A solar street light on a supplier listing reads 1000W, weighs 20 kg, sells for USD 90, and promises ten hours a night with five days of rainy-weather backup. Run the arithmetic once and the offer collapses: 1000W for ten hours is 10 kWh per night, and a lithium pack that size is roughly 100 kg before you add the panel that has to refill it every day.

This is the most expensive misunderstanding in the category. Inflated output claims force undersized batteries, undersized batteries produce fixtures that dim or die before midnight, and the resulting warranty argument is usually lost by the buyer on freight costs rather than on evidence.

This article explains what a wattage figure ought to mean, how to verify one in ten minutes without a laboratory, and how much power a given application actually needs.

1.Three different numbers are all called watts

The confusion is not entirely dishonest, which is what makes it durable. Three unrelated measurements share one unit, and each is defensible on its own terms.

1.1 the LED chip array maximum

Every LED chip carries an absolute maximum current rating in its datasheet. Multiply that rating by the number of chips on the board and you obtain a figure the finished fixture will never draw, because no thermal design in a pole-top housing could dissipate it. A board of two hundred chips rated at 5W each becomes a 1000W product on paper in about thirty seconds of arithmetic.

1.2 peak input power

The highest current the driver pulls for a fraction of a second at start-up. This figure is genuinely useful for selecting a fuse or sizing a connector. It is useless for deciding how long a battery will last.

1.3 sustained actual output

What the fixture draws hour after hour, night after night, across the years of its service life. Only this figure matters to an installer, because only this figure determines runtime, battery size, panel size and thermal margin. When a supplier cannot separate the three, they are not selling a specification. They are selling a number.

2.The ten-minute sanity check: watt-hours divided by load

Solar lighting is an energy balance problem, and the balance is simple enough to work out on the back of a quotation. Energy required per night equals output wattage multiplied by operating hours, divided by system efficiency. Efficiency here means round-trip losses through the controller and the pack, which for a modern MPPT system lands close to 0.95.

Apply that to a 768 Wh pack, the configuration in our 100W split-type fixture at 25.6V and 30Ah, and the result is 768 divided by 100 multiplied by 0.95, or roughly 7.3 hours at full output. That figure is modest and it is honest. Anything longer requires either a dimming profile or a larger pack, and the buyer deserves to know which one they are getting.

Pack mass above assumes roughly 100 Wh per kilogram at system level for a complete pack including management board and housing. It is an order-of-magnitude check for a quotation meeting, not a procurement specification.

The same check runs in the other direction, and it is just as revealing. If a listing claims 1000W and also quotes a 600 Wh battery, the real sustained output is around 60W. The battery is the honest part of any datasheet, because the battery carries a visible weight and a visible share of the bill of materials.

3.Four checks you can run before placing an order

None of these requires a photometric laboratory. All four can be completed in a warehouse, and together they close the gap between a brochure and a purchase order.

3.1 ask for battery capacity in watt-hours, then divide

Not 'lithium battery', and not amp-hours alone. Watt-hours. Divide the watt-hours by the claimed output and compare the answer against the stated operating hours. A 1000W fixture needing ten hours requires 10,000 Wh. If the quoted pack is 600 Wh, the arithmetic has already failed and no amount of further discussion will repair it.

3.2 ask for panel area and cell type

Panel output is proportional to area, and area is visible in any product photograph. Monocrystalline cells deliver more output per square metre than polycrystalline, which is why a monocrystalline panel of a given wattage occupies less space than a polycrystalline panel of the same rating. If the claimed panel wattage does not match the physical footprint implied by the stated cell type, one of the two numbers is decorative. Ask for the panel dimensions in millimetres and compare against the module datasheet.

3.3 ask for measured DC input current at rated voltage

A clamp meter on the input takes a minute and ends the argument. At 25.6V a genuine 100W load draws about 3.9A. At 12.8V the same load draws about 7.8A. A fixture labelled 1000W that pulls 4A at 25.6V is a 100W fixture, whatever the label and the carton say.

This check also explains why higher-power fixtures in this product class use 25.6V packs rather than 12.8V. Losses in the wiring and the switching stage rise with the square of the current, so doubling the system voltage halves the current for the same output and cuts resistive loss by roughly three quarters. It is a thermal decision, not a marketing one.

3.4 ask for lumen output, then divide by wattage

This is the cross-check that catches almost everything, because efficacy is bounded by physics rather than by imagination. High-efficiency LED modules in this product class run around 190 lm/W. Divide the claimed lumen figure by the claimed wattage and read the result.

