What is Luxi?

Luxi is a small attachment for iOS devices which works with an app to turn your device into an incident light meter. This type of light meter measures the amount of light striking a photographic subject, rather than simply measuring the subject's brightness (which is called "spot metering," and it's how the meter in your camera works). Photos taken with settings suggested by a light meter are often much more pleasing to the eye than photos taken with a simple spot meter.

What can Luxi be used for?

Beyond its primary use as an incident light meter for use in photography, Luxi can be used with special apps by third-party developers to measure light in other ways. For example, when paired with an app called Cine Meter II, Luxi can be used to measure the color temperature of a given light source. With other apps, Luxi can be used to measure a room's lighting conditions in LUX or footcandle units. See our list of compatible third party apps for more information.

My light meter app already has an incident mode. Why would I need Luxi?

It is important to capture all of the light falling on your subject. Luxi For All is designed to work just like a professional incident light meter which can capture light from a 180° angle. When using a light meter app without Luxi For All, the iPhone camera only receives light from a limited angle which means it doesn't capture all the light. This will produce readings that are both inconsistent and inaccurate. Luxi For All effectively captures and averages all the incident light.

Will Luxi work with my smartphone’s case?

Luxi For All will work with any case which is less than half an inch in thickness at the point where the phone's front-facing camera is located.

Which apps work with Luxi?

Luxi works with any light meter app that can use the front-facing camera and can be calibrated with an offset. We have tested Luxi with many of the light meter apps available for the iPhone. Please see our list of compatible applications.

Does Luxi work with flashes?

Unfortunately not. While Luxi itself has no limitations on this, light meter apps are unable to detect light coming from flashes due to smartphone / tablet hardware limitations.

With which smartphones/tablets is Luxi compatible?

Luxi For All will work with any iOS device which has a front-facing camera, including all iPhones, all iPads except for the first-generation model, and all iPods Touch with a front-facing camera.

Is it possible to measure general light levels with Luxi?

Yes, it's possible with apps which include this feature. However, we recommend using Luxi for reference purposes only.

Why do I have to calibrate the app?

We designed Luxi to be as accurate as possible. However, due to variances in the camera hardware from one phone to the next, some form of calibration must be done by the customer in order to ensure optimal accuracy. The good news is that this step should really only need to be taken once.

How do I calibrate the app?

The specific steps required for calibration depend upon which application you’re using, but the basics are pretty much the same across light meter apps. Our own Luxi app can be calibrated by completing the process below.

• Grab an 18 percent grey card (if you don't have one, they are available from any photography store, or on Amazon);

• Set your camera to aperture exposure mode, and choose spot metering;

• Set an ISO setting and an aperture setting and make sure that exposure compensation is set to zero;

• Zoom in on the grey card and make note of the shutter speed that the camera recommends;

• Compare this to what the light meter app suggests (with the Luxi-equipped iPhone sitting beside the 18 percent grey card in the same light) and use the calibration routine to fine-tune the app so that the shutter suggestion matches your camera's readings.

There may be a brief period of trial and error while you make calibration refinements, but before long your calibration will be set and you won’t have to bother with it any longer.