Lumen to Lumen Converter
Quickly convert from Lumen to Lumen.
How to convert
Formula:
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Luminous flux measures the total amount of visible light emitted by a source in all directions, weighted by the human eye's sensitivity.
Where is it used?
• Consumer Lighting — LED bulb packaging specifies lumens to indicate brightness, replacing the old watt-based system. A '60W equivalent' LED produces ~800 lm while consuming only 8–10 W.
Examples:
• 1 lumen (lm) = 1 cd·sr
• 1 lux (lx) = 1 lm/m²
Luminous flux measures the total amount of visible light emitted by a source in all directions, weighted by the human eye's sensitivity. It is the key metric on light bulb packaging and the starting point for lighting design calculations — connecting the power of a light source to its useful light output.
Luminous flux is the photometric measure of the power of visible light emitted by a source, integrated over all directions and weighted by the luminosity function (human eye spectral response). The SI unit is the lumen (lm). Related to it are: the candela·steradian (cd·sr), which is mathematically equivalent to the lumen (1 lm = 1 cd·sr); and lumens per watt (lm/W), the luminous efficacy that describes how efficiently a source converts electrical power into visible light.
Where is it used?
- Consumer Lighting — LED bulb packaging specifies lumens to indicate brightness, replacing the old watt-based system. A '60W equivalent' LED produces ~800 lm while consuming only 8–10 W.
- Architectural Lighting Design — Lighting designers calculate required luminous flux to achieve target illuminance levels (lux) in rooms, using the lumen method or point-by-point analysis.
- Projectors & Cinema — Projector brightness is specified in ANSI lumens or ISO lumens; a typical classroom projector delivers 3,000–5,000 lm, while cinema projectors produce 20,000–60,000 lm.
- Automotive Lighting — Headlamp luminous flux requirements are specified in regulations (ECE R112, SAE standards); modern LED headlamps produce 1,500–3,500 lm per lamp.
- Horticulture & Plant Lighting — While specialist plant growth lighting uses PPFD (photosynthetic photon flux density in μmol/m²/s), lumen output is still used to compare general-purpose grow lights.
Common Conversion Mistakes
Equating watts with lumens
Watts measure electrical power consumption, not light output. Luminous efficacy varies widely: an incandescent bulb yields ~15 lm/W; a compact fluorescent ~60 lm/W; a modern white LED up to ~200 lm/W. A 10 W LED can produce more lumens than a 60 W incandescent. Always compare lumens, not watts, when evaluating light output.
Confusing luminous flux (lm) with luminous intensity (cd)
Luminous flux (lm) is the total light emitted in all directions. Luminous intensity (cd) is the flux per unit solid angle in a specific direction. A floodlight with high total flux may have lower intensity in any given direction than a spotlight with the same total flux focused into a narrow beam. These are different quantities suited to different applications.
Forgetting light loss factors in real installations
The initial lumen output of a lamp decreases over time (lumen maintenance / L70 rating) and is reduced by luminaire efficiency, dirt accumulation, and temperature. Lighting design standards require applying maintenance factors (typically 0.67–0.80) to initial lumens when calculating maintained illuminance.
Using lux and lumens interchangeably
Lumens measure total flux from a source; lux measures flux per unit area at a surface. 1 lux = 1 lm/m². The same 800 lm bulb produces 800 lux on a 1 m² surface directly below it, but only 80 lux spread over 10 m². The relationship depends entirely on distance, direction, and geometry.
Quick Reference Table
| From | To |
|---|---|
| 1 lumen (lm) | 1 cd·sr |
| 1 lux (lx) | 1 lm/m² |
| 1 footcandle (fc) | 10.764 lm/m² (lux) |
| 40 W incandescent | ~450 lm |
| 60 W incandescent equivalent | ~800 lm |
| 100 W incandescent equivalent | ~1,600 lm |
| Efficient LED bulb | 80–150 lm/W |
| Full sphere (4π sr) | 4π cd for isotropic 1 cd source = 12.566 lm |
Frequently Asked Questions
How many lumens do I need for a room?
A common rule of thumb for general residential lighting is 20–50 lm per square foot (215–540 lm/m²). For a 20 m² living room at 300 lux target: required flux = 300 lux × 20 m² = 6,000 lm total (before applying maintenance and luminaire efficiency factors). Task lighting (desks, kitchen counters) typically requires 500–750 lux; corridors and stairways 100–150 lux.
What replaced the watt as the measure of bulb brightness?
The lumen replaced the watt after regulations phased out inefficient incandescent bulbs in the EU (2009–2012) and US. Because LED efficacy varies widely (60–200+ lm/W), wattage no longer reliably indicates brightness. The EU and US now require lumen output on packaging. 'Equivalent' wattage labels are informal marketing references, not technical specifications.
What is luminous efficacy and what values are typical?
Luminous efficacy is lumens per watt (lm/W) — how much visible light a source produces per watt of input power. Theoretical maximum for monochromatic 555 nm light: 683 lm/W. Practical values: incandescent 10–17 lm/W; halogen 15–25 lm/W; CFL 45–75 lm/W; standard LED 80–130 lm/W; best laboratory LEDs >200 lm/W; high-pressure sodium street lights ~130 lm/W.
What is the relationship between lumen and candela?
The candela (cd) is the SI base unit for luminous intensity — flux per solid angle: 1 cd = 1 lm/sr. For a point source emitting uniformly in all directions into the full sphere (4π steradians), total flux = 4π × (intensity in cd) ≈ 12.566 × cd. An isotropic source of 1 cd emits 4π ≈ 12.566 lm total. Directional sources emit the same flux into a smaller solid angle, giving higher cd for the same lm.
Sources & Standards
- CIE 015:2018 — Colorimetry, 4th edition (luminosity function)
- IES TM-30 — Method for Evaluating Light Source Color Rendition
- EU Regulation 874/2012 — Energy labelling of electrical lamps
- NIST Special Publication 250-37 — Photometric calibration
Reviewed by The Unit Hub Editorial Team · March 2026