Definition of lumens:

Lumens – the unit of luminous flux. A point light source having a luminous intensity of 1 candela (cd) emits a luminous flux of “1 lumen” in a unit solid angle (1 steradian). English abbreviation (lm).

How bright is 100 lumens?
The so-called lumens are simply the brightness of a candle that is outside a meter of a meter. 100 lumens also means the light that 100 candles emit in a square meter! An ordinary 40-watt incandescent bulb with a luminous efficiency of about 10 lumens per watt can emit 400 lumens of light. At 40 volts for a 40-watt incandescent bulb, the luminous flux is 340 lumens. Luminous flux is the ability to describe the intensity of visual response from source radiation in a unit of time. The unit is lumens, also known as brightness.

How Bright is a Lumen?

While you may be used to comparing light bulbs and products by wattage, a new unit of measurement has taken the spotlight: the lumen. So, what is a lumen? Although it’s difficult to compare watts and lumens directly, we want to share some guidelines on understanding the relationship between them.

What is a Lumen?
Lumens have become the most prominent unit of measurement for brightness, but what exactly are they? A lumen is a unit that describes the amount of light provided over a given area. Each lumen is about equal to the light output of a single candle. Essentially, a lumen is a measurement of brightness itself.

The brightness, or lumen levels, of the lights in your home may vary widely, so here’s a rule of thumb:

  • To replace a 100 watt (W) incandescent bulb, look for a bulb that gives you about 1600 lumens. If you want something dimmer, go for less lumens; if you prefer brighter light, look for more lumens.
  • Replace a 75W bulb with an energy-saving bulb that gives you about 1100 lumens
  • Replace a 60W bulb with an energy-saving bulb that gives you about 800 lumens
  • Replace a 40W bulb with an energy-saving bulb that gives you about 450 lumens.

Lumens vs. Watts
The fundamental difference between these two units is what exactly each of them measure. We just learned that lumens measure the output or “brightness” of a given light source. On the contrary, watts measure the amount of energy required to produce a particular level of brightness.

While a comparison between watts and lumens isn’t apples to apples, some correlations can be made to help you choose the lighting solution best for you (see chart below). For instance, if a standard 40-watt bulb delivers about 450 lumens of light (actual light output varies by product and manufacturer), we can assume that 1-watt of consumption is necessary for an output of about 11.25 lumens.

Lumen Brightness Scale

So how many lumens do you really need? This is my subjective opinion:

  • 1 lumen. About 10 times brighter than moonlight (depending on how wide the beam is – a wide beam spreads out the light and looks dimmer). Only useful in pitch black darkness – it’s barely enough to light up a trail but is enough for stumbling to the toilet in the middle of the night without dazzling your dark-adjusted eyes. It is however, more than enough for reading a book (the book is less than 1 foot away, so the spot is smaller and brighter). An average 2x AA battery flashlight will give you a few days of runtime on 1 lumen.
    This is too low for the maximum brightness of a useful flashlight, but is good as a low setting on a brighter flashlight.
  • 3 lumens. While still low, this is significantly more useful than 1 lumen.
    Minimum useful brightness for a keychain (coin/button cell) light.
  • 10 lumens. As bright as a candle, though it is hard to compare because a candle’s light is not focused into a tight beam. Enough for most camping, backpacking, hiking activities. Also bright enough for emergency preparedness – eating a meal during a blackout, fixing a car engine. An average 2x AA flashlight will give you over 24 hours of runtime.
    This is a good brightness for a keychain (coin/button cell or 1x AAA) light.
  • 30 lumens.
    Minimum brightness for a general purpose flashlight. Unfortunately, many cheap supermarket flashlights are dimmer than this.
  • 100 lumens. Bright enough for most urban and suburban use – shining a spot on the road so that car drivers can see you, temporarily blinding attackers, scanning a small backyard for intruders. An average 2x AA flashlight will give you 5 to 10 hours of runtime.
    This is a good brightness for a pocket (1x AAA, 1x AA) flashlight or headlamp.
  • 300 lumens. Bright enough for most uses, including searching for people and animals over 50 meters away (depends on how wide the beam is), comfortably lighting up a small room by bouncing the light off the ceiling, bicycle lamp. An average 2x AA flashlight will give you 1 to 2 hours of runtime.
    This is a good brightness for a medium-sized (2x AA, 1x CR123A) flashlight.
  • 1000 lumens. Nice to have, but you won’t need it unless you are in law enforcement, the military or emergency services. Today’s 1x 18650 and 4x AA flashlights routinely reach 1000 lumens anyway, so all other features being equal, why not choose the 1000 lumen flashlight? You never know when you might need 1000 lumens, and it’s a lot of fun.
    This is a good brightness for a medium-sized (4xAA, 1×18650) flashlight.
  • 3000 lumens. Useful for lighting up a large area, such as a factory workspace, construction site or ship yard. Bounce the beam off a ceiling or wall for non-glaring light.
    These are 2x to 4×18650 flashlights, which are significantly bulkier than other flashlights. 

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