Using a Light Meter for Photography
Even though many modern cameras come with an in-built light meter, for a truly accurate light reading you should be using a separate device. Whether shooting pictures or video, on location or in a studio, these light measuring instruments can save you time whilst improving the quality of your work.
As you might expect, the conversation around light and how it works is huge. We’re not going to go into meticulous detail about the science behind lumen meters, as that can often lead to more confusion for the everyday user. If you do want a more in-depth study, you can find sources online that can offer this. For more information on the science behind light, try this article from OMEGA Engineering. Instead, this product guide is mainly going to be aimed at photographers new to using lumen meters, although if you do have a bit more experience then don’t worry - you may find some useful information you didn’t know!
What is a light meter?
Firstly, let’s begin with a brief introduction to lumen meters to ensure that we’re all on the same page. A lumen meter, or light meter or lux meter as they are also known (we might interchange between all three in this text), is a small handheld light intensity measurement device.
These instruments have a wide variety of applications and would be found in industries such as agriculture and horticulture, biological science and theatre performance. For this article, we’ll be looking at how they are used in photography and cinematography to ensure that an environment is lit appropriately. Crucially, this will decide whether your image is exposed correctly or not - so it’s important to get it right.
When we use the term exposed, we mean how an image is lit. Sometimes, photographers would want their image to match how the human eye would view the photographed subject, although this isn’t always the case. For greater creative control, a camera operator may want to change the exposure of the image to suit their tastes or needs, hence why a lumen meter is just so important. There are other ways of exposing your shot, especially with modern cameras that may come with a histogram or zebra pattern function, although lumen meters are unquestionably the most accurate.
Some lumen meters will take the lux reading and then convert it into your desired exposure format, or in other words tell you what shutter speed and aperture to shoot at. Others, such as the instruments supplied by The Measurement Shop, will only tell you the lux reading instead without converting it into information that is usable by your camera. This isn’t a problem though, as you can find plenty of conversion tables online to reference. For more information on how to use these conversion tables, please see the ‘how to use a light meter in photography’ section below.
How do you measure light?
When looking at light meters and lumen meters, it’s always best to have a bit of knowledge about light and how it works before you begin. Let’s explain one of the most confusing aspects of measuring light - the units. Lumens are the units that are used to measure the brightness of light. They are different to other units of light measurement such as lux, candelas, footcandles or watts (you can forget about footcandles and watts for now) so don’t get them mixed up!
On the subject of candelas and lux, they are both actually linked to the lumen in a way. One candela is roughly equivalent to the light emitted from one lit candle. One lumen is defined as being equal to one candela per steradian (a cone shaped area that starts from the source of the light). Think of this figure as the actual amount of light that is coming from your light source.
Once you have found out how to measure lumens, what you really want to determine when measuring light is how many lumens fall on a surface area - this figure is known as a luminous flux (or lux for short). It is defined as being one lumen per square meter. Although a bit complicated at first, hopefully this gives you a background into what it is you are measuring when using a lumen meter.
Why should I use a light meter?
As mentioned, most cameras today come with a built-in light meter which may have various types of metering modes. So why would you need to you use a separate digital light meter? The answer is simple; nothing will be as accurate as an instrument specifically designed for the job. If you want the finest level of accuracy in setting your exposure, then you need to be using a light meter of some kind.
It must also be said that not everyone uses a modern camera! Many photographers choose to shoot on vintage models without the ability of easily setting shutter speed and aperture. In the case of film cameras, unless you’re very experienced in shooting in this format, you’ll struggle to know the correct exposure settings to use. Afterall, you don’t have the luxury of taking a test shot and checking the exposure on a digital screen! Since film is expensive, you probably don’t want to be wasting it by taking any duds, so it will pay to purchase a lumen meter.
They can also be very handy in an environment where the light is changing all the time. In this instance, a digital light meter will allow you to take a reading and quickly set your exposure and start shooting immediately. Alternatively, many lumen meters come with a peak hold function which will allow you to keep track on the highest light reading in a given environment.
Another very useful time to use a lumen meter is when location scouting. If you’re searching for the perfect place for a photoshoot or filmset, it pays to know what the lighting conditions are like long before you arrive. You can then relay this information to the rest of the camera crew so that everyone is clued up and ready to go.
What light meter should I buy?
The Measurement Shop have a range of light meters and lumen meters for sale that can be used for photography applications. You can buy lumen meters from us that feature a whole host of different features, so it’s best to know what you want from your device before you purchase. To find the best analogue light meter for you, take a look at some of our products below:
REED R1930 COMPACT LIGHT METER
REED R1930 is a compact lumen meter that is easy to use and durable. This instrument is capable of taking a lux and Footcandle (Fc) measurements, so you won’t have to convert between the two. REED also offer over 150 testing and measuring instruments and have become a truly reliable company to purchase from.
SP SAUTER LIGHT MEASURING INSTRUMENT
Sauter are well known for making high quality measuring equipment and the SP lumen meter is no exception. This device contains a peak hold function that can capture data peaks as well as a data hold function to freeze the current measurement. This makes it a useful tool if you’re planning to shoot in an environment where the light levels can change quickly.
SO SAUTER LIGHT MEASURING INSTRUMENT
Another Sauter device, the SO lumen meter features a photo sensor that is connected to the display via wire for maximum maneuverability. When you buy lumen meters, it’s always good to know whether they’re cut out for the job. Luckily, the SO boasts a rugged and robust design that has been constructed to withstand testing environments. It also has a track feature that means you can continuously record variable environmental conditions.
How to use a light meter in photography
So, you’ve done all your research and you’ve gone out and purchased a light meter - what’s next? Now, you use it! Firstly, it’s important to note that all light meters are different, so this is only going to be a general guide on how to use them. It is recommended that you read up on how to use your specific instrument.
If you think about what it is you want your light meter to do, you will begin to understand how it should be used. Essentially, you want to know how a light source affects the subject that you will be shooting. With this in mind, it’s best to position the device facing the camera lens, just in front of your subject. In the image below you can see how this would be done if you were shooting a person. It’s important to make sure that your device is taking in a full range of light and dark information. To do this, simply make sure that your light meter isn’t facing directly into a light, or equally that is isn’t in too much in the shadows. From here, it’s as simple as reading the number given on the display of your device.
In a studio environment, you can play with the light meter in order to change your exposure value. To get a darker and moodier image, simply move your light meter so that it is facing your main light. This basically means that the device will disregard the shadowy side of the face, thus giving a higher lux value which in turn will give a higher exposure value.
For light meters that only give a lux value, it’s important you know how to convert this figure into a usable exposure. As mentioned above, there are tables available online so here’s a quick guide on how to use them.
For each lux reading you will get a corresponding EV (exposure value) reading. But what is exposure value? It is basically a figure that is made up from your shutter speed and your aperture. To ensure that we only focus on these two factors, we do not take into account the ISO reading and therefore the chart is only applicable when your camera is set to ISO 100. Once you’ve found your EV reading, you can use the table to determine your shutter speed and aperture. Obviously, there will be more than one option, so it’s down to you to choose which shutter speed and aperture is right for you.
For our full list of light meters and lumen meters, please visit our light meters page.