Photography is all about light. It’s about capturing light, manipulating light, and interpreting light. Today’s digital cameras use advanced algorithms and sensors to properly measure light and then record what you’re seeing with your eyes. But cameras weren’t always so smart and sophisticated, and with more and more people exploring film photography with vintage cameras, light meters are once again becoming required tools for those serious about photography. A light meter measures the light in an environment and helps you set your camera for the proper exposure on your image. This is doubly important in film photography, where it’s much harder to correct a poorly exposed image (too dark or too light) after the fact.
That’s where the Lumu comes in. There are two types of light meters in photography. The $149 Lumu, which plugs into your smartphone’s headphone jack, can measure incidental light, the light that falls right on your subject or what you want to be exposed properly in your photo. But a camera is only capable of measuring the light reflected back into it, another step removed from the light directly on your subject. Exposing an image using incidental light is generally considered to be a more accurate method, which is why you’ll still see professional portrait photographers and cinematographers with light meters dangling around their necks.
A circular device roughly the size of an American quarter, the Lumu is much smaller than a traditional light meter, and makes use of the smartphone you’re already carrying around. There’s a special light sensing chip under a plastic diffusion dome on the Lumu, and an app to provide an exposure recommendation based on the measured light. In effect, the Lumu is using today’s technology to make it easier to take pictures with yesterday’s methods.
The Lumu comes in black or silver, is made of aluminum, and requires no batteries of its own. Included in the square tin with the Lumu is a neck strap and leather pouch to store the device when it’s not in use. (The tin can also be repurposed as a film storage container, as it’s just tall enough to accommodate a 35mm roll of film standing up.)
There are two apps that work alongside the Lumu: a standard light-metering app and one designed specifically for pinhole photography. The light metering app offers a variety of settings and can display exposure recommendations in full stop, half stop, or third stop steps. Just as with a traditional light meter, I can set my chosen ISO and aperture, and the app will recommend the right shutter speed for my camera based on the current lighting conditions. Or I can lock my shutter speed and have the app recommend apertures. The app also provides a Dropbox-syncable notes section for jotting down the exposure settings for each frame in a roll of film, which can be referred to later on after the pictures have been developed.
the Lumu is capable of measuring the light directly falling on your subject
I tested the Lumu and its app on an iPhone 5S (there is an Android app available in the Play Store, but it only works on a limited number of phones and in my experience it was slower and less accurate than the iOS version), shooting pictures with my Fujifilm X100s, which has a very good reflective metering system. I also compared it to a Sekonic L-358, a traditional handheld light meter that originally retailed for a few hundred dollars.
Getting an exposure setting with the Lumu is quick and effortless
The Lumu proved to be quite accurate in its readings, recommending exposures that were within a third of a stop of what my camera was telling me and what the more expensive and complicated Sekonic recommended. The Lumu snaps into the iPhone’s headphone jack firmly and even works when the phone is in a case. Its metering recommendations are closest to the "spot" metering settings on a digital camera, and assist when trying to expose for a very specific area. The one area that the Lumu falls behind full size meters is in measuring flash — it just isn’t designed to work with flash photography.
I took the Lumu and my camera outside this past weekend to take pictures of my family at the park. The lighting conditions were fairly difficult: the sun kept ducking behind the clouds and then reappearing, requiring me to adjust exposure settings on my camera for nearly every shot. The Lumu’s instant readings gave me accurate recommendations, whether my daughter was playing in bright sunlight or sitting in the shade. If I was shooting with slide film, it would have been invaluable in getting the picture correct in the camera, since fixing poorly exposed slides after the fact is a herculean task. With my digital camera, the Lumu was more or less a second confirmation that the in-camera meter was accurate.
At $149, the Lumu isn’t a cheap, throwaway accessory. If you shoot with a digital camera, you probably don’t need it, as today’s cameras have excellent metering systems already built in to them. But if you’re exploring the world of analog photography, and you’re using a vintage camera with a limited reflective meter (or no meter at all), the Lumu makes smart use of the phone you’re already carrying without the higher cost and bulk of a traditional light meter.