Quick review: the Lumu light meter

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Every serious photographer has found themselves needing a light meter at some point in their careers – usually an incident one, because most cameras have very good built in reflected spot meters anyway these days. An incident meter is one that measures the amount of light actually falling on your subject; it is of course not always usable simply because you may not be able to go up to your subject to take a reading. But remembering to carry it, or charge it, or how to work it between infrequent uses probably means you don’t use it at all. And if you use an older film camera without meter, I’m sure it’s pretty obvious how a small, unobtrusive one might be useful. Today’s quick review is of the little blob that attaches to a smartphone in the images above – yes, that’s a light meter, and perhaps the most unobtrusive of them all.

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The Lumu has two parts – the measurement diode, which comes with a small leather pouch and neck lanyard, and the app – which turns your phone into a light meter. The little gizmo itself plugs into the headphone jack, drawing power from the jack, and using it to run its circuits. A photodiode then sends a reading back to the app which translates it into a meter reading. By tapping on the various segments in the display, you can set aperture/ shutter/ ISO or any combination of the three. There’s also a cine version which will show you shutter angle instead. It’s pretty simple, accurate (at least compared to the spread of other cameras I use) and works as advertised. I haven’t shot any available light portraiture with it yet (I suspect that and video are the most pertinent immediate applications) but I did find it useful when dealing with some tricky mixed lighting situations on the street which my test camera wasn’t so happy with at the time (the recently reviewed Leica X 113) and whose subjects were too dynamic for the spot meter.

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I think there’d be two modifications to make this even more useful, though: firstly, through software only – have the app take only the highest light reading within say 10 seconds, and display only that: you could use this as a flash meter. Activate the Lumu, pop the flash, and voila, perfect incident exposure. I could see myself using this quite a lot. Secondly, use of an RGB photodiode (or diodes) would enable color metering – no more need for grey cards, a Kelvin temperature readout would ensure perfect white balance every time. Perhaps in a future version…

In the meantime, if you shoot film manually, or portraiture, or available light still life, or challenging light street conditions – I think this is a pretty handy little thing to have in a pocket…MT

The Lumu is available here.


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  1. Hi Ming! After reading your review I ordered the Lumu light-meter. I like how small and convenient it is, but there are few things that I can’t figure out. There is no manual of any kind included, or online tutorial…I still cant figure out how to calibrate it, how to take average reading, or why the white line on the highlighted value changes when taking a reading, and what does it mean. I’ve been trying to contact Lumu support with those questions and have not received an answer yet! This is my first light-meter, maybe Lumu is not for beginners…?

    I dont know if Lumu Labs sent you their product with the intention to promote it with your review, but if the devise is not for newbies, I think that it should be mentioned as well as the fact that there is no tutorial or manual of any kind for it.


    • It doesn’t need a manual. You plug it in, open the app, tap on the value you want to change, hit meter and the app does the rest. It always displays an averaged value because that’s what an incident meter does…

  2. Hmm….useful…

    Re: grey card/colour profiler…just have x-rite make an iphone case…then you would always have one with you!

  3. Obviously I’m missing something here. What does this give you that you don’t already get with an ExpoDisc? I use mine for incident light metering and perfect white balance (they’re certified and hand calibrated at point of manufacture).

    • Ever tried using one of those with a view camera or meterless Hasselblad? 😉

      • Thanks for the ‘winky’ emoticon Ming. Without that, I’d have felt sheepish at missing the obvious, instead of smiling because I missed the obvious. To be fair, I thought ‘blads came with a meter, given their retail price. And I was sure you had to be wearing a beard and an anorak before they’d sell you a view camera. 🙂

  4. Interesting stuff. I’ve only seen light meters that put a dome on the iPhone camera, but prior to iOS8 the camera API was quite limited (and so was the hardware), so I have been skeptical about their ability to quickly produce accurate measurements (iOS8 introduces a a number of new functions, but I don’t know yet if they would help in light metering). Having separate hardware is thus a much more appealing idea for getting good measurements and not requiring batteries is very nice.

    That said, I have a few gripes based on reading the review. The first is lack of flash measurement, which is the most important use of a light meter in still photography. The other is that with my dedicated meter, I just need to take it out and press the metering button, while with the Lumu, I would need to plug the device in (or keep it plugged if the phone fits my pocket with it), unlock the phone (and I need a lock code…), start the app if not already at the front and then I can make a measurement. In the grand scheme of things the delay is not a big issue, but it’s nonetheless annoying. The final thing is the price, it’s kind of expensive particularly without a flash meter. And I really don’t see any need for the leather case 🙂

    • There’s one other issue your comment brings up: if the hardware changes, the algorithm of the software using the camera for measurements has to change, too; otherwise we’re going to get readings that are slightly off. Perhaps not so critical for raw exposures, but enough to throw color/temp measurements off. At least with a hardware solution you know it’s consistently the same…

      I agree though: lack of a flash meter is the biggest gotcha. And the most easily solvable one, too…

      As for speed – if you’re using an incident meter, you’ve got to go up to your subject, which generally means the kind of shoot that’s a bit slower; I haven’t found it to be an issue yet.

