How to Write Solar Street Light Specifications (Checklist)

Why vague specifications fail

Three failure modes account for most of the troubled projects we see.

Non-comparable bids. When "high efficiency" carries no number, every supplier claims it. The bids arrive with different array sizes, different lumen packages, and different autonomy, and price becomes the only column a buyer can compare.

The cheap-system trap. A spec that omits autonomy days, effective projected area (EPA), or battery chemistry lets a supplier hit the price by deleting the parts nobody wrote down. The system that results performs on the drawing and fails on the road.

Disputes at handover. Acceptance criteria written as "meets industry standards" give neither side a test to run. Numbers give both sides the same test, which is why we push back whenever a spec asks for "quality construction" without a measurable definition.

There is a fourth cost that lands on the whole industry. When vague specs become normal, price becomes the only differentiator, and suppliers stop competing on engineering. The buyers who suffer are the ones who repeat the purchase, because the second tender inherits the first tender's ambiguity.

Writing principles that keep a spec honest

Three rules separate a spec that survives contact with a project from one that does not.

Write to the site, not to the ideal. Pull the local climate data, the winter sun hours, the salt-spray exposure, and the historical wind record, and put the governing values in the spec. A profile tuned to the best month of the year strands the system in the worst one.

Balance performance against cost, explicitly. A spec that demands coastal-grade corrosion protection for an inland site inflates the price for nothing; one that demands inland protection for a coastal site buys a replacement in year three. State the exposure class and let the protection match it.

Reference named standards. EN 13201 for road lighting classes, IES RP-8 for roadway lighting practice, ASCE 7 for wind loads, ASTM grades for pole steel. A spec that cites a standard number gives every bidder the same target and gives the owner an enforcement handle.

What a complete specification contains

Each section below states what we look for when that part of a spec lands on our desk.

Solar panel section

Four items make this section quotable. The number of modules, usually one or two on an integrated pole and more on a separate array structure. The cell type, monocrystalline or polycrystalline, because the choice moves both efficiency and price. The total array wattage, stated separately from the fixture wattage; conflating the two is the single most common error we correct in tender documents, and it quietly changes the energy balance by hundreds of watts. And the mounting method, because a side-mounted pole top, a wall mount, and a roof mount impose different loads, different shading constraints, and different bracket hardware. If the spec calls for a mortise-and-tenon or rod mounting on the pole side, name the bracket type and its load rating, since that joint carries the array in the worst wind the site sees.

Luminaire section

The fixture section should name the model or part number, so that two bidders quoting "120 W" are quoting the same optic. State efficacy in lumens per watt rather than total lumens alone; a high-lumen fixture with a poor distribution lights the trees instead of the road. Name the distribution pattern (batwing, rectangular, asymmetric) against the road geometry, and where the project falls under a dark-sky ordinance, state the BUG rating explicitly. BUG stands for backlight, uplight, and glare, the three spill components a lighting designer can check against a published rating in minutes. Two further references are worth writing into the spec because they make luminaire claims testable: IES LM-79 for the measured output of the complete luminaire, and IES LM-80 for the lumen maintenance of the LED package over time. A supplier who quotes LM-79 data has something to show at delivery; one who does not has a brochure.

Light levels and uniformity

Specify the area to be lit: road width, lane count, the distance from the pole to the road edge, and the surroundings that throw shade or spill. Then give the light level as a number, average maintained illuminance in lux or foot-candles, never as an equivalence to a legacy lamp. "150 W metal halide equivalent" describes nothing an installer can verify; an average of 15 lux with a 4:1 average-to-minimum ratio describes something a light meter can check at handover. If the client works to a road lighting class, name it: EN 13201 classes and the IES RP-8 practice both define measurable targets, and citing them removes an entire category of argument.

Uniformity can be reported as average-to-minimum (lower is more uniform) or minimum-to-average (higher is more uniform); these are reciprocals, so state which convention a specification uses. An average-to-minimum limit of 10:1 is only a coarse screening threshold, not a road-lighting design target or proof of compliance. The project must meet the maintained uniformity criterion for its specified lighting class and calculation method; do not substitute a generic ratio for the applicable standard. Where a project needs to see the result before steel is cut, our lighting simulation workflow turns the road geometry and a fixture's photometric file into predicted illuminance and uniformity values that can be checked against the spec.

Control system section

The controller decides when the lights fire and how deeply the battery is discharged each night, so the operating profile belongs in the spec, not in a purchase order. State whether the system runs full output from dusk to dawn or dims after a set period; whether it returns to full output before dawn; and how many hours of full output the site needs. Then let the numbers do the sizing: our controller sizing calculator takes load, system voltage, and peak sun hours and returns the charge current and the MPPT (maximum power point tracking) or PWM (pulse width modulation) class the profile requires. If the spec calls for adaptive dimming, remote monitoring, fault alarms, or data logging, say which ones, because each adds hardware and each is quoted separately. And write the winter case explicitly: a profile tuned to July sun hours will strand the system in December unless the spec says which month governs.

Battery section

Chemistry follows climate. Lithium iron phosphate (LiFePO4) packs the most energy into the smallest enclosure and tolerates deep cycling, but it should not be charged below freezing without a heated box, and sustained high ambient temperatures shorten its life. Gel and lead-acid chemistries handle temperature swings with less fuss, at the cost of weight and usable depth of discharge. Whatever the chemistry, state capacity in amp-hours at the system voltage, the enclosure's NEMA rating and material of construction, and the autonomy in days. Our rule of thumb: gel or lead-acid systems get a minimum of five days of backup; lithium systems are reliable at three. Both figures assume the array is sized for the same site, which the battery sizing calculator checks directly. A worked sanity check belongs in the spec review: a 30 W fixture running twelve hours draws roughly 360 Wh per night, and that number, divided by usable battery capacity, is where the autonomy claim either holds or collapses.

Pole and foundation section

The pole section carries the safety case, so it gets dimensions, not adjectives. Material (steel, aluminum, concrete, or fiberglass), height set by the road class and mounting height, wall thickness and diameter, base type (direct-buried or anchored), and surface treatment (powder coat, hot-dip galvanizing, or raw). Tapered and straight shafts behave differently under the same load, and the shaft geometry comparison explains which one suits a given EPA. The spec must also state the design wind speed for the site and the total effective projected area of everything mounted above the base plate; those two numbers decide whether the pole survives its first typhoon, and our wind resistance calculator runs the overturning check against ASCE 7 and Eurocode inputs. Foundations follow soil. A direct-buried base in dense sand is not the same anchor bolt count as one in rock, and the foundation calculator keeps the concrete volume and rebar honest. Finally, do not leave installation and maintenance access unwritten: a battery box that cannot be reached with a pole hook, or a fixture that cannot be lowered without a crane, turns a ten-minute service call into a road closure.

The rule we apply to every spec we quote

If a requirement cannot be measured at delivery, it is not a requirement; it is a hope. Every line we write into our own proposals carries a number, a unit, and a test method, and we ask for the same in return.

What this page does not cover

This checklist covers the component-level content of a specification. It does not size a system for a specific site, that is what the calculators above are for, and it does not replace the project-specific structural calculation an engineer of record signs. Grid-tied street lighting, high-mast systems above 30 m, and decorative poles with non-standard EPA profiles each need their own treatment. For how these parameters land on a real product, our all-in-one solar street light line shows the datasheet format we quote against.