Live Demo — Lumens to Foot-Candles Converter
Choose a conversion direction, enter luminaire power and efficiency, and instantly check average illuminance against road lighting standards.
Lumens to Foot-Candles Converter
Free professional photometry converter for solar lighting design. Convert a luminaire's total luminous flux into the average road-surface illuminance in foot-candles and lux, or work backwards from a target illuminance class (branch road ≥1.4 fc, secondary ≥1.9 fc, arterial ≥2.8 fc) to the luminous flux or power your luminaire must deliver.
Key Features
Dual Conversion Mode
Switch between Power → Illuminance and Target Illuminance → Power so you can verify a design or dimension a luminaire.
Luminaire Power & Efficacy
Enter luminaire power and luminous efficacy (Φ = P × η_lm, LED typically 130-180 lm/W) to get total luminous flux.
Lighting Area Geometry
Define the road width and pole spacing so the illuminated area per lamp (A = width × spacing) reflects your layout.
Utilization & Maintenance Factors
Account for the utilization factor CU (0.4-0.7) and maintenance factor MF (0.7-0.8) that connect raw flux to usable illuminance.
Average Illuminance Result
Get the average illuminance in both foot-candles and lux (1 fc = 10.7639 lux) with a clear verdict against the target class.
Standards Compliance Table
Consult the built-in road-lighting reference for average illuminance and uniformity by road class (EN 13201).
Technical Specifications
| Platform | HTML5 Web App | Android (via WebView) |
| Core Calculation | Φ = P × η_lm; E_avg = Φ × CU × MF / A; Φ = E_target × A / (CU × MF); 1 fc = 10.7639 lux |
| Luminaire Power | 1 W and up |
| Luminous Efficacy | 50 - 180+ lm/W (LED typical 130-180 lm/W) |
| Road Width | ft (from 3 ft) |
| Spacing | ft (from 16 ft) |
| Utilization Factor CU | 10% - 90% (typical 0.4 - 0.7) |
| Maintenance Factor MF | 40% - 100% (typical 0.7 - 0.8) |
| Illuminated Area A | Road width × spacing (ft²) |
| Industry Standards | EN 13201, IES RP-8, CIE |
| Output | Average illuminance (fc & lux) or required luminous flux / power for the target road lighting class |
Frequently Asked Questions
What is the difference between lumens and foot-candles?
A lumen (lm) measures total luminous flux — the entire amount of light a source emits — while a foot-candle (fc) measures illuminance, the light arriving on a surface. 1 fc = 1 lm/ft² = 10.7639 lux, so converting between them needs the lit surface area, which is exactly what this calculator does.
How is luminous efficacy used in the conversion?
Luminous efficacy (lm/W) converts electrical power into light output via Φ = P × η_lm. For example, a 100 W LED at 150 lm/W produces 15,000 lm. High-efficacy LEDs (130-180 lm/W) with lens-based photometric control let solar street lights meet illuminance standards with less power.
What do the utilization and maintenance factors represent?
CU is the fraction of emitted light that actually reaches the target road area (typically 0.4-0.7), and MF accounts for dirt accumulation and lumen depreciation over time (typically 0.7-0.8). Both are always below 1, so they reduce the flux available to produce illuminance.
What do the road-class illuminance thresholds mean?
The calculator references typical standards: expressways and arterial roads ≥2.8 fc, secondary roads ≥1.9 fc, branch roads ≥1.4 fc and courtyards/sidewalks ≥0.9 fc, with uniformity ≥0.3-0.4. Comparing your result against these classes tells you whether the design meets, exceeds or falls short of the target for that road type.
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