Lumens are the unit for measure used to demonstrate the total quantity of visible light emitted by a light source. It comes from the Latin word for light and this metric is used worldwide to denote how bright a light is.

When most household lighting mainly relied on incandescent bulbs, consumers would refer to the amount of wattage the bulb had to determine the brightness. A 60-watt bulb would be brighter than a 40-watt bulb for example. However, as technology developed in the lighting industry bringing us fluorescent and LED technology, the relationship between energy usage (watts) and light output (brightness) changed dramatically. A 9-watt LED bulb for example can produce the same light output as an older 60-watt incandescent bulb.

The lumen measurement for brightness has now been adapted by the lighting industry to provide a more accurate and consistent means of measuring brightness which can be applied to all types of bulbs and light fittings, regardless of the technology they are made from. When purchasing any modern light source, you should always look for the lumen rating rather than the wattage in order to understand how much light it will produce.

The Technical Definition

The lumen (symbol: lm) is known as an SI (International System of Units) which is a derived unit of luminous flux. Luminous flux measures the perceived power of light, or the amount of light energy that is useful for illumination. 

One lumen can be defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian. This in layman's terms translates to: The higher the amount of lumens, the brighter the light.

Does A Higher Amount Of Lumens Mean A Brighter Light?

Yes it does.  A higher lumen rating always means a brighter source of light.  Lumens measure the total amount of light that is emitted in all directions from a light source. A 800 lumen bulb for example will produce twice as much light as one that is 400 lumens.

However, the perceived brightness from the light can be influenced by how the lumens have been focused and distributed:

• Directional vs. Non-Directional Light: A spotlight that focuses 1,000 lumens into a narrow beam will appear to be much brighter than a non-directional bulb that distributes the same 1,000 lumens evenly across a wide area. 
• Color Temperature: Light that has a cooler (bluer) color temperature (such as 4000K-6000K cool white or daylight light) will feel brighter and more intense than light that has a 2700K-3000K colour temperature (very warm white to warm white), even if both lights have exactly the same number of lumens.

How bright would 1000 lumens be?

1,000 lumens is considered to be very bright for the majority of indoor and personal use.  In terms of an incandescent bulb a 75-100 watt bulb would have around 1000 lumens.  A wide majority of powerful high end torches or flashlights would start at 1000 lumens and these are powerful enough to see objects hundred of feet away.  Whilst 1000 lumens will often be too bright for a small indoor room industrial or outdoor stadium lighting can sometimes reach in the thousands for the lumens measurement.

How Many Lumens is a Phone Flashlight/Torch?

The flashlight (or torch) in a smartphone is designed for close-range use and will typically measure between 40-100 lumens.  The perceived brightness from a smartphone flashlight appears to be high for the lumen count as it is a small focused light narrowed by the camera lens.

How Many Lumens is needed to Make a Room Bright?

The number of lumens required to illuminate a room will depend on the room's size, what it is being used for, the ceiling height, and the color of the walls.

Below is a table with some recommendations for common room types.  This is based on the assumption that they will have the average ceiling heights and colored walls found in each of these rooms: