Convert lumens to lux, lux to lumens, lumens to candela, candela to lux, watts to lumens, lux to foot-candles, and calculate complete room lighting requirements — all 5 modes using CIE and IES verified photometric formulas.
Total light output of the sourceEnter a valid value.
Surface area receiving the lightEnter a valid area.
Select conversionSelect direction.
Total light outputEnter a valid value.
Full beam angle (omnidirectional = 360)Enter angle 1–360.
Select conversion directionSelect direction.
Lamp wattageEnter a valid value.
Luminous efficacy of sourceSelect lamp type.
Enter your lamp's lm/W ratingEnter valid efficacy.
Select conversion directionSelect direction.
Illuminance value to convertEnter a valid value.
Calculate total lumens and number of fixtures required for any room using the Lumen Method (IES).
Room length in metersEnter valid length.
Room width in metersEnter valid width.
Target lux for the spaceSelect target lux.
Enter your required lux levelEnter valid lux.
Room surface reflectance factorSelect CU.
Accounts for dirt and lamp agingSelect LLF.
Rated lumens of each lamp/fixtureEnter fixture lumens.
Result
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⚠️ Disclaimer: Results use CIE and IES standard photometric formulas. Actual lighting performance depends on fixture distribution, mounting height, room geometry, and surface reflectance. Consult a certified lighting designer (LC) for critical applications.
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📚 Sources & Methodology
All photometric formulas are verified against:
CIE 15:2004 — International Commission on Illumination: Colorimetry, photometric units (lumen, lux, candela) cie.co.at
IES RP-1-20 — Illuminating Engineering Society: Recommended Practice for Office Lighting, lux targets and lumen method ies.org
IES RP-8-14 — Roadway and Area Lighting, outdoor lux standards ies.org
NIST SP 250-37 — Photometric characterization of lamps and luminaires nist.gov
Lumens vs Lux vs Candela: The Three Light Measures
Lumens (lm) measure total light output — the total visible light emitted by a source in all directions. A light bulb package shows lumens so you can compare brightness regardless of direction. Lux (lx) measures illuminance — how much light falls on a surface per square meter. Lux = Lumens / Area. A 1000-lumen lamp lighting 10 m² gives 100 lux. Candela (cd) measures luminous intensity — light emitted per steradian in a specific direction. Spotlights and LEDs are often rated in candela for their beam direction.
Core Photometric Formulas (CIE)
Lux = Lumens / Area (m2) [illuminance]Lumens = Lux x Area (m2) [flux from illuminance]Candela = Lumens / (2pi x (1-cos(theta/2))) [directional intensity]Lux = Candela / Distance^2 [inverse square law]Foot-candles = Lux / 10.764 [US unit conversion]Lumens = Watts x Efficacy (lm/W) [power to light]Total lumens = Lux x Area / (CU x LLF) [lumen method, IES]
Lighting Level Standards by Application (IES)
Application
Recommended Lux
Foot-candles
Typical Fixture
Moonlit night
0.001 lux
0.0001 fc
Natural
Hallway / corridor
50–100 lux
4.7–9.3 fc
LED downlight
Living room
150–300 lux
14–28 fc
Ceiling fixture
Bedroom
100–300 lux
9.3–28 fc
Ceiling/lamps
Office (IES RP-1)
300–500 lux
28–46 fc
T8/LED troffer
Kitchen work surface
500–750 lux
46–70 fc
Under-cabinet LED
Retail / showroom
750–1500 lux
70–139 fc
Track/accent
Workshop / precision
1000–2000 lux
93–186 fc
High-bay LED
Surgery / dental
5000–10000 lux
465–929 fc
Surgical luminaire
Overcast daylight
1000 lux
93 fc
Natural
Full daylight
10,000–25,000 lux
929–2322 fc
Natural
Direct sunlight
~100,000 lux
~9290 fc
Natural
LED vs Incandescent Lumen Equivalents
Old Incandescent
LED Equivalent
Lumens
Energy Saved
25W incandescent
3–4W LED
~250 lm
84%
40W incandescent
5–6W LED
~450 lm
85%
60W incandescent
8–9W LED
~800 lm
86%
75W incandescent
10–11W LED
~1100 lm
86%
100W incandescent
13–15W LED
~1600 lm
86%
150W incandescent
20–22W LED
~2600 lm
86%
200W incandescent
25–28W LED
~3400 lm
87%
The Lumen Method for Room Lighting Design
The IES Lumen Method calculates required total lumens: Total Lumens = Target Lux × Area / (CU × LLF). The Coefficient of Utilization (CU) accounts for how much light actually reaches the work plane based on room shape and surface reflectance — typically 0.45 to 0.75. The Light Loss Factor (LLF) accounts for lamp lumen depreciation and dirt accumulation over time — typically 0.7 to 0.85. Dividing total lumens by fixture lumens gives the number of fixtures.
