamp maintenance. A report identifying specific lamp post numbers (usually stamped on the pole), with GPS coordinates and a description of the tilting or shielding defect, is something a maintenance team can act on. Not all will respond promptly, but the reports are logged, and persistent follow-up across multiple residents is more effective than a single complaint.

Local Astronomy Clubs Every major Indian city has at least one active amateur astronomy club — the Astronomical Society of India has member clubs in most metros, and informal groups exist in many smaller cities. Sharing your audit data with these groups adds it to a cumulative local record and sometimes prompts collective action that an individual resident cannot achieve alone.

The SkyQI Platform Upload your sky readings from before and after any fixture change you succeed in getting made. Tag the location accurately. Add notes describing what changed. Over time, the platform's dataset will reflect real, ground-level improvements in sky quality driven by exactly this kind of neighbourhood-level work.

A Final Reframe

It is tempting to feel that light pollution is a problem too large for a single evening walk to address. Delhi's skyglow is visible from space. Mumbai's coastal glow can be seen from an aeroplane at 30,000 feet. The VIIRS-DNB satellite data shows India's entire Indo-Gangetic plain as a nearly unbroken sheet of artificial light.

But the sheet is made of individual fixtures. Each one was installed by a specific person, is maintained by a specific organisation, and can be changed by a specific decision. The aggregate problem is large because the number of individual contributors is large — and that means the aggregate problem is also reducible one fixture at a time.

The Vedic astronomers who compiled the Surya Siddhanta observed from a sky undimmed by anything except the moon and the natural atmosphere. They could not have imagined that the greatest challenge to their successors' view of the sky would come not from clouds or monsoon but from the collective light of a billion lamps. But they would have recognised the principle: precise observation requires knowing your conditions, characterising your errors, and working methodically to reduce them.

Your neighbourhood audit is that work, applied to 2026.

Step outside tonight. Note what is illuminated that does not need to be. Note what faces upward that should face down. Drop a pin. Write it down. Upload a sky reading. Build the map, one street at a time, and let the data do what data does best: make the invisible visible, and the fixable undeniable.