Lighting Simulation for Solar Street Lights
-- What It Decides
Lighting Simulation for Solar Street Lights: What It Decides
Lighting simulation earns its keep by catching two expensive mistakes before installation: under-lighting that fails inspection, and over-lighting that pays for twice the panels and batteries the site needs. In our factory, every quotation starts with the photometric file, not the price list. The model decides pole count, luminaire wattage, aiming, and — through the energy balance — the size of the PV array and battery. Here is what it settles, and with what numbers.
What the model actually simulates
A lighting simulation takes the luminaire's photometric file (the IES file every serious manufacturer publishes), places it at the real mounting height and spacing, and computes illuminance across the ground plane. The outputs we read: average lux, the average-to-minimum ratio, and where the hot spots and dark bands land. That is the whole job. The tool does not decide anything by itself; it settles arguments with arithmetic.
Brightness targets by area type
Each area type carries its own target, and the simulation checks the layout against the right one:
| Area type | Typical design target (horizontal average) | Uniformity (avg:min) | Default color temperature |
|---|---|---|---|
| Parking lots | 5–10 lux | 4:1 or better | 4000 K |
| Residential streets | 5–15 lux | 4:1 or better | 4000 K |
| Arterial / main roads | 15–30 lux | 4:1 or better | 4000 K |
| Parks and trails | 2–5 lux | Not critical | 3000 K |
These ranges reflect common industry practice. The governing code for your project — EN 13201, the IES RP-8 and RP-20 families, or a local standard — is the final word, and we check the design against it before anything ships. For parking lots we also check vertical illuminance at face height: roughly 2–4 lux at 1.5 m is the common security-camera benchmark, and it is the number that matters when someone reviews footage at 2 a.m.
A worked example from our quoting desk: a 1,800 m² lot at a 5-lux target needs about 9,000 lumens delivered to the ground. With a typical utilization factor near 0.6, that means roughly 15,000 lumens of installed output, which two 8 m poles with 100 W luminaires cover comfortably. The buyer had budgeted six poles from an eyeball estimate; the model cut four of them and the energy bill with them.
Color temperature: what changes besides mood
The standard split — 4000–5000 K for busy streets, 2700–3500 K for parks and leisure areas — is sound, and we keep it. Two engineering facts sit behind it:
- Warm light costs watts. LED efficacy drops as color temperature drops, typically by 10–20% moving from 5000 K to 3000 K. On a solar system, that penalty lands directly on panel and battery sizing.
- Cameras need color. Below 3000 K, color rendering degrades enough to hurt identification on security footage. For security-driven sites we do not go warm.
Our defaults: 4000 K for roads and parking, 3000 K for parks where dark-sky concerns dominate. Pick color temperature before the simulation, not after — it changes the energy result.
Aiming, tilt, and spacing
Mounting height sets the spacing budget. On roads, the classic rule of thumb is a spacing of three to four times the mounting height, and the simulation confirms or breaks it before the poles are ordered. Tilt matters less than people assume: 15° is the road-lighting default, and the model shows where a tilt throws light into windows or driver sightlines. In parking lots, the simulation places poles from the aisle layout so that light lands between parked cars instead of on their roofs.
From lux to watts: the energy side
Every lux target on this page becomes an energy number. A 100 W luminaire on a 10-hour night profile draws about 1 kWh per fixture per night. Multiply by fixture count, apply battery depth of discharge and the autonomy days the site needs, and you have the battery; the site's worst-month solar resource then sets the panel. We chain the lighting model into that energy balance before quoting, because the two cannot be specified separately. Our lighting design tool and IES simulation tool run the same arithmetic, and the controller sizing calculator finishes the electrical side.
Weather, dirt, and the derate nobody prices
Does weather belong in the model? Rain barely matters at road level; the scattering effect on ground illuminance is small. Dirt matters a lot. We build a light-loss factor of roughly 0.7–0.8 into every model, covering lens soiling and lumen depreciation over the service interval, because a design that only works on a clean luminaire in week one is not a design. The same discipline applies on the energy side: panel soiling and winter irradiance are derated before the battery is sized, not discovered in year two.
What this page does not cover
Sports lighting, indoor lighting, and grid-tied lighting design follow different standards and different tools. This page covers DC solar street and parking lighting, which is what we build every day. For a specific site, send us the layout and the lighting requirements; or start with the all-in-one solar street light line, where luminaire, panel, and battery are already matched to each other and the mismatch above cannot happen by accident.