How to use your smartphone as a Light Meter for photography and for shooting videos

Light Meters are incredible devices that help us measure light. In the world of photography or videography this helps us in getting proper exposure. That is why they’re also called Exposure Meters. You’ll see them in the bags of every professional photographer because they help get optimum exposure. You will see them in the kits of every film-shooter because they are also used to maintain the ‘light’ between individual shots within a scene. In fact Light Meters are also used by architects, construction workers & interior designers, to get information about light installations in homes. A lot of companies make really good Exposure Meters, my personal favourite being Sekonic.

Being professional tools, Exposure Meters don’t come cheap, at least the good ones don’t. The Sekonic L-858D-U SPEEDMASTER Light Meter featured above retails for $599 or roughly ₹ 43,760 when straight-converted, in fact on the day of me writing this feature it was ₹ 52,550 on Amazon India. This is not to say that cheaper options don’t exist. Even our DSLR & Mirrorless Cameras have Light Meters in them, that’s how they get Auto-Mode right or display EV values. But most of us vLoggers or casual film-makers don’t ever feel the need to buy a dedicated Light Meter. Even I simply rent one when needed on client shoots.

But I’m going to show you how you can use your smartphone as a Light Meter. It can be any Android phone or any iPhone. It should just be latest enough to support installation of the following two apps.

• Android : Light Meter – Free
• iOS : Lumu Light Meter

Multiple other apps on both platforms will work, but I have used these two apps for a long time without running into problems or glitches. And mostly they have enabled me to get fairly accurate exposures with minimal needs to correct in post-production. Both these apps offer paid versions with more features. Lumu in fact is a physical accessory, it’s the world’s smallest lightning-port based Exposure Meter. You can buy different versions of Lumu & they will unlock different features accordingly. But the free versions of both apps can turn the camera sensor of your phone in to a Light Meter as well. And depending on the phone you have, the results can be impressively accurate. Full disclosure, I only use the free version on both apps on my phones, & I use an iPhone SE 2020 & a OnePlus 7Pro.

The process is pretty simple & very alike on both the apps.

Android	iOS / iPadOS
Select Camera Meter from the list of available options	Enter Spot Metering mode.
You can tap anywhere in the camera interface to select & meter your subject.	Once you enter the interface, find settings on the top right side. You will need to set the Maximum Lens Aperture value because you can’t set this manually in the app. Set this as per the aperture value based on the lens that you will be using.
On the bottom you will see four rectangles representing: f/ – Aperture ISO – ISO Value sec – Shutter Speed ev – Exposure Value	Red text on top will tell you if you are underexposed. You can tap this to set Photo Mode or Video Mode. Video Mode will let you set values for Frame Per Second as well as ISO & Shutter Speed. I use Video Mode because this lets me set lighting to my need, because I always shoot at 24fps & always set the shutter speed to 1/48.
These four boxes are either pale red or pale blue in colour.	Tap on POINT, which will make the app zoom-in on your scene. Use this to target your subject.
You can tap on a blue box & change its value. The red box values are calculated by the app. This means if you are using the app to take photos, you can long press the shutter speed box to turn it red. set values for everything else & let the app calculate ideal shutter speed for you. Or if you’re shooting videos, you can long tap on ISO & then manipulate lighting to get your camera’s Native ISO, by entering your desired values for the other two parameters.	Set the values depending on the mode you wish to use.
Depending on what you want to use the app for, Enter the aperture value you are using of the lens. Enter the shutter speed at which you want to shoot. Enter the ISO at which you want to shoot.	The red text on top will change to white & will read Video Spot Metering or Photo Spot Metering when your subject is optimally exposed.
The app will read out the optimum settings for you.	Since this app will try to suggest you aperture values if you over-expose, or just tell you in red text when you under-expose, your goal should be to either adjust lighting or shutter speed or ISO if you are using this for photography. And adjust lighting if you are filming a video. Because I suggest you try to get your ISO to match your camera’s Native ISO.
You can use these readings to manipulate the settings of your camera to get a good idea for optimum exposure. As a side-read, you can read up on the various acceptable values of EV depending on various general real life situations.	As a side-read, you can read up on the various acceptable values of EV depending on various general real life situations.
Android	iOS / iPadOS

To help you further, I’ve linked below the video in which I’ve detailed how to use Light Meter – Free on my Android phone & how to use Lumu Light Meter on my iPhone. I use both apps simultaneously to set values for my Blackmagic Production Camera 4K. I set fixed parameters on both apps & then get these apps to help me adjust my lighting to get good exposure.