Lumu Light Meter

Last updated September 14, 2014

Lumu light meter - a light meter for your smartphone!

Important Specifications

Diameter 24mm (0.94 inches)
Thickness 18 mm (0.78 inches)
Type Digital light meter for ambient light
Light-receiving method Incident light
Light-receptor element Silicon photo diode
Measuring range (ambient incident light, ISO 100) 0.15 – 250,000 lux (EV -4 – 20)
Repeat accuracy +/- 0.1 EV
Light receptor diffuser type Hemispherical diffuser, cardioid-type
Power source Mobile device
Requirements iOS devices (iOS6 and newer).

Lumu is a light meter for your smartphone.


On November 27, 2014 - Lumu has updated the iPhone app (now v2.0) in a big way with a new reflected light meter mode, using only the iPhone camera. There are also optimizations for iPhone 6/6+, note syncing to iCloud, a more accessible multiple measurements view, a prettier side menu and overall improvements and bug fixes. Check out Lumu in the App Store.


In this review, we'll cover an interesting piece of hardware for your smartphone - the Lumu light meter.

Lumu light meter as packaged

The Lumu company is a small team based out of .0661173,14.5320991,9z/data=!4m2!3m1!1s0x476531f5969886d1:0x400f81c823fec20">Ljubljana, Slovenia - friends, photographers, engineers, researchers, designers and explorers who have known each other for a very long time, and is comprised of Luka Mali, Marko Pirc, Benjamin Polovič, Maja Tisel, Staš Stankovič and Niko Klansek. The project itself started off on Kickstarter and not only reached its $20,000 USD funding goal on July 12, 2013... But far surpassed it at over $244,000 USD! Clearly there was demand for such a device.

The Hardware

The Lumu hardware is custom designed and built by the company itself, and is composed of over 50 individual parts, requiring ten different manufacturing processes. The design is smart, modern and surprisingly high-spec. It is purely an incident meter, using a hemispherical diffuser - as such, it does not offer reflective or spot readings. The measuring range at ISO 100 is an impressive 0.15 to 250,000 LUX (EV -4 to 20) with an accuracy of +/- 0.1 EV. This range and accuracy is better than many dedicated light meters and especially those in most cameras. Also impressive is the fact that the device functions without a battery! It converts light readings to an audio signal that is read through the headphone jack of your smartphone.

Exploded view of the Lumu hardware
It takes more than 50 parts and 10 different manufacturing processes to make one Lumu

The electronics are housed in a case milled from a solid block of aluminum, which is anodized in silver or black. The Lumu logo is engraved and paint filled, like high quality cameras and lens controls. The plastic diffuser is designed for accuracy and protects the contents.

Design drawing of the Lumu hardware
Detailed mechanical design of the Lumu body

The fact that it's an incident-only light meter shouldn't be seen as a negative. Rather, it's the most accurate way to measure light - as it falls upon your subject. It is not subject to being fooled by background brightness, tonality, color or other influences. Though it may have been nice to offer a removable diffuser to measure reflected light like some dedicated light meters.

A better alternative to reading the light in many scenes is to use an “incident” meter. Handheld incident meters read the intensity of light falling on the subject and are usually taken from the subject position. Because they are not affected by variances in subject color or reflectance, incident meters accurately record the amount of light falling on the subject. In the majority of situations, an incident reading is extremely accurate and records tones, colors, and values correctly. - Sekonic

Other nice hardware touches include a 2.2mm stand-off of the audio plug. This allows the Lumu to be used with various smartphone cases, provided they aren't too thick. In our case, literally and figuratively, it proved to be too much and needed to be removed in order to use the Lumu with our iPhone 5 during testing. Worth noting is that because of the audio jack connection, the Lumu can be easily swiveled a full 360º around for perfect aiming and reading of the smartphone screen.

Lumu light meter and Lumubag/pouch

Despite its small size, leaving the Lumu plugged into your phone all the time probably isn't something you want to do. They've thought of everything, in this case. The Lumu is provided with both a lanyard (the "Lumuneck") to wear around your neck that the Lumu plugs into - as well as a small leather pouch (the "Lumubag") that can be slipped onto your camera strap! Both are of high quality.

The Software

A custom piece of hardware is only half of the story, and being made for a smartphone - the other half is clear... The actual UI and functionality for the Lumu is entirely derived through an app that's available for iPhone (iOS 6+) platform. When you think about it, this is really smart. Instead of carrying around a separate light meter, why not use the smartphone you probably already do? Furthermore, the features can be enhanced (or changed) with a simple update of the app. Rather than buying a physical light meter, with built-in buttons, dials or knobs representing a feature set that will never change - you now have the best of both worlds.

There are currently three apps available for the Lumu hardware, all for iOS, depending on your application needs - Lumu, Lumu Video and Lumu Pinhole. It should be noted that the Lumu Pinhole app requires iOS 7+ whereas the other two only require iOS 6+. Android support was mentioned in the Kickstarter campaign, but is not yet available.