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Practical tip: For general residential lighting, a quick rule of thumb is 20–30 lumens per square foot (215–320 lm/m²) for ambient light in living areas, and 50–75 lm/ft² (538–807 lm/m²) for kitchens and offices. These estimates assume standard 8-foot ceilings and light-colored walls. Use the Room Lighting Design mode above for precise calculations.
❓ Frequently Asked Questions
Lux = Lumens / Area (m2). A 1000 lumen lamp illuminating 5 m2 evenly = 200 lux. Lumens measure total light output; lux measures light density on a surface. As you increase the illuminated area, the lux decreases even though the lumens stay the same. Use the Lumens to Lux tab above for any combination.
Lumens = Lux x Area (m2). To achieve 300 lux in a 15 m2 room: ideal lumens = 300 x 15 = 4,500 lm. In practice, account for CU (0.65) and LLF (0.75): actual lumens needed = 4500 / (0.65 x 0.75) = 9,231 lm. Use the Room Lighting Design tab for full calculations including CU and LLF.
Lumens (lm) = total light output. Lux (lx) = lumens per square meter on a surface (illuminance). Candela (cd) = lumens per steradian in one direction (luminous intensity). All related: Lux = Lumens/Area. Lux = Candela/Distance^2. A lamp's lumens are fixed; lux varies with how spread out the light is; candela varies with direction.
Lumens = Watts x Efficacy (lm/W). LED: 80-130 lm/W. CFL: 50-70 lm/W. Halogen: 15-25 lm/W. Incandescent: 10-15 lm/W. A 10W LED at 100 lm/W = 1000 lm. Same lumen output as a 70W incandescent at 14 lm/W = 980 lm. Use the Watts to Lumens tab and select your lamp type for instant results.
Foot-candles = Lux / 10.764. Lux = Foot-candles x 10.764. One foot-candle = illuminance from one candela at one foot = 10.764 lux. Office standard 500 lux = 46.5 fc. Retail 1000 lux = 92.9 fc. US codes often specify foot-candles; international codes use lux. Use the Lux/Foot-candles tab above for any value.
Required lumens/m2 equals required lux (they are the same unit for ideal uniform illumination). Hallways: 50-100 lm/m2. Living rooms: 150-300. Offices/kitchens: 300-500. Retail: 500-1000. Workshops: 500-2000. These are bare minimum; actual fixture lumens must be higher to account for CU (0.5-0.75) and LLF (0.7-0.85) factors.
Lux = Candela / Distance^2 (inverse square law for point sources at perpendicular incidence). A 500 cd spotlight at 2 meters: 500/4 = 125 lux. At 5 meters: 500/25 = 20 lux. Doubling distance = quarter the lux. For angled incidence: Lux = Cd x cos(theta) / D^2. Use the Lumens/Candela tab above with the cd to lux direction.
A 60W incandescent produces approximately 800 lumens (14 lm/W efficacy). An LED replacement producing 800 lm uses only 8-9W (100 lm/W). Always compare bulbs by lumens, not watts. 40W incandescent = 450 lm. 75W = 1100 lm. 100W = 1600 lm. LED equivalents use 86% less energy for the same lumen output.
Luminous efficacy (lm/W) measures lighting efficiency - visible light produced per watt. Higher is better. LED high-efficiency: 100-130+ lm/W. LED standard: 80-100 lm/W. CFL: 50-70 lm/W. T8 fluorescent: 80-100 lm/W. Halogen: 15-25 lm/W. Incandescent: 10-15 lm/W. Maximum theoretical limit for white light: ~250-350 lm/W. Most daylight-balanced LEDs are 90-130 lm/W.
IES Lumen Method: Total Lumens = Target Lux x Area / (CU x LLF). Example: 4m x 5m office (20 m2), 500 lux target, CU=0.65, LLF=0.75: Total = 500 x 20 / (0.65 x 0.75) = 10,000/0.4875 = 20,513 lm. With 800 lm per LED troffer: 20,513/800 = 26 fixtures. Use the Room Lighting Design tab for automatic calculation.
For a point source with full beam angle theta: Lumens = (mcd/1000) x 2 x pi x (1 - cos(theta/2)). A 3000 mcd LED with 30-degree beam: Lumens = 3 x 2 x 3.14159 x (1 - cos(15deg)) = 3 x 6.283 x 0.0341 = 0.643 lm. LEDs are rated in mcd for directional intensity; the beam angle is needed to convert to total lumen output.
Per IES RP-8: building entrance/exit areas 50-100 lux. Parking lots and driveways 10-50 lux. Walkways 5-20 lux. Security-critical areas 50-200 lux. Perimeter fence lighting 20-50 lux. In foot-candles: 1-5 fc for parking, 4.6-9.3 fc for entrances, 4.6-18.6 fc for security areas. Modern LED fixtures make these levels energy-efficient.