What Is a Lumen? A Plain Definition with Real Lighting Examples
Lumens in plain words: what a lumen measures, how it differs from watts, lux and candela, typical lumen values for bulbs, street lights and floodlights, and how to use them.
Key points
- A lumen (lm) measures the total amount of visible light a source gives out in all directions.
- Watts measure power used; lumens measure light produced. Lumens per watt (lm/W) is efficiency.
- Lux is lumens landing on one square metre; candela is intensity in one direction.
- A household LED bulb gives about 800 lm, a residential street light 4,000–8,000 lm and a stadium floodlight over 100,000 lm.
The lumen is the most useful number on any lighting product, and the one most often confused with watts. This guide explains what it means, how it relates to other lighting units, and how to use it when choosing lights.
The definition
A lumen (symbol lm) is the unit of luminous flux: the total amount of visible light a source emits in all directions, weighted for how sensitive the human eye is to each colour. A lamp that gives 1,000 lm puts out twice as much visible light as one that gives 500 lm.
Formally, one lumen is the light from a source of one candela spread through one steradian of solid angle. In practice, you can think of it as “how much light comes out”.
Lumens vs watts
For a hundred years people chose bulbs by watts, because with incandescent lamps more watts meant more light. With LEDs this no longer works. Watts measure the electrical power used; lumens measure the light produced. The ratio between them is efficacy, in lumens per watt:
| Light source | Typical efficacy |
|---|---|
| Incandescent bulb | 10–17 lm/W |
| Halogen | 15–25 lm/W |
| Compact fluorescent | 50–70 lm/W |
| Fluorescent tube (T8) | 70–100 lm/W |
| Metal halide | 60–100 lm/W |
| High pressure sodium | 80–140 lm/W (lamp only) |
| Modern LED fixture | 120–180 lm/W |
So a 10 W LED can give as much light as a 60 W incandescent bulb. To convert between them, see lumens to watts.
Lumens vs lux vs candela
These three are often mixed up:
- Lumen (lm): total light out of the source
- Lux (lx): light landing on a surface, in lumens per square metre
- Candela (cd): intensity of light in one particular direction
A useful picture: lumens are the water coming out of a hose, lux is how wet the ground gets per square metre, and candela is how strong the jet is in one direction. A spotlight and a floodlight with the same lumens give the same total light, but the spotlight concentrates it into high candela in a narrow beam and high lux on a small area.
In the US, illuminance is often given in foot-candles: lumens per square foot. One foot-candle is about 10.76 lux. See foot-candles to lux.
Typical lumen values
| Light | Typical lumens |
|---|---|
| Candle | about 12 lm |
| Solar garden stake light | 5–50 lm |
| Household LED bulb (60 W equivalent) | about 800 lm |
| 2×2 LED panel | 3,000–4,500 lm |
| LED tube, 4 ft | 1,800–2,400 lm |
| Residential LED street light (30–60 W) | 4,000–9,000 lm |
| Main-road LED street light (120 W) | 15,000–19,000 lm |
| 150 W LED high bay | 20,000–25,000 lm |
| 1000 W LED stadium floodlight | 130,000–160,000 lm |
Lamp lumens vs fixture lumens
A bulb’s lumen rating is the light from the bare lamp. When a lamp is put in a fixture, some light is lost in the reflector, lens and housing. LED fixtures are rated in fixture (system) lumens, which is what reaches the outside. When comparing an LED fixture with an old lamp, compare fixture lumens with the old fixture’s output, not the bare lamp rating. This is one reason LED fixtures can replace older lamps with fewer lumens on paper.
Lumens over time
All light sources lose output as they age. LEDs fade slowly; their life is often stated as L70, the hours until output falls to 70% of the initial lumens. LED makers test this under the LM-80 method and project it with TM-21, which is why good suppliers can state L70 hours with some confidence.
How to use lumens when buying lights
For a room or building: decide the lux level needed, multiply by the area, and allow for losses. For example, an office of 50 m² at 500 lux needs about 25,000 lm on the work plane, which, after losses, means roughly 35,000–40,000 fixture lumens. The high bay lighting calculator does this for warehouses and factories.
For roads and car parks: the light distribution matters as much as lumens. A well-designed optic puts the lumens on the road rather than into the sky or onto houses.
For floodlights: compare lumens and beam angle together. Narrow beams reach further; wide beams cover close areas.
For solar lights: be wary of very high lumen claims on small solar lights. The panel and battery limit how many lumens can be produced for how many hours.
Lumens and colour temperature
Two lights with the same lumens can look different in brightness. Cooler white light of 5000 K often looks brighter to the eye than warm white of 2700 K at the same lumens, although lumen ratings already allow for the eye’s sensitivity. See the colour temperature chart for how CCT affects appearance.
Lumens and energy savings
Because LED fixtures give far more lumens per watt, replacing older lighting with LED of the same useful light output saves a large share of the energy. A 400 W metal halide high bay can typically be replaced by a 150–200 W LED. The LED retrofit savings calculator estimates the savings for your hours and tariff.
Our products
When you compare our lights with others, ask for system lumens measured from the complete fixture, so you compare like with like. Our LED panel lights, high bays, floodlights and street lights all come with photometric data on request.
Sources
Frequently asked questions
What is a lumen in simple terms?
A lumen is the unit for the total amount of visible light a lamp or fixture gives out. More lumens means more light, whatever the wattage.
How many lumens is bright?
For a room, a single bulb of about 800 lumens is typical. For outdoor areas, a wall light might give 1,000–3,000 lumens, a street light 4,000–20,000 and a large floodlight tens of thousands. Whether it looks bright also depends on the area and distance.
Is a lumen the same as a watt?
No. Watts measure the power a light uses. Lumens measure the light it gives. An LED might give 130–160 lumens per watt, an old incandescent bulb only about 15.