How to Size Solar Street Lights: LED Power, Battery, Panel, and Spacing Guide
Correctly sizing solar street lights ensures adequate illumination, reliable overnight operation, and years of maintenance-free service. Undersized lights leave dark spots; oversized lights waste money. This guide covers every sizing parameter.
Step 1: Determine Required Illumination
| Road Type | Required Lux | LED Power | Pole Height | Spacing |
|---|---|---|---|---|
| Pathway / garden | 5-10 lux | 20-40W | 3-4m | 10-15m |
| Residential street | 10-15 lux | 40-80W | 5-7m | 25-35m |
| Collector road | 15-20 lux | 80-120W | 8-10m | 30-40m |
| Main road / highway | 20-30 lux | 120-200W | 10-12m | 35-50m |
| Parking lot | 10-20 lux | 80-150W | 8-10m | 20-30m |
Step 2: Size the Battery
Battery capacity = LED watts x operating hours x autonomy nights / DoD / efficiency
Example: 60W LED, 10 hours/night, 3 nights autonomy, 80% DoD (LiFePO4), 90% efficiency:
60 x 10 x 3 / 0.80 / 0.90 = 2,500 Wh = 2.5 kWh battery
At 12.8V LiFePO4: 2,500 / 12.8 = 195 Ah
Step 3: Size the Solar Panel
Panel watts = Daily LED consumption / Peak sun hours / charge efficiency x safety margin
Example: 600 Wh/night, 6 PSH (UAE), 90% efficiency, 1.3 safety margin:
600 / 6 / 0.90 x 1.3 = 144W solar panel
Step 4: Choose the Right Light Type
All-in-One
Panel, battery, LED, and controller in a single unit. Best for residential streets and pathways. Felicity Solar all-in-one range: 30W to 200W.
Split Type
Panel mounted separately from the LED head. Best for high-power applications (100W+) that need larger panels than can fit on top of the light head.
Step 5: Configure Dimming Schedule
Intelligent dimming extends battery life and reduces costs:
| Time Period | Brightness | Power Draw (60W) |
|---|---|---|
| Sunset - 10 PM | 100% | 60W |
| 10 PM - 5 AM | 50% | 30W |
| 5 AM - Sunrise | 100% | 60W |
With this schedule, the 60W light uses only 420 Wh per night instead of 600 Wh — a 30% reduction that allows a smaller battery and panel.
Pole Spacing Formula
For uniform illumination: Spacing = Pole height x 3 to 4
A 7m pole: spacing = 7 x 3.5 = approximately 25m. Adjust for road width — wider roads need closer spacing or lights on both sides.
Frequently Asked Questions
What LED power do I need for a residential street?
A residential street typically needs 40-80W LED at 5-7m pole height with 25-35m spacing. A 60W Felicity Solar all-in-one street light provides 6,000-7,000 lumens, adequate for most residential applications.
How many nights of autonomy should a solar street light have?
3 nights minimum for the Middle East, 5 nights for tropical Africa during rainy season. This ensures the light operates at full brightness even after several consecutive cloudy days. Intelligent dimming can extend this further.
Should I use all-in-one or split-type solar street lights?
All-in-one is simpler and cheaper for residential streets (up to 80W LED). Split-type is better for main roads and highways (100W+ LED) that need larger solar panels than can be integrated on top of the light head.
