Planning the lighting for a photo or video shoot can be complicated, and the terminology used to measure light in lighting equipment can make things even more confusing. When shopping online, most lights list “lumens” or “lux” among their specifications, although sometimes “lumens” is written as “lumen flux.” You might even get confused between brightness and brightness. It’s a lot. So let’s break it all down.
One thing to note: You may have seen light bulbs whose power is measured in watts; LED bulbs often say something like “60W equivalent”. However, watts are a measure of the amount of electricity a light bulb uses, not the amount of light it emits. This data is a holdover from the days when incandescent lights were popular and used significantly more energy than today’s LED lights. However, as energy-saving lamps become more popular, using watts as a shorthand for the amount of light a bulb emits is no longer useful (it wasn’t very useful to begin with). This is why you will see terms like lumens or lux on professional lighting equipment.
What are Lumens?
The first term you should know is lumens. The amount of visible light a source emits is called luminous flux and lumens are the unit of measurement of that raw output. You can think of this in the same way that “distance” refers to the distance between two places, while “km” is the unit used to measure that distance. Lumens are in kilometers in that analogy.
This can be a bit confusing because companies will list “luminescent flux” without naming the unit of measurement. For example, one in Our favorite lights for professional video capturethe Godox SL-60W, lists its lumen output as 4,500 in its description. Using our metaphor above, this is like saying “Distance: 4,500” without listing the unit to which that number refers.
That said, although they are not interchangeable, if you see “lumen flux” listed on a product spec sheet, it is probably referring to lumens. However, it’s important to double-check that you’re comparing comparable figures when buying lights from different manufacturers.
You can also refer to this metric as “luminance,” which is another, less common way to refer to a light source’s output. And, like “luminescent flux,” it is a general term for a concept, not a unit of measurement. However, this is different from Brightness, refers to reflected light, not light coming directly from a source. And yes, it’s confusing.
What is Lux?
How much light the source emits is only part of the story. After all, the sun radiates enough energy to melt… basically anything. Luckily, the sun has a good sense of personal space and is far enough away from Earth to not destroy us all. For similar, less dire reasons, calculating your light source distance will affect the type of lighting you need.
Lux is defined as one lumen per square meter, although the math is possible become difficult because we are dealing with surface area in three-dimensional space. Don’t worry, you don’t need to sweat too much. Most professional lighting systems will simply list their output in lux (as well as lumens) and specify distance. For example, Aputure Amaran P60X rated at 5,070 lux at 1 meter.
This means that a subject 1 meter away from a light source will effectively perceive more than 5,000 lumens of light falling on them. If they are further away, less light from the source will hit them and so the subject will appear dimmer. This is helpful when buying lights because you may not need the brightest light in the world. You just need to make sure the subject is a suitable distance from the light source.
Inverse square law (and other math)
Finding the right distance for a light source is not necessarily intuitive because of two main factors: First inverse square law, one of the oddities of the universe that we have to deal with. To put it very simply (mathematicians, please don’t scold me), every time you double distance between subject and light source, you four times How much light is needed to illuminate them the same way?
In other words, that means that every time you move twice as far away from a light source, only 1/4 of the light from that source will hit your subject. So use Amaran P60X For the example above, if it is rated as 5,070 lux at a distance of 1 meter then the subject will experience approximately 1,267 lux at a distance of 2 meters. Some lights will specify their brightness at shorter distances, such as 0.5 metres, this is important to ensure you compare equivalent specifications when looking at lights from different manufacturers. different.
