Solar Lighting Night Shift

On the Lighter Side of the Sun

By Piotr Mikus

RP-8-25, Solar Edition (Series):

Browse the series: RP-8-25, Solar Edition

Previous: Battery Budgets, Bad Optics: Why Solar Roadway Lights Get Called Harsh (RP-8-25)

(What to demand in a solar roadway lighting proposal when classification is on the table):

• Street classification and pedestrian activity level declared in writing, tied to the local jurisdiction’s designation
• Lighting criteria pulled directly from RP-8-25 Table 11-1 for that specific classification and activity combination
• Photometric results shown at the operating floor, not just full output
• Adaptive lighting narrative confirming the minimum dim level per segment does not drop below the lowest applicable criteria
• Energy budget modeled for winter worst-case: what does the system deliver after three consecutive cloudy days?
• Written justification if the proposed classification differs from what the owning jurisdiction has assigned

The classification you pick is the floor you build on. Everything above it follows from that choice.

You can submit a photometric report that passes and still be designing to the wrong street.

Most of the conversation in a solar roadway lighting proposal circles around output: watts, lumens, pole spacing, autonomy nights. Those details matter. But they all happen downstream of a decision that often gets made in a footnote: what is this street, and who uses it after dark?

In solar roadway lighting, that input is not just a label. The panel, the battery, and the energy budget are all sized to a criteria level. The criteria comes from the classification. If the classification is off, everything downstream is off with it.

What RP-8-25 is actually saying

Classification is not a suggestion. It is the starting point for every number in the design.

RP-8-25 organizes roadway lighting criteria around two inputs: street classification and pedestrian activity level. Major, collector, or local. High, medium, or low pedestrian activity. Together those two inputs point you to a row in Table 11-1, which carries the luminance target, the uniformity limits, and the glare ceiling for the design. There are nine possible combinations. The luminance difference between the top and bottom row is 4:1.

Section 11.3.1 is direct: the classification of a street for lighting purposes should best fit the descriptions in the document, and is typically defined by the jurisdiction that owns and operates the street. You are not choosing a classification because it fits the budget. You are using the one that already exists and documenting it.

The pedestrian activity layer adds precision. Section 11.3.2 defines it by peak one-hour pedestrian volume during hours of darkness. High is 100 or more. Medium is 11 to 99. Low is 10 or fewer. And when volume data is not available, the standard says to assume medium, not low. That default is not an accident.

There is a direct connection to adaptive lighting too. Section 6.10.2.2.2 says that for collector and major streets, dimming should not go below the lowest applicable criteria for the roadway classification. That floor is set by Table 11-1. If the table row was wrong, the adaptive lighting floor is wrong by exactly the same margin.

Why classification matters more in solar projects

Solar lighting is sized to a criteria. Get the criteria right and the whole system is traceable from street designation to hardware on the pole.

In a well-engineered solar roadway lighting system, the classification feeds the criteria, the criteria feeds the energy load, the energy load feeds the battery and panel sizing. Every step is connected. That traceability is exactly what makes a properly specified solar installation defensible when someone asks questions at year two.

It also means the maintained criteria apply year-round, not just at summer commissioning. A system that delivers its luminance target in August needs to deliver it in February too. The energy budget needs to be modeled for worst-case, not average. Classification compliance is not a seasonal condition.

When the classification is right, the system has the margin it needs. The dimming floor is where it should be. And the owner gets what they paid for every night of the year.

Where the disconnect usually lives

Classification questions come up most often when the project documentation and the field reality are two different things.

A collector street that carries bus service and retail access gets described as local. A corridor with consistent evening foot traffic gets assigned low activity because the only count available was from a mid-January morning. An intersection with documented pedestrian conflict gets the same activity assumption as the quiet midblock stretch on either side of it.

None of these are outright fabrications. They are judgment calls made with incomplete inputs and no documentation trail. The problem is that those calls run through the entire design. The luminance target, the uniformity requirement, the adaptive floor, and the energy budget all flow from that one input at the top.

