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Luxi – Incident Light Meter Attachment for iPhone ⭐⭐⭐⭐

February 21, 2013

Introduction and Perspective:

These articles are created to inform a wide audience, whether it be Photography, Digital Cameras, Lenses, Photo Editing Software, Smart Phones, Laptops, iPads, iPhones, and a variety of related products that may attach to these devices. The purpose is to inform all those interested in what is currently available, coming soon based on what is believed to be reliable sources. This is not the place for rumors, which has its own separate Category on our site.

Not that many years ago, say 1990’s getting an accurate exposure for your photos could be a risky matter because I didn’t get to see the actual image result until the prints came back from the lab. More advanced amateurs and professionals would sometimes use a hand-held incident light meter, which would measure the light shining onto the subject; the Camera’s internal exposure system measures the light reflected by the subject, and entering through the camera’s lens, known as reflected light metering.

The Luxi, an attachment to one’s iPhone simulates incident light metering by placing the LUXI clip-on over the iPhone’s Rear Camera lens. This provides an "incidence white opaque dome" which is the method of incident light-metering used by hand-held incident-light meters.

LUXI has created an iPhone App that measures "Incident Light" based readings when the LUXI is attached to the iPhone, and calculates the appropriate exposure values for taking the Picture.

The digital cameras with internal light metering, almost all have this feature these days, Measures the Light from the scene, literally the light reflected from the Subject and measured by the light comming into the camera through the lens (remember the marketing phrase "through the lens metering" which was hot new technology in the 1980’s). Over the recent 20 years the Camera’s internal light-metering systems and processors, evaluate the light from a huge variety of possible scenes, that a photographer may envision. There are settings like Spot Metering, Average Metering, and many varieties in between.

However, even with the most sophisticated processors within Professional Digital camera equipment, there are scenes that are challenging. For example, taking a picture of a Model leaning on a brick wall in the late evening, where a single street-light is shining from 30 feet away, top-side-lighting the Subject. Imaging situations like this, may "trick" the camera’s processors becuase of this unique lighting situation.

There are two primary methods to capture this image situation:

  • (1) Take a series of "bracketed" photographs; meaning, 5 "duplicate" images where the shutter speed that the Camera calculated is manually-changed, by one-f-stop, then two-f-stops higher than the Camera Metered result, then capture another two images one-f-stop, then two-f-stops lower than the Camera’s calculation, and capture one image using the cameras calculated exposure values. Many Modern Digital Cameras have a menu-bracketing-setting to take these 5 images, using the 1 then 2 over, and the, 1 then 2 under example, like Canon’s EOS 7D, EOS 5D Mark II, and the 5D Mark III, among many others.

  • (2) Use an Incident Light Meter. Taking this reading is accomplished by literally walking over to the Subject, then hold the Incident Light Meter’s White Dome Cover, up to the sublect’s face, pointing the light meter’s sensor towards the CAMERA (not the Street Light). This measures the light that is falling onto the Subject, rather than the camera measuring the light reflecting from the Subject. 99% of the time reflected light, through the lens metering is fine. But there is that 1% we are speaking about.

  • (3) The issues using multiple bracketed images, (#1) is the the Subject must be stationery, and the "smile-eyes-open" has to remain constant; Image #4 may be the best exposure, but the subject’s eyes were closed, smile not perfect… Issues with Incident Light Metering (#2) the photographer may either not have time to get over to the Subject, or the Subject is across moving traffic, water, whatever. The advantage of the indicent metering, the method preferred by most Pros, with all the shots captrured, the selection process is based on the best smile-eyes-open, as all the exposures are consistent.

Price of a quality Hand-Held Light Meter: The Sekonic used on the Kickstarter page (view Link below) costs about $250. The LUXI clip-on opaque lens, is only $20. Luxi’s companion iPhone App, which measures the light readings using the iPhone rear camera, and translates the light readings to Exposure Values in to f-stops and shutter-speed combinations, based on an ISO value you select.


Product Name: Luxi, clip on Incident Light Meter accessory to iPhone.

Rating: ⭐⭐⭐⭐ Star Rating by Jimmy

Suggested Retail Price: $20, the companion App, is a Free App Store download

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