Since the classic incandescent lamp was taken off the market, consumers lack a clear parameter with which they can assess the brightness of a light source at first glance. In the past, lamps with the same wattage could be relied upon to shine with roughly the same brightness. But these times are over due to the LED. The wattage of an LED retrofit or LED luminaire does not provide any information about its light quantity. This is why luminous flux has now become established as a comparative parameter for determining the amount of light emitted by a light source. But what is behind this physical measured value?? The luminous flux alone can be used to determine whether a lamp provides the desired brightness? Or in other words: How bright are 1000 lumens??
Luminous flux in lumens – The brightness of luminaires and lamps
How much light does a conventional incandescent lamp emit??
To answer these questions, we must first understand what is behind the term lumen: lumen is the unit in which the luminous flux is specified. This describes the amount of radiation in the range of visible light that a light source emits. In simple terms, the lumen value indicates how much light an illuminant emits. At first it seems to be a reliable reference value for the comparison of different illuminants. Especially since the wattage no longer provides a reliable guide to the brightness of a lamp due to the so-called incandescent lamp ban. But how can we compare different light sources with each other?? In other words, how bright does a light source have to be to replace a 75 W incandescent lamp, for example??
Luminous flux in comparison
In the days of the incandescent lamp, it was easy to compare the brightness of different lamps on the basis of their wattage. For LED luminaires, LED retrofits or even energy-saving lamps, the wattage does not provide a clear indication of the brightness of the light source. Here only the unit of the luminous flux in lumens helps further. A 75-watt incandescent lamp – one of the most widely used light sources before the ban on incandescent lamps began – produces a quantity of light approaching 1000 lumens. So, to replace a corresponding light source, an LED or energy-saving lamp with approx. 1000 lumens needed. But is the calculation as simple as that, or do other factors have to be taken into account when comparing lamps??
In fact, it’s not quite that simple. Incandescent lamps emit their light evenly in all directions and have a beam angle of more than 270°. These essential factors for light perception are not taken into account when the luminous flux is specified. This is especially tricky because most LED fixtures and retrofits focus the light more due to their design. Therefore, many LED luminaires and lamps illuminate a smaller solid angle than the classic incandescent lamp. In the field of LED retrofits there are now products that come very close to the incandescent lamp. LED filament lamps in particular are similar to classic incandescent lamps in terms of beam characteristics.
This is how bright 1000 lumens is compared to…
… 700 lumens ..
… and 400 lumens
Let’s take an example to illustrate this: The Euclid PD S dim2warm from the German luminaire manufacturer Bruck emits a total luminous flux of 1000 lumen. This means that the LED pendant luminaire qualifies in principle as a replacement for our example with the 75-watt incandescent lamp. However, it directs its light downwards in a focused manner. As a result, the area below the pendant is brightly illuminated, while the surrounding area and the rest of the room remain relatively dark. Euclid thus provides accentuating zone lighting that is ideal for illuminating a table surface. However, it is not suitable as a room light for basic and general illumination.
1000 lumens are therefore not equal to 1000 lumens. In order to compare the brightness of light sources, the spatial aspect must also be taken into account: How far away is the light source from the illuminated object, at what angle is the light emitted, and how much light hits the illuminated surface? However, this already brings us to the topics of illumination and luminous intensity, which are expressed in lux and luminous intensity, respectively. Candela can be specified. These sizes relate the luminous flux to the illuminated solid angle and the illuminated area. In contrast to luminous flux, however, illuminance cannot be specified as a binding value for every light source, as it depends on the specific room and application situation. The luminous intensity in candela is problematic and is only given for lamps that emit directional light. Only if the room situation, the beam angle of the light sources, etc., are suitable. are known, light sources based on illumination or. Compare luminous intensity.
Luminous flux and the subjective perception of light
The same amount of light has a completely different effect on us against light or dark backgrounds.
