What Is Luminous Flux?
Luminous flux, or luminous power, is the measure of the perceived power of light. It differs from the measure of the total power of light emitted, termed ‘radiant flux‘ in that the former takes into account the varying sensitivity of the human eye to different wavelengths of light.
In other words, it is photometrically weighted radiant flux (power). The SI unit of luminous flux is the lumen (1m).
One lumen is defined as the luminous flux of light produced by a light source that emits 1(one) cd of luminous intensity over a solid angle of 1 sr.
In other systems of units, luminous flux may have units of power. ‘Lumen‘ is the unit of luminous flux, defined as flux emitted through a unit solid angle (one steradian) from a directional unit point source of 1 cd.
To avoid reference to candela, and to use as a photometric base unit, the lumen may be defined as the luminous flux of monochromatic radiant energy whose radiant flux is 1/683 W and whose frequency is 540 x 1012 Hz (closely equal to a wavelength of 555 nm).
As with luminous intensity, the luminous flux of light with other wavelengths can be calculated using the CIE photometric Curve
What Are Lumens?
Lumens are denoted by lm are a measure of the total amount of visible light to the human eye from a light source or lamp.
The higher the lumen rating the “brighter” the lamp will appear or we can say the more lumens in a light bulb, the light is brighter.
What Do Lumens Mean?
Lumens measure how much light you are getting from a bulb. More lumens means it’s a brighter light; fewer lumens means it’s a dimmer light.
Luminous Energy
Luminous energy is the energy emitted or propagated in the form of light; the product of luminous flux and its duration, measured in lumen-hours or lumen-seconds.
In other words, it is the total radiant energy emitted by a source, evaluated according to its capacity to produce a visual sensation. It is photometrically weighted radiant energy.
How Bright Is 1000 Lumens?
One lumen is approximately equal to the amount of light put out by one birthday candle that’s one foot away from you.
To help you get an idea of the lumen scale, a standard 60-watt bulb puts out around 750-850 lumens of light. If you’re choosing bulbs for task lighting, look for bulbs with 1000 lumens or more.
Luminous Flux Vs. Lumens
| Sr No. | Luminous Flux | Lumens |
| 1 | Luminous flux is the quantity of the energy of the light emitted per second in all directions. | Lumens are denoted by lm are a measure of the total amount of visible light to the human eye from a light source or lamp. |
| 2 | The lumen is the standard unit of luminous flux. | The lumen (symbol: lm) is the SI derived unit of luminous flux |
| 3 | Luminous flux is often used as an objective measure of the useful light emitted by a light source and is typically reported on the packaging for light bulbs, although it is not always prominent. | Lumens used in a house depends on a number of factors including; room size and shape, ceiling height, colour scheme or interior, type of lamps & fitting, task areas and needs of the user. |
| 4 | It is the quantity characteristic of radiant flux which expresses its capacity to produce visual sensation evaluated according to the values of relative luminous efficiency for the light-adapted eye:
a) Effective luminous flux (øn) — Total luminous flux which reaches the working plane. b) Nominal luminous flux (ø0) — Total luminous flux of the light sources in the interior. |
In other words, it is an SI unit of luminous flux. The luminous flux emitted within unit solid angle (one steradian) by a point source having a uniform intensity of one candela.
Lumens used in a house depends on a number of factors including; room size and shape, ceiling height, colour scheme or interior, type of lamps & fitting, task areas and needs of the user. As a general guide; below are the lumens required for different room settings per 10 sq ft. In many cases, a mixture of general and task lighting will be required. |
Frequently Asked Questions about Luminous Flux and Lumens
What is the difference between luminous flux and lumens?
Luminous flux is the total quantity of light energy emitted per second in all directions, while lumens specifically measure the total amount of visible light perceived by the human eye from a light source or lamp.
How are lumens measured?
Lumens are quantified using photometric measurements that take into account the varying sensitivity of the human eye to different wavelengths of light. The unit of measurement for lumens is the lumen (lm).
How does the brightness of a light bulb relate to lumens?
The higher the lumen rating of a light bulb, the brighter the light will appear. Conversely, a lower lumen rating indicates a dimmer light output.
Can you provide a reference point for understanding lumens?
One lumen is approximately equivalent to the amount of light emitted by one birthday candle positioned one foot away. For instance, a standard 60-watt bulb typically produces around 750-850 lumens.
What factors influence the number of lumens needed in a household setting?
Several factors determine the appropriate number of lumens for household lighting, including room size and shape, ceiling height, color scheme, types of lamps and fixtures, specific task areas, and user preferences.
How can I calculate the total luminous energy emitted by a light source?
Luminous energy, which is the product of luminous flux and its duration, can be measured in lumen-hours or lumen-seconds. It represents the total radiant energy emitted by a source, weighted according to its capacity to produce a visual sensation.
Are there specific guidelines for selecting the right level of illumination for different room settings?
Yes, while the ideal number of lumens varies based on individual preferences and room characteristics, there are general recommendations for different room settings per 10 square feet. However, a combination of general and task lighting is often necessary for optimal illumination.
