Hands up anyone who knows what a light meter is? You at the back… speak up… No, it’s not a way to tell how much electricity you use to illuminate your home. Fine, I’ll tell you: it’s what we used to use to measure light and set the exposure on our cameras, back before they were so good at doing it themselves.
Oddly enough, this weekend I found myself in need of one. And then what do I see in my inbox? The Lumu, a light meter for the iPhone.
These days cameras take a look at the scene before them and run the numbers. They make a good guess that the bright blob is the sun, the pink blobs are people, the blue strip is the sky and so on. Then they set the aperture, shutter speed and ISO accordingly, resulting in almost perfect pictures almost every time.
In the olden days we used something like a Lumu, which is a light meter that plugs into the headphone jack of your iPhone and works with a companion app to measure light levels. The little lollipop-shaped dongle contains a super-sensitive meter which can detect light from 0.15 – 250,000 lux. In photographic terms that’s EV –4 to EV 20. In other words, it can see in the dark.
There are two ways to measure light: Incident and reflected. Reflected measures the light that the subject reflects back at the camera, and it is easy to fool. The meter assumes that your scene’s mixture of light and shadow averages out to a standard mid gray. If it doesn’t (and no scene ever really does) then the reading is off. This is why older cameras would render both snowscapes and black cellars as gray.
Incidence metering measures the light falling on the subject, It’s way more accurate, because it can’t be fooled by white or dark subjects. And the Lumu measures incident light.
Why bother? Well, with a modern digital camera you shouldn’t Just snap a picture, eyeball it and twist the exposure compensation dial to, uh, compensate. But with film, you need to get it right the first time. That’s where the high-tech Lumu comes in.
The little aluminum button can be kept in its beautiful leather carrying case, or hung around your neck like a pretty cool medallion. When you need to measure some light, plug it into your iPhone, fire up the companion app and put it all in front of your subject. Right in front of it, and facing back at the camera. Take a reading and you’re done.
The Lumu is — as is the way with all these cool little gadgets — seeking funding on Kickstarter. You’ll need to pitch in $99 to get one.