A claim of 1000W and 20,000 lm yields 20 lm/W, which is a compact fluorescent number from the 1990s and not an LED number. Conversely, a claim of 100W and 19,000 lm yields 190 lm/W, which is at the top of what current modules deliver. If both figures are plausible, the product is likely real; if either is not, the specification is being used as decoration.

4.Wattage, lumens and optics have to agree

Efficacy tells you how efficiently electricity becomes light. Luminous intensity distribution tells you where that light goes. These are different questions and buyers routinely conflate them.

A fixture with excellent efficacy and a narrow spot optic will light a small patch brilliantly and leave the rest of the carriageway dark. A fixture with moderate efficacy and a wide asymmetric distribution will produce lower peak illuminance and far better uniformity across the road. For street lighting, uniformity and glare control usually matter more than the headline wattage, because they determine whether a driver can actually see. That question is answered by an IES file and a lighting calculation, never by a brochure.

5.How much power each application actually needs

Our range spans 3W compact floodlights to 150W road fixtures, and the split between them is driven by mounting height and required illuminance rather than by product marketing.

Two rules of thumb are worth carrying into a meeting. First, settle the mounting height before the wattage: a 150W fixture on a 4 m pole produces glare and wasted light, while a 40W fixture on a 10 m pole produces a dark road with bright patches directly beneath the head. Second, every step up in wattage is a step up in battery, panel and pole load, so the cost curve is not linear and quoting by wattage alone misleads the customer about the total.

5.Dimming is a battery decision, not a quality decision

When a supplier quotes a 100W fixture with seven hours of full-output runtime, they have three honest options: a larger battery, a shorter night, or a dimming profile. The third is standard practice across this industry and it is not a defect.

A typical profile runs at full output for the first hours after dusk, then steps down to 50 or 30 percent, often paired with passive infrared sensing that restores full output when someone approaches. The light stays on until dawn instead of dying at one o'clock, and total energy consumption fits within the pack that the customer has paid for.

It follows that dimming and occupancy sensing belong on low-traffic roads and footpaths, not on arterials. On a main road, occupancy detection creates a flickering, patchy lighting environment that is worse for traffic safety than a steady lower output, and road safety analysis generally rejects it for that reason. If a supplier offers PIR sensing on a main-road fixture as a premium feature, the right question is why the battery is not sized to hold the road at a steady level.

6.What to put in your request for quotation

A quotation request that settles these points in advance saves months of revision. Specify sustained output in watts measured at a stated ambient temperature; battery capacity in watt-hours with chemistry and expected cycle life; panel wattage, cell type and physical dimensions; controller type, whether MPPT or PWM, together with its efficiency; luminous flux, distribution type and an IES file; the dimming profile by hour after dusk; and the low-voltage cut-off point.

A supplier who answers all seven has engineering behind the product. A supplier who answers only the first has a brochure.

7.Frequently asked questions

7.1 Can a 40W fixture be upgraded to 100W by swapping the LED board?

No. The pack, controller, driver and thermal path are all sized around the original load. Doubling the LED board without matching the rest produces a fixture that overheats, drains the pack in about three hours, and voids any warranty that depended on the original configuration.

7.2 Is a higher wattage always brighter?

No. Brightness at a given point depends on luminous intensity in that direction, which depends on optics. A well-opticked 60W fixture can outperform a poorly-opticked 100W fixture on the same pole, at lower energy cost and with less glare for drivers.

7.3 Why do some suppliers quote a 1000W equivalent?

Because the word equivalent has no defined test method. It can mean equivalent to a 1000W halogen in perceived brightness at one point on the road, or equivalent to a 1000W LED array's chip rating. Neither statement can be falsified, which is precisely the attraction of the phrase.

7.4 What is a realistic battery service life?

Lithium iron phosphate cells typically retain 60 to 80 percent of original capacity after several thousand full cycles. Under daily cycling that corresponds to several years of service. Capacity fade is normal, and it is the reason a fixture that ran ten hours in its first year may run eight hours in its fourth.

7.5 Do I need a larger panel in a cloudy climate?

Yes, and it is usually the panel rather than the battery that limits recovery. Design the panel for the worst month rather than the annual average, then check how many consecutive overcast days the pack can cover. A common specification is three to five days of autonomy, and it should be agreed in writing rather than inferred from a marketing claim.

8.Sizing a project now?

Send us the road class, the pole height, the required operating hours and the worst-case overcast period for the site. Our engineering team will return a sizing sheet with sustained output, pack capacity, panel dimensions and expected runtime at the end of year one and at year five, with every assumption written down so that you can check the arithmetic yourself.