Most wattage mistakes happen before a quotation is requested. A contractor picks 60W because the last project used 60W, then discovers that this road is wider, the poles are taller, or the rainy season is longer. The result is either dark patches or an oversized system that wastes panel and battery budget.

The Five Inputs

1. Road width and traffic type. A motorcycle lane and a truck route need different distributions at the same width.
2. Mounting height. Higher poles spread light further but reduce illuminance on the surface.
3. Pole spacing. Evenness is a geometry problem before it is a wattage problem.
4. Sunshine hours and rainy-season length. These set the battery autonomy requirement.
5. Required nightly runtime and dimming profile. Full brightness all night is a different system from dimmed-plus-motion.

The Selection Table

Why Spacing Comes Before Wattage

Doubling wattage on the same spacing creates a bright pool under each pole and dark gaps between them. Reducing spacing by five metres usually produces more even light for less money than adding 30W. This is the single most useful rule in road lighting, and the one most often ignored in quotations.

The Autonomy Calculation

Nightly energy consumption equals power multiplied by runtime, adjusted for the dimming profile. Battery capacity must cover that consumption across the longest expected run of low-sun days, with a margin for ageing. A system sized on the annual average will fail in the worst week, which is the only week anyone remembers.

What to Send a Supplier

• Road width and length, with a simple sketch if possible.
• Planned or existing pole height and diameter.
• Average sunshine hours and rainy-season length.
• Required lighting hours and whether dimming is acceptable.
• Any tender illuminance class the project must meet.

A Common Mistake

Contractors often add wattage to fix a uniformity problem. The result is a brighter pool under each pole and darker gaps between them, at a higher cost. If the complaint is “dark patches", the first fix is spacing or mounting height, not power. If the complaint is “not bright enough overall", then wattage is the right lever.

Diagnosing the complaint correctly saves more money than any negotiation on unit price.

With those five inputs, a supplier can produce a layout and a power list instead of a guess. If a quotation arrives without a layout, it is a price, not a design.