The Lumu light meter app also has some functions that you may find useful and handy. For example, you can take notes on your readings. Say for example, you're shooting in mixed light, with B&W film rated at ISO 400 and using a light yellow filter. While it won't save your settings as a preset (which would be a great feature to add), it will let you remember what influenced your exposure. You can also add things like location, what effect you were going for (e.g. high key, low key, etc.) or whatever else suits your fancy. There's an option in the settings that allows you to synchronize your notes with Dropbox, if you prefer. This feature is most useful for use with film, obviously... Giving you the equivalent of EXIF info for your frames.

Another option lets you select a custom wallpaper for the background of the app, and even blur it. Totally optional, perhaps even a bit useless - but it's a nice touch that lets you tweak the app to your liking... Because chances are, you'll be spending a lot of time looking at it!

The real meat of the Lumu app however, are the "measure light" and "photo" modes - along with settings. These can be seen here:

Lumu light meter app - settings Lumu light meter app - measure light mode Lumu light meter app - photo mode
Settings, measure light and photo mode screens

So how is it to use the app in your daily shooting? As easy as it gets, really. In "photo" mode, you are presented with three values (from top to bottom - aperture, shutter speed and ISO) and a "measure" button. You simply hit this button to take the reading, and the values above it adjust accordingly. You must select one of the three values, which the meter will adjust according to the reading - or swipe left/right to change it yourself (either way, the other values adjust accordingly). That's really about all there is to it.

The "measure light" mode is even simpler. It provides a constantly updated reading of the light level in LUX or FC (foot candles) as well as EV. In the first case, you swipe left/right to change between the units and the second case, swipe to change the ISO. Below the two readings is a "hold" button.


We compared the Lumu readings against both a dedicated Sekonic 208S light meter as well as those within various cameras, from a Leica M9 to a Fujifilm X-T1. Each time, the Lumu gave similar readings that were either a match, or very close - and often better. While the Sekonic can read incident light, camera meters can only read reflected, and are often fooled.

Lumu light meter comparison with Sekonic 208S

A feature tucked away in the settings panel of the Lumu light meter app lets you fine-tune the readings given by allowing you to select film or digital and tweak LUX/FC calibration. You can also dial in exposure correction and filter compensation. The latter is very useful if you're out shooting with a filter for B&W photography or using a polarizer. You can dial in the filter compensation and use the Lumu as normal, knowing that the readings will take the hit in light into consideration for perfect results. This is something you'd have to do mentally with most light meters!

In Practice

We found the Lumu really easy to use in practice. Installation is as easy as clicking it into your iPhone's headphone jack. Removal is just as easy. The provided neck strap and pouch are very handy when it comes time for the latter... Rather than losing it in a bag or pocket, it'll always be handy. Unfortunately, it's a bit large to leave on your phone all the time, and we'd worry about snapping it off or causing other damage anyway. Since the headphone plug/jack is round, you get the added benefit of being able to swivel the Lumu a full 360º to whatever angle suits your fancy.

One point worth noting is that on the iPhone 5/5s, the headphone jack was moved to the bottom of the phone, from the top, where it has been on all previous models. No worries! Just rotate the phone 180º and the app will rotate along with it. Of course, it doesn't work in landscape mode.

Something we found a little frustrating is the fact that in "photo" mode, light readings require you to tap the "measure" button on the screen - each time. There's no option for continuous metering, as there is in "measure light" mode. If you're moving the Lumu around a subject's face for example, it means you'll be tapping several times at least. It would be nice to have the option to toggle this on/off. Though perhaps it is this way for battery consumption reasons. We might argue that the phone is on either way if you're looking at the screen.

Speaking of the "measure light" mode, one interesting (non-photographic) use we found was to use it in comparing light bulbs... We recently upgraded from old incandescent to new LED bulbs in the studio and wanted to not only compare the old and new - but verify the claims by the manufacturer of output lumens. No problem!


The Lumu light meter is a great little gadget that will surely appeal to many photographers. In this day and age, it's almost a given that everyone will have a smartphone with them at any given time. So rather than carry an extra device (a dedicated light meter), Lumu gives you the smallest alternative option - and one that's far more accurate than plain apps lacking additional hardware.

While the price is a bit on the higher side, and the Lumu lacks more advanced features than basic readings - keep in mind that it's still a relatively new product, and new features are only an app upgrade away. We expect that more features and wider compatibility (across platforms) will come in due time. The hardware itself does what it should (and does it well) so we don't expect it to be obsolete any time soon. The packaging and provided extras with the Lumu round out the offering quite nicely - making it fun and user-friendly. You can get your Lumu at the official Lumu shop - U.S. and international.

Conclusion: We definitely recommend the Lumu and with the holidays coming up - would make a great stocking stuffer for your photography friends!

Product Videos

The Kickstarter video:

Lumu Kickstarter video

Manufacturing the Lumu:

manufacturing Lumu

Lumu light meter measuring accuracy:

Lumu light meter measuring accuracy