Can your iPhone really be a light meter?

This past February I backed my first Kickstarter project ever- the Luxi. According to James Flynn, this little iPhone accessory would change my iPhone into a light meter. And, if you have spent any time on this blog, you know I'm a HUGE fan of light meters. So for $14, I figured why not give it a try- for that money, it would be worth a shot, even if it failed. Like a lot of kickstarters, this one missed its target delivery date- May 2013 came and went. But, fortunately, they did finally deliver my adapter last week. And, as it would happen, I had a scouting and testing day already on the calendar, so what better way to test it out, then in a real work situation...?


A Little Bit About Luxi:
The Luxi Pocket Meter is a white dome that slips over the front camera of your iPhone 4/4s or iPhone 5. After slipping it over the camera, you use the Pocket Light Meter App ($0 - $4.99) to take a reading the same way you would if you were using an incident meter. You can then either take a screen grab of your phone, or you can have the app make a note for you and save that log to Dropbox for future reference. If you want to learn more, or see a demo video, check out www.luximeter.com. The adapter is now on sale for $29.95.

What I tested:
On my location scout and camera test day, I used the meter in a studio setting, a day exterior, a day interior, and then a night exterior. This represented a good range of situations (and subjects) that I frequently find myself working with in any shoot. I also decided to bring along my Sekonic 758Cine, and 478D to use as baseline comparisons. I opted not to use the spot meter function of the iPhone apps, as I have already tested that function and developed best practices for their use.

The Studio:
In my studio setup, I was lighting a Sekonic Exposure Profile Target to compare the 5D MKIII Video Raw and the Canon C100 in Log recorded to ProRes. In this highly controlled setup, both of my Sekonic meters gave me a reading of F11 4/10, while my Luxi gave me a reading of F16, a difference of 3/5 of a stop. As I had my Luxi setup to display in 1/3 increments, a reading of F13 would have been more accurate.

Sekonic Meter Readings (Studio)

Luxi Meter Reading (Studio)
[Note: 1/48 vs 1/50 doesn't make for a noticeable exposure difference in practice, but I should have set it to 1/48]

If I were shooting film, a difference of 3/5 of a stop would not bother me too much, as film is much more forgiving than digital. With digital, however, the clip point in overexposure is of paramount importance, so getting a correct reading is crucial. Fortunately, in this case, even though the reading was off, it was telling me to underexpose the image- which would have protected my highlights, and I can live with that.

(You might also like: How To Use A Light Meter)

On Location:
Funnily enough, the results in the uncontrolled environments were much more consistent between the three meters. The day exterior gave me a reading of F8 8/10 on the 758Cine, F8 6/10 on the 478D, and a F10 on the Luxi. For the day interior, I had readings of F11 3/10 (758Cine), F11 2/10 (478D), & F11 (Luxi).

Sekonic Meter Readings (Exterior Day)

Luxi Meter Reading (Exterior Day)

Unfortunately, at high ISO's and low light levels, the Luxi was again under-performing. However, I don't think that this is directly related to the Luxi, but rather a function of the limitations of the camera on the iPhone- it was never meant to take light readings. At ISO 2000 I got the following readings: F0.5 4/10 (758Cine), F0.5 5/10 (478D), and Too Dark / F1.0 (Luxi)

Sekonic Meter Readings (Night Exterior)

Luxi Meter Reading (Night Exterior)

Should You Get One?
While the Luxi and Pocket Meter app was not as accurate and flexible as my Sekonic meters were, I would still recommend getting the Luxi if you are tight on funds and cannot afford a professional light meter. I was surprised by how close the Luxi came to both of my Sekonic meters. As long as you are not doing a lot of low light shooting at high ISO's, the Luxi will get you in the ballpark that you need to be at with your exposure. And, more importantly, it should be able to help you pre-light and location scout without the camera you are shooting on.


What To Be Aware Of:
In addition to not working well in low light, there are two important issues to be aware of that may be a deal breaker for you...

• It only works without a case.
• If you are like me, you bring your phone with you everywhere, using it with a number of iPhone Apps, and you have a tendency to drop your phone. To protect this investment you have bought a robust cover, like the Tough Extreme. Unfortunately, if you plan on using the Luxi, you are going to have to completely remove your case every time you want to use it. And, for me, this is a deal breaker- for some reason or another, it is when I am on set that I drop my phone the most, so I have to keep my phone protected at all times. Even if my case were easy to remove (which it is not), do I really want to spend the extra time removing it every time I need to take a reading and then putting it back on?
• Small, Light, Easy To Lose.
• One of the greatest assets of the Luxi is that it is small, light and easy to use. Unfortunately, it is so small and light that it is easy to lose, misplace, or go unnoticed if it falls out of your pocket. There is a short lanyard that comes with it, but I'm not really sure how it is supposed to be used. If I put it around my wrist, I'm sure the plastic of the Luxi will get smashed and broken unintentionally when I'm not paying attention. And there is no way I can put it around my neck...

Luxi in its Bag, with Lanyard

Why You Should Use A Professional Meter:
If I were able to have a protective case on my iPhone and still use the Luxi, I honestly would consider using this as a replacement for my professional meters. However, the one major feature set that my professional meters have over the Luxi is adaptability. Not only can I create and display custom camera profiles for every camera I use, but I can adjust every setting with finite detail. This level of control and precision can't be matched by the Luxi (but there are apps like the Cine Meter from Adam Wilt, that show that more is certainly possible...).

So, until those two things can be overcome, I'll be sticking with my traditional light meter- at least for the time being...

Are you currently using an iPhone app for your metering needs? How has that been working out for you? Which style of meter do you prefer- app, or traditional? Why?

Until Next Time - Get Out There And Shoot!

Ryan E. Walters, Cinematographer

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