      • The future compatibility aspect is a good point; my lightmeter is from the 80’s, it still works flawlessly. A lightmeter connected to an iPhone is not an integrated unit anymore, so to offset the compatibility risk there need to be other compelling reasons to use the iPhone-based meter. I’m on the fence here — if it was a lot cheaper then I could live with the lack of flash and future obsoletion.

        The speed issue would really require me to use the device to be sure, now I’m just speculating. But walking to the subject I can observe the subject, pressing buttons is distracting.

  5. Erling Maartmann-Moe says:

    Agree, bought it on Kickstarter. Simple and useful.

  6. Having tried several of the light meter apps, I’ve settled for iZoner (http://j.mp/i-zoner). Though it is not an incident meter and though it has a clunky-looking interface, it is filled with really useful functions, such as spot meter, colour meter, hi-lo meter etc. It really deserves more attention than it gets.

  7. Michael Matthews says:

    Thanks for the review. I had been interested in the Lumu but thought it best to wait until any initial flurry of interest had died off. Now that I see it meets your standards it looks even better. Their website says the current model is for iOS 6 and later. Rats! I dwell far behind the curve.

  8. “Secondly, use of an RGB photodiode (or diodes) would enable color metering – no more need for grey cards, a Kelvin temperature readout would ensure perfect white balance every time.”
    I just happened to finnish reviewing the amazing Sekonic C500 color meter and had this conversation with the marketing rep- why can’t this technology be ported to smartphones. It can, but the sensor and processor are huge in a colorimitry.
    So that cute little white ball will not cut it.
    Where on the right track though. In fact, my thought is to build this into future prosumer cameras or make them logical bolt-ons somehow.
    ——-M.El-Darwish for GSQmag.com

    • The processing could be outboard to the iPhone app, and the sensor could be a small compact camera one. We just need a K temp value to the nearest 100-200 K or so; surely that can’t be that demanding…

      • Ming. Talk to Sekonic. they claim the tricolor sensor isn’t any smaller than what’s on the C500 meter so it may be a waiting game. Nearest 100-200k is very tight tolerance, so what would you pay for the accessory, $500 ? I think not.
        Truth is, I used the meter as a calibration /reference tool for tests of a WB Gizmo that I invented.
        No need for me to own it. Besides… the tool we ultimately need is NOT an incident meter but a spot meter, which I believe should be feesible via a smartphone camera 🙂
        That would permit scene sampling from the shooting camera’s POV.

        • Actually, there are instances where you need both spot and incident – if it’s just spot, a live view histogram is even better because it takes into account the camera’s native tonal response.

          For an accurate WB/color meter with flash meter? Given I do shoot a lot of product, yes, $500 seems reasonable actually. But not if I’ve got to carry significant separate device (or devices), which would tax an already overloaded carry on bag…

          • My thought is that the Solo Indie shooter would scout a scene and want to sample distant light sources, walls and the subject without having to trek around . Mixed color temps being the nightmare scenario. The camera WB shortcut is to sample the entire scene with mixed color temps calibrating the camera to average the compensation, which typically results in flat dull color. A finessed option is to sample key light sources in the scene and light the subject separately and the scene sampling will allow for a targeted camera WB calibration. If a camera profile can be input that’s fine but it really doesn’t matter since most cameras leave the factory to crunch all manual WB sampling to zero color 🙂

            • Solo Indie shooter? You’ve lost me there. I’m ‘working-pro-who-cares-about-accurate-metering-and-color-in-fixed-scenario-(but not necessarily always controlled lighting)’.

  9. plevyadophy says:

    Here’s a similar product to consider, which seems a little better thought out ( especially when they release the universal clip-on version which will work with phones other than the iPhone and a variety of phone cases ): http://www.esdevices.com/products/luxi

    • $29.00 ?? No battery, no electronic connection at all…Much more robust design – If it functioned as well.
      No cool neck lanyard? Perhaps not as pretty, but more elegant.
      Ming, do you think such a design could compete with an external diode design such as the one you tested or is the ‘simplicity’ of the design simply too limiting to function at the same performance level?

