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There are a number of smart phone apps which use the phone's camera as a light meter. How well do these work?

The metering built into most modern cameras is very powerful and accurate, but in some cases it's nice to have a detached device. A smartphone is something I already have with me, and the app are only a few bucks, compared to $40 for a very cheap analog meter — or hundreds for a nice one.

Do these apps really work, or are they gimmicks? Can they get the same information from a scene that a real device can? Can they be used as incident-light meters without additional physical attachments like a diffuser dome? Are they accurate? How accurate, compared to the various stand-alone devices? Do the phone apps have any advantages?

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So I also want to add. If you want to use this as an incident meter then just buy a grey card and get the reflective reading from the grey card. Works like a charm :) –  user11336 Aug 27 '12 at 13:37
    
@user11336 Incident meters are aimed at the source. Your configuration describes a reflectance one. –  Stan Sep 11 '13 at 23:56
    
Didja try a comparison of the readings? How do they compare? Why would you use the smart phone reading in preference to the one in your smart camera? –  Stan Sep 12 '13 at 0:02

5 Answers 5

up vote 7 down vote accepted

Disclosure: I'm the guy behind Cine Meter and Cine Meter II, so take what I say with a grain of salt, grin.

Do these apps really work, or are they gimmicks?

They really work, within the limits of what the built-in camera allows. They may not be able to measure really dim light, for example.

Can they get the same information from a scene that a real device can?

Yes.

Can they be used as incident-light meters without additional physical attachments like a diffuser dome?

No. You either need a diffuser dome like Luxi or an add-on incident meter like Lumu

Are they accurate? How accurate, compared to the various stand-alone devices?

To within 1/10 stop (the limits of my measuring capability) if done correctly.

Many apps use the camera's own exposure setting, so can vary by nearly a stop at times from what a meter might see (smartphone cameras often "expose to the right" a bit to maximize SNR). iOS devices provide a "brightness value" in their EXIF data stream, and that value appears to track external meters pretty much exactly. Apps that use the brightness value, or that do image analysis on captured pix to compensate for the camera's ETTR behavior, should track an external meter to within a tenth of a stop.

Do the phone apps have any advantages?

  1. "The best lightmeter is the one you have with you."
  2. Cost: if you already have the phone, a metering app is a cheap add-on. If you don't have a phone, an iPod touch works fine, and it's cheaper than a standalone meter.
  3. Features: an app can add things like a false-color display or a waveform monitor to help in visualizing how the light falls on a scene and to look at contrast ratios. If they enable the front-facing camera, you can use 'em for reflected-reading "lightmeter selfies", using yourself as a model before your talent arrives. Also, when taking reflected readings, they show you exactly what the "meter" is seeing.
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I've used Pocket Light Meter for the iPhone (like dpollitt :) when using my grandfather's old Leica IIIc, a 35mm rangefinder with no light meter or automatic metering. I played around with it quite a lot, comparing its results against those of my Canon 5DmkII's metering, and found it to be very accurate. The results from the Leica bore this out too: generally (where I hadn't messed something up :) they were well exposed. So that app at least is certainly useful and by no means a gimmick.

The same won't apply to all smartphone meters though. Without straying too far into Stackoverflow's territory, a smartphone light meter's effectiveness will depend on two things:

  1. The quality of the phone's camera and firmware (i.e. does it expose well itself)
  2. The means by which the software developers can access the exposure information

On Android phones, for example, the usual method is to get the camera to take a photo then read that photo's EXIF data to determine the exposure settings. However, not all manufacturers include EXIF data in their photos (and it's easy to imagine others - especially cheap, low-end phones - might include inaccurate EXIF data), so reliability will vary between models.

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I agree that the original question is hard to answer when considering ALL phones and all applications. That is kind of a problem. –  dpollitt Aug 25 '11 at 17:35
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That wasn't a criticism of the question, by the way. It's a great question, but there's rarely a one-shape-fits-all answer for smartphones. –  Mark Whitaker Aug 25 '11 at 17:45

I use Pocket Light Meter by Nuwaste Studios. It is free in the Apple iOS App Store.

It lets me lock in my ISO, and Aperture, then it will calculate the shutter speed. I have used it against my Rangefinder and it seems to at least match up with the built in light meter from 40 years ago! I don't know how it compares to current gen DSLR light meters though.

Screenshot of the app in action:

enter image description here

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I was going to recommend that, the author talks about it here: flickr.com/groups/ishootfilm/discuss/72157624609700318/page2 –  vlad259 Aug 25 '11 at 15:55
    
Please do not accept this answer :) I was providing what little information and experience I have. But I would like to hear from others! –  dpollitt Aug 25 '11 at 15:56
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Also, I'm surprised I have a whole 3 bars of service! AT&T is terrible! –  dpollitt Aug 25 '11 at 15:57
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Obviously, it's not like using a Sekonic, but some straightforward experiments show this app works. If I left my meter behind and felt it was important to do reflective metering, I'd be comfortable with the results of this app as a starting point. But what I really use a meter for most is incident metering and that's not what this app is for. I'm impressed by what it is. –  Steve Ross Aug 27 '11 at 1:36

Cine Meter App by Adam Wilt works great.

And I believe his name is enough to believe that it really works.

This is by far the best investment of 4.99.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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For those of us who have no idea who Adam Wilt is, care to enlighten us? Can you expand on your answer just a bit: features? accuracy? what does it do differently/better than other apps? –  MikeW Mar 4 '13 at 0:40

FLitesys on windows phone gives the actual EV and indoor it says EV=5 which is plausible, and under the table it said EV=4 which is also OK, but then outside in daylight it said EV=5, too. Which would cause a nice white image. So you have to make sure you test the app in different conditions. Other problem these apps can have is if they dont give an absolute measure of exposure, but just evaluate how well exposed the test image is based on arbitrary settings. It should use this measurement together with the actual settings to give you the EV. (Exposure Value)

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