The brightness of light sources can generally be compared well using physical measurements such as luminous flux in lumens, although other factors such as z.B. the beam angle, to be considered are. However, the actual perception of brightness is influenced by several other factors. This is illustrated by the example in the picture above. It can be seen very clearly that two scenes with the same equipment – luminaires with the same luminous flux and beam angle – have a different effect simply because of the color and texture of the background. Applied to our home lighting, this means that a luminaire or lamp with 1000 lumens is perceived as more powerful in a bright environment than in an environment with muted and dark colors. Bright surfaces simply reflect light better than dark and especially black surfaces. The latter virtually swallow the light and thus reduce our impression of the brightness of a room.
How well a light source can represent colors influences our subjective perception of light.
In addition, the light spectrum and the color rendering index (CRI) of a light source play a decisive role in our perception of brightness. The light spectrum refers to the color range covered by a light source. A complete light spectrum serves all three primary colors red, blue and yellow and thus contributes significantly to the color rendering of a lamp or luminaire. The latter provides information about how true to life a light source displays colors and contours. A low color rendering value and an uneven light spectrum therefore cause us to perceive colors as pale, which makes us assess the brightness of a light source as darker. This also applies when two lamps objectively emit the same amount of light. A 75 watt lamp with very good color rendering and full light spectrum is always perceived as brighter than a typical fluorescent lamp with comparable light output. The reason is that the latter emits light with a high blue content, which also negatively affects the color rendering value.
So 1000 lumens with a color rendering of Ra=97 work.
So let’s keep in mind: The specification of the luminous flux in lumens is a suitable orientation value to counteract the omission of the wattage as a guideline. Using the lumen values, we can easily determine which light source is suitable as a replacement for our example with the 75-watt incandescent lamp. However, the supposedly exact measured values cannot be easily converted into a brightness perception, since both the beam angle and the design of the luminaire or lamp influence the impression of light. Finally, the color rendering as well as the colorfulness and texture of the background also shape our subjective perception of light.
You have questions about your specific room situation? You are unsure which light source to replace your 75 W incandescent lamp with to achieve a similar impression of brightness? Write to us, we will be glad to help you. Our colleagues from the lighting design department will be happy to support you in finding the best light for your object.
11 thoughts on" Luminous flux explained – How bright are 1000 lumens?? “
I make in my bath-im-mer 2 mirror doors. In each of the doors, a strip is satin-finished on the side in the mirror (Ca. 450x40mm).
Here I want to introduce an LED strip with pro-fil and cover.
My question is about the light intensity to be applied in the bathroom. I already have a warm white with 3000 Kelvin; ca. 3 W/m and 350 lumens pro-bated. That was much too weak for me.
I would now rather go for 4000 Kelvin; ca. 10 W/m and 1100 lumens.
Or should I rather go for 4000 Kelvin, 13 W/m and 1550 lumens??
Thanks for the answer,
George H.* (name shortened by the editors)
We Western Europeans are sensitive to warm white light (3.000 Kelvin) as very pleasant.
We therefore tend to use a stronger warm white light rather than new-tral white light (4.000 Kelvin).
For the daily things in front of the bath-in-the-mirror are 4.000 Kelvin, on the other hand, is not a problem.
With a product like the White and Color Ambiance Light-strip (from the Philips Hue Smart Home series) there is the possibility to create different light-scenes (warm-, new-tral- and cool-white but also colored light).
I would like to install LED tube lamps vertically between the mirrors in my hairdresser’s salon. Since I have on the ceiling rather new-trale light, one looks pale in the mirror. By placing side light between the mirrors, I want to make the customer feel more comfortable. My question is, is a 500 lumen tube lam-p-en 50cm, between the mirror, or is that too little?? Thanks
Hello Gor-dona Saran,
the lumen number is sufficient, but you should make sure that you choose an LED lamp with warm white light color (about 2.700 Kelvin) and good color rendering (Ra≥80).
With kind regards
If 8 pcs 120lumen ret-roglow-lam-p are used, this value adds up to 960 or it remains 120lumen in spite of that? Is this enough to illuminate a room?
If you have several light sources, their lumen values add up. Yes, 960 lumens are sufficient to illuminate a room.
1800 lumen are how many LUX .
400 lumens are how many LUX .
Please convert for me.