      • Depends on whether the iPhone’s front camera has an adequate working range or not, and if sensitivity/tonal response is linear. The Lumu works down to pretty darn low light levels, under which the iPhone camera gives you a black nothing. It’s more likely you’d need a meter under these situations that Sunny 16…

  10. Apart from the fact you are tied to an iDevice with limited battery, somewhat questionable reliablilty (what if it decides to fritz that day, or you have it stolen, or you’ve broken the screen) and iOS requirements, this seems like a good idea. After trying a few legacy attached devices along with my iPhone I decided as a semi-pro (or pro) where redundancy is paramount, piggy-backing a necessary device on to a different, altering ecosystem is a risk in and of itself. Even if the attached app software is decent, an iOS update could completely screw that up.
    The only way around this would be to have a dedicated iPhone for the light meter purpose (or photographic purposes let’s say). And that grew tiring pretty fast for me when using an iPhone 4 as an intervalometer or timelapse device.
    At 148EU I would suggest an actual dedicated light meter (for admittedly a bit more cash) would do the job better, with less risk.

    • Then again, as I understand it Ming you rarely do paid work with film (as is probably true for most??) so redundancy isn’t such an issue, as opposed to ease of use and portability.

    • Err…all of those things hold true for a separate meter, too. And frankly my cameras tend to be less reliable than my phone…

    • Frans Richard says:

      I have a dedicated light meter, a Sekonik L-758D. Bought it when I followed a photography course. I think it cost me 600-700 Euros. It can do all sorts of interesting measuremenst, including incident flash and very fine spot metering. It is a lot bigger than an iPhone, more the size of a serious compact camera, definitely not pocketable. You need to carry it in its case because it is easy to damage. The operation is so complex I keep forgetting how it works. The last time I wanted to use it the battery (non rechargeable CR-123A, not cheap either) was dead. It’s been gathering dust for years now.
      So what I’m trying to say is, I think you really need to be sure you’re going to be using one of these things a lot if you go for a dedicated one.
      To me the Lumu seems like a better idea for a photographer that needs an incident meter on occasion. A lot easier to carry, easier to use, no unexpected dead batteries and a lot cheaper. The design seems reasonably future proof for an iPhone user. In contrast, the Luxi mentioned by another poster only fits certain iPhone models, and only without a case on them.
      Too bad the Lumu doesn’t do flash.

  11. Ryan Hastings says:

    It would be nice if this worked for android devices too. Good write up though. Thank you.

    • I believe it does? The app was available when Wesley tried it on his phone.

      • Seems not really ever or anymore:

        “Is Lumu compatible with my phone?
        Lumu works on all iOS devices. The Lumu app requires iOS6 or newer and the Pinhole app requires iOS7.”

        “NO LONGER SUPPORTED BY LUMU LABS I contacted Lumu Labs directly asking about support for Android devices and this is their response: “Lumu supports only limited number of Android devices, namely Samsung Galaxy Note 2, Samsung Galaxy S4 and HTC One, as was released on Kickstarter page. These devices have to run Android 4.1+. Since fragmentation with Android phones is really broad and the question of Lumu support is HW not SW in nature, we discontinued development for other devices.” There is no guarantee that this will work on newer devices, but it works on my LG G3 which isn’t listed as a supported device.”

        Hard to interpret that response. Android OS fragmentation is not really an issue anymore. No more than iOS. They could easily make a supported app for Android and simply state “The Lumu app requires 4.1+ or newer.”. I suppose they are talking about HW variability as there is a lot more HW options in Android, not OS fragmentation.

    • Works with my Android devices. Bought one off Kickstarter and been serving me well for the past 6 months, although I mostly relied on in-camera metering

  12. marcuskoreanus says:

    The portability looks very good but the price is a bit steep for an iPhone attachment. I’m interested in a light meter but I think I’ll look for a used one with flash capability, etc. Of course, they’re not cheap either . . . .

    • No, it seems none of them are. I agree the price is cheap, but it’s still competitive with other options – and much smaller. I would imagine flash metering is an easy function to add in an app update. Weight optimization is definitely important these days with increasingly strict airlines though…

  13. Ming, have you tried any of the iPhone light meter apps that use the built in camera? They get pretty good reviews too, and are surprisingly accurate for what they are!

    • Yes, but they’re *reflected* light meters, not incident – not the same thing at all…

      • Václav Brodec says:

        Hi! I believe that some Android apps can employ the built in sensor for LCD brightness regulation as incident light meter. Unfortunately my phone lacks this one, so I have no idea how accurate it is.

        • We’d also need to put something over the sensor to average it to middle grey, but yes, I don’t see why that wouldn’t work providing the sensor has the appropriate working sensitivity range, and isn’t too recessed.

  14. Great! I am interested in this gadget, but couldn’t find a review anywhere. It looks like it is worth it, especially considering the dimensions.

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