Retrofit street lighting: the 9-point checklist

In short

A retrofit does not replace the luminaire. It adds control and a data connection to the luminaire you already own. Three questions decide whether that works: is the luminaire still photometrically appropriate, is there a usable socket on top for a node, and can the driver be dimmed digitally. Where all three answers are yes, the effort per light point stays small, because neither the column nor the cabling is touched. Where one answer is no, replacing the luminaire is usually the sounder investment.

1. Inventory and light-point data

Every project starts with a dependable asset record. For each light point you want at least the address or coordinate, the column reference, mounting height, bracket, luminaire type, wattage, year of installation and the feeder or cabinet it belongs to. Just as important is the road classification behind each street, whether it is a main road, a distributor, a residential street, a footway or cycleway, or a public square. That classification later drives groups, switching times and dimming profiles.

In practice the data tends to be scattered across a spreadsheet in the depot, a GIS layer at the utility and paper files. Reconciling it early is real work, but it repays itself, because every later quantity estimate, tender and commissioning step builds on it. Where no complete record exists, a sample survey is a sensible start, followed by systematic capture during installation.

2. Age, condition and remaining useful life

A node is an investment in the luminaire it sits on, so remaining useful life belongs at the front of the assessment. Look at gaskets and ingress protection, the state of the optic and the cover, corrosion on housing and bracket, completeness of fixings, and any pattern of faults in the maintenance log. Where a luminaire is due for replacement within a few years, the node is better fitted with the new unit, or moved across when the swap happens.

A simple traffic-light rating of the estate works well. Green means retrofit, amber means retrofit and keep under review, red means replace. That rating also produces the quantities for the two routes ENVIOTECH combines, namely retrofitting suitable luminaires and replacing unsuitable ones. The overview page street lighting modernisation sets both out.

3. LED status and photometric suitability

Retrofitting assumes the luminaire is still photometrically sound. Control does not improve a poor light distribution, it merely makes poor light dimmable. So clarify luminous flux and input power, light distribution and glare control, correlated colour temperature and the share of light spilling upwards. On earlier LED generations, efficacy and lumen depreciation matter too.

Whether a street meets its design requirements does not follow from a datasheet alone. It follows from a calculation for the actual geometry of carriageway width, spacing, mounting height and bracket. Where those records are missing, recalculating a sample of typical cross-sections is the workable route. It also gives you the evidence base for the base light level in the control concept.

4. Available socket and physical installation

A node needs somewhere to sit and an electrical connection. In practice you check whether a socket for a top-mounted module is present, whether it is accessible, whether the gasket is intact and whether the surface is flat enough. On luminaires without a socket, establish whether the manufacturer permits a retrofit and, if so, with which component. Without that approval, opening the housing can affect both the ingress protection rating and the warranty.

The mechanical and electrical basis for top-mounted nodes is described by Zhaga Book 18, while the digital driver side is described by D4i. ENVIOTECH products are compatible with Zhaga Book 18 & D4i. Keep the distinction explicit: an interface and compatibility with it are not the same thing as certification, and neither removes the need to verify the specific luminaire in your own project. The page Zhaga and D4i explains how the two specifications work together.

5. Driver, dimming and controllability

Controllability lives in the driver. Record the type and vintage, the dimming interface, the behaviour at the bottom of the dimming range, and whether the driver reports operating data digitally. Analogue dimming works, but it gives less feedback and makes fault finding harder. A digitally addressable driver allows precise curves, clean transitions and the reporting of burning hours and energy figures.

The output of this step is a list of which luminaire groups are directly controllable, which need a driver change, and which are more economically replaced outright. The node itself is described on the EnvioLux Core page, and the replacement route on the EnvioLux system luminaire page.

6. Radio conditions, network and rollout approach

Control needs communication. Check coverage across the project area, the signal at awkward spots such as underpasses, courtyards, woodland edges and industrial land, and how many light points sit together along a street. A drive survey or a short test installation at a handful of typical and deliberately difficult locations is worth doing before quantities are ordered.

The result shapes the rollout approach: the order of streets, bundling with other work such as maintenance rounds or civils, access equipment, and time windows that keep traffic disruption low. Combining installation with maintenance visits that are happening anyway brings travel costs down noticeably.

7. Control concept: schedules, groups, base light

The control concept is the part that creates the benefit. It defines which light points belong to which groups, what base level applies overnight, how dimming develops through the night, and where an increase is wanted. Start with a few well-argued profiles per road class rather than a long list of special cases, then add calendar rules for weekends, school holidays and events.

Where movement is to be detected, a sensor scenario is added: a low base level that lifts on detection and returns after a defined hold time. Such scenarios need clear rules for the level of the increase, the hold time and the handover to neighbouring luminaires. The concept is implemented and maintained in software, see the lighting management system and EnvioTerminal.

8. Data, responsibilities, commissioning and operation

Before the first installation, agree who does what. That covers associating each node with its light point at commissioning, maintaining the master data, handling faults, approving changes to dimming profiles, and which people hold which rights in the system. Also settle which operating data is recorded, how long it is retained and who it is shared with.

A short operating agreement between the authority, the operator and the service provider works well in practice, naming response times, reporting routes and named contacts. After the rollout it is then clear who brings a dark street back on, and how that gets reported.

9. Pilot, acceptance criteria and rollout decision

A pilot across a few streets makes the assumptions testable. Choose a section that mixes the typical with the awkward, so different luminaire types, different road classes and at least one location where coverage is expected to be weak. Write the acceptance criteria down beforehand, not afterwards.

• Every node is uniquely associated with a light point and visible in the system.
• Switching and dimming commands take effect reliably and traceably.
• Operating data arrives complete and plausible.
• Sensor scenarios behave as described in the concept.
• Installation time per light point and any rework are documented.

On that basis the rollout decision rests on figures from your own network rather than on assumptions. The pilot also firms up the final split between retrofit and replacement.

Retrofit or replace?

Retrofitting is usually right where the luminaire is a modern LED unit with enough remaining life, has a usable socket on top, contains a digitally dimmable driver and still suits the street photometrically. The intervention stays small and the column and cabling are left alone.

Replacement is usually right where the unit is a legacy luminaire without LED technology, has reached the end of its useful life, has no approved interface, or no longer delivers a suitable light distribution. For those light points ENVIOTECH offers the EnvioLux system luminaire, combined in the system offer with a node and EnvioTerminal. Both routes can be mixed within one project, which is the norm on a mixed estate.

What to prepare for a first assessment

• A light-point list as a spreadsheet or GIS export, as complete as it exists.
• Luminaire types with datasheets, or photos of the rating plate and the head.
• Photos of the top of the luminaire where a socket is suspected.
• Feeders, switching times and any dimming rules in use today.
• Energy consumption and maintenance effort for the past two to three years.
• Road classification per street and known special cases such as school routes.
• Planned civils or maintenance work that installation could be bundled with.

With those documents in hand, a first assessment of the estate is possible and the split between retrofit and replacement can be approximated.

Official further reading

Next step

The checklist is deliberately arranged so that the first five points can be answered from existing records and a few photos. Points six to nine take shape in conversation with planning and operations. If you would like your estate placed on that scale, a short joint review of the light-point data is the fastest way in. You are welcome to get in touch.