Luxi Turns Your iPhone into a Professional Light Meter

Luxi for iPhone5/Images by Author

Luxi for iPhone5/Images by Author

For years, professional photographers and filmmakers have been using light meters to tell them just how bright or dim the scene being recorded is but these handheld meters are rather pricey. The Luxi system from Extrasensory Devices is a diffusion dome attachment that clips on your iPhone and provides a very good, very affordable alternative to those expensive professional meters.

Light in a scene can be measured by how much luminance is falling on a particular subject or in a certain area. This is known as ambient or incident light. Light can also be measured as it reflects from a subject or object in a scene and this value is measured as reflected light. Either is an acceptable way to measure the light in a scene you wish to photograph and each has its distinct advantages.

Photography is all about light and the images we make with our cameras/devices/whatever interpret how that light plays on the scene we are photographing. How the device records that light is usually chosen through a reading given from a metering system of some sort that has been told to see the overall scene in a light shade of gray.

While the world is not made of that 18 percent gray that most cameras or devices have been told to adjust for this certainly is a very good starting point. Technology is to the point where 18 percent gray shade of light will yield a nice image for posting or reproduction of some sort but there are times when we do not want to trust the metering system.

The benefit to using a light meter or the Luxi system is that an in-camera metering system will adjust for reflected light and this can sometimes be fooled when there is something overly dark or overly bright in the scene and this will lead to an image that will be too dark or too light. Also, the light meter only benefits those who have a camera or device that allows for manual override of pre-programmed settings. The added benefit of the digital age is that one can see the recorded image immediately to be certain of proper exposure or recording of the light in a scene.


The Luxi device is a small plastic clip-on attachment available for iPhone4 or iPhone 5 but the phone has to be out of any case. The white light-diffusing dome covers the device’s front camera and incident light coming through the diffuser dome is read by that front camera and sent to an app installed on the iPhone. Luxi offers a free app available in the iOS app store. When launched, the app tells the device to switch to that front camera to take light readings instantly. These readings are displayed on the screen and show up as both light (EV) values and camera settings.

The camera settings are adjustable and allow the user to predetermine two of three settings: aperture, shutter speed or ISO, and Luxi will give the recommended setting for the one not selected. The light reading should be taken with the phone near the portion of the scene most important and the dome pointed toward the position of the camera.


For more advanced photographers Luxi offers a spot metering function on its app that uses the rear camera of the device and you can tap on the area of the screen image to tell where you want Luxi to measure that reflected light.

The price of the Luxi device is $29.95 USD and as I mentioned, the Luxi App is free. Unfortunately the system cannot be used to measure the light from flash units but for a handheld light meter this is quite the bargain and is very accurate. I would recommend this system to any serious photographer who loves photography in available light or via constant light sources such as floodlamps.

Luxi from Extrasensory Devices available online at

MSRP: $29.95 USD

What I Like: Accurate, handheld light meter; competes with professional units at a tenth of the price

What Needs Improvement: No flash metering available

Source: Manufacturer supplied review sample

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About the Author

David Goodspeed
David was editor of AutoworldToday at Today Newspapers in the Dallas suburbs until its closing in 2009. He was also webmaster and photographer/videographer. He got started doing photography for the newspaper while working as a firefighter/paramedic in one of his towns, and began working for the newspaper group full-time in 1992. David entered automotive journalism in 1998 and became AutoworldToday editor in 2002. On the average, he drives some 100 new vehicles each year. He enjoys the great outdoors and as an avid fly fisherman, as is his spouse Tish. He especially enjoys nature photography and is inspired by the works of Ansel Adams.