The fix is not complicated. It is documentation. Street classification referenced to the jurisdiction’s own records. Activity level tied to an actual count or a declared assumption with a stated basis. Criteria row identified. Results shown at the operating floor, not just at full output.

What to Require in a Specification (especially for solar)

If the classification is not documented, it was not decided. It was assumed.

Keep it vendor-neutral and enforceable:

• Street classification and pedestrian activity level stated in writing, referenced to the jurisdiction’s functional classification system
• Basis for the activity level documented: volume count, land use, or density data. If medium is assumed per RP-8-25 default, state that explicitly
• Table 11-1 criteria row identified for each segment, with the luminance target, uniformity limits, and veiling luminance ratio stated
• Photometric results at full output and at the minimum operating level, both compared against the applicable criteria row
• Adaptive lighting narrative showing the minimum dim level per segment stays above the lowest applicable criteria floor for the declared classification
• Energy budget modeled for winter worst-case with maintained luminance confirmed above the criteria floor under low state-of-charge conditions
• Written justification if the proposed classification diverges from what the owning jurisdiction has assigned

If you only take one thing from this post, make it this: show me the criteria row, and show me the system still meets it at the operating floor.

Three Questions That Expose Classification Problems

These questions are polite. The answers are not always comfortable.

What is the street classification and pedestrian activity level used for this design, and where is that documented against the jurisdiction’s functional classification system?

If the answer is a footnote in the photometric report with no reference to local documentation, the classification was chosen, not verified.

What Table 11-1 criteria row was applied, and what does the photometric submission show at the minimum operating level against that row?

Full-output compliance is easy. Operating-floor compliance is where actual performance lives. If results are only shown at full output, the dimmed state was never verified against criteria.

What does the system deliver in February, after three consecutive cloudy days, at 2 a.m.?

If the energy budget was not modeled for winter worst-case, the classification compliance claim has never been verified for the conditions that matter most.

Closing Thought

Solar roadway lighting can be excellent. But if the classification was chosen to fit the hardware rather than to match the street, the system was specified to pass, not to perform.

Make classification a documented decision, not a convenient assumption.

Sources and Where to Verify

• ANSI/IES RP-8-25 (2025), Part 2: Section 11.3.1 (street classification for lighting purposes, relationship to jurisdictional functional classification)
• ANSI/IES RP-8-25 (2025), Part 2: Section 11.3.2 (pedestrian activity classification, High/Medium/Low definitions, default assumption when volume data is unavailable)
• ANSI/IES RP-8-25 (2025), Part 2: Table 11-1 (Design Criteria for Streets, Bicycle Lanes, and Shared Streets)
• ANSI/IES RP-8-25 (2025), Part 1: Section 6.10.2.2.2 (adaptive lighting floor for collector and arterial streets)
• ANSI/IES RP-8-25 (2025), Part 2: Section 11.6.4 (maintained values and field verification guidance)

Piotr Mikus is a roadway lighting designer and specifier focused on solar powered street lighting and controls.

Quick FAQ

Can I use a lower classification than what the jurisdiction assigned if I think activity is low?

No. RP-8-25 ties the lighting classification to the jurisdiction’s designation. If you deviate from it, you need written justification and owner acceptance. The activity level is a separate judgment call, but the street type is not yours to reassign.

What activity level should I use when I have no count data?

RP-8-25 Section 11.3.2 says assume medium unless land use and density clearly support high or low. If a proposal defaults to low without documented rationale, that is a judgment call that deserves a question.

Do the Table 11-1 criteria apply at the dimmed operating level?

Yes. The maintained criteria apply to the condition the system actually operates in, not just peak output. The minimum dim level must still satisfy the lowest applicable criteria row for the street classification. That is the floor the design is accountable to every night.

Also in RP-8-25, Solar Edition: Battery Budgets, Bad Optics: Why Solar Roadway Lights Get Called Harsh (RP-8-25)