Failed! Lux Meter Apps

How and when did you calibrate you "professional" Lux meter ?

Thanks

"Some people, though, are too lazy to get their own lux meter"

Please, don't beat around the bush. Say what you think.

"the iOS apps are stronger in terms of usability and overall indoor measurements. "

I am not sure we can conclude that from the informations given. It could also be because of the phones sensor version. For example it may be very plausible that devices running either Android or IOS have different sensors depending on the model or year of manufacture. Thus, a Galaxy S4 could be even more accurate than an Iphone.

I understand that the pro LT300 meter is the more accurate device, but an app that could be calibrated with a decent sensor would be much acessible to many professionals

For Android, there is an app called "Android Sensor" where you can check the harware version and resolution. I hope that one day we will get better sensors in order to decrease the gap between apps and pro devices.

I didn't see listed anywhere what Android phone you used... some actually have a light sensor (for automatic brightness adjustment of the screen) rather than using the camera, and in addition to "lux meter" apps, there are several Android apps that will simply display the output of the various sensors in the phone (lux, temp, pressure, accelerometers, gravity sensors, magnetic sensor/compass, etc.)

Now that said, I don't think the light sensors tend to have very good resolution (ie. very rough measurements), and I don't know that they're generally calibrated in lux as all they need to do is match the screen brightness to a pre-defined sensor output. And on my HTC, it doesn't output any numbers below 10 lux, so not really useful for this application...

Matt,

The Android phone used in the test was an HTC One X, Android version 4.1.1. Also, thank you for the added information! Do you know what android apps would display phone sensors?

Here's my experience from over 30 years in this industry, not all in the camera side....

Rule 1 There is always time and money to replace cameras that are not providing a suitable image. Not enough time and money to investigate in advance.

Rule 2 It always works in conference room demos and PowerPoint presentations.

Rule 3 The hardest thing to manage is a customers expectations after the sale when not managed before the sale.

Good article: DON’T ‘PHONE IT IN’: WHY SMARTPHONES ARE POOR SUBSTITUTES FOR LIGHT METERS, key quotes:

Light meters generally include three key photometric (i.e. light measurement) aspects: a photodiode, a luminosity function filter, and a cosine correcting lens.

• The photodiode converts the whole wide range of visible colors and invisible ultraviolet (UV) and infrared (IR) wavelengths into an analog signal for the light meter to measure and report.
• The luminosity function filter moderates or blocks wavelengths based on how important they are to human photopic vision.
• The cosine correcting lens further moderates the light received by the sensor based on how humans perceive diffuse (i.e. Lambertian) surfaces.

To render images well, the camera minimizes any barriers between the environment and the image sensor. As a rule, cellphones prefer transparent screens. The glass screen minimally distorts the light coming-in, but it does not offer a cosine correction. Some light meter app proponents have tried to solve the problem with a snap-on cosine correcting lens; however, the exact photometric performance is hard to verify.

The glass on cameras tends to have a specular surface, which generally redirects low angle light, while high angle light tends to pass through to the sensor easily. Even though we wish to discount low-angle light sources, we cannot ignore it all together. Furthermore, any low angle light that does pass through the glass, may not even reach the camera due to the relatively small camera angle of view (generally 50° to 70°) typical of cell phones.