stability of 'sunny 16'

[tjwspm]

What I can't figure out is that alleged Smartphone reading on the previous post. With Minolta and Pentax real spot meters, 14-1/2 EV is just a stop and a half above a typical sunny day midtone reading.

That's easy to understand. EV 13 is about 35% as bright as EV 14.5, so if you have 14.5 directly against the sun and EV 13 against the reflections, this means that 35% of the sunlight is reflected. It is said that about 30% is the average reflection in the landscape (averaged from fresh snow 80-90% to grass 25% to fresh asphalt 4%). So it fits.

 

[DREW WILEY]

I admit I don't know how various cell phone cameras either think or don't think. If this particular case is true, then not only is it not a spot reading, but a very questionable averaging if the sun is in fact in the frame - which would totally overwhelm the rest of the reading. But those gadgets are so absurdly prone to flare and so forth, that it makes little difference to me personally. I'll never take pictures with them unless it's a burglar's vehicle or something like that.

 

[BrianShaw]

I admit I don't know how various cell phone cameras either think or don't think. If this particular case is true, then not only is it not a spot reading, but a very questionable averaging if the sun is in fact in the frame - which would totally overwhelm the rest of the reading. But those gadgets are so absurdly prone to flare and so forth, that it makes little difference to me personally. I'll never take pictures with them unless it's a burglar's vehicle or something like that.

Not only is a cell phone metering app not spot, but it isn't incident either.

 

[Chan Tran]

Not only is a cell phone metering app not spot, but it isn't incident either.

I agree that is not sport nor incident but the readout in Lux is confusing. Only incident measurement should the readout be in Lux. With reflected measurement it should be Cd/m²

 

[BrianShaw]

Not only is a cell phone metering app not spot, but it isn't incident either.

My profound apologies for stating a fact when, in fact, it is likely incorrect. A Google-search indicated that a few apps indeed can do incident light measurement as well as spot metering. Similarly, there are apps that do the essence of spot metering, Either/both may be simulated in some sort of way and what I read appears to have been validated against stand-alone meters.

 

[khh]

My profound apologies for stating a fact when, in fact, it is likely incorrect. A Google-search indicated that a few apps indeed can do incident light measurement as well as spot metering. Similarly, there are apps that do the essence of spot metering, Either/both may be simulated in some sort of way and what I read appears to have been validated against stand-alone meters.

The incident meter mode often use the dedicated ambient light sensor most decent phones these day have. These sensors are essentially miniturized incident light meters that give a light reading in lux and quite fit for purpose, but of course they're not intended or calibrated for critical photography purposes.

 

[Chan Tran]

The incident meter mode often use the dedicated ambient light sensor most decent phones these day have. These sensors are essentially miniturized incident light meters that give a light reading in lux and quite fit for purpose, but of course they're not intended or calibrated for critical photography purposes.

For photographic purposes an accuracy of about +/- 25% is OK. Imagine if your ruler or thermometer or you voltmeter is that much off.

 

[tjwspm]

Midsummer noon 2025

Here are my current measurements taken with a calibrated lux meter today. Cloudless deep blue sky. We don't often have that on this particular day.

Aachen, Germany, June 21, 2025, 12 noon, 160 m above sea level, alignment of the measuring dome towards the sun: 98600 lux, EV 15.3

 

[wiltw]

Not only is a cell phone metering app not spot, but it isn't incident either.

Nor is it particularly accurate!

Today I measured an 18% gray card under diffuse indoor lighting

1. a Minolta Spotmeter F... ISO 250, 1/30 f/2
2. a Motorola Edge 2023 smartphone with Light Meter app v3.0-2025-04... ISO 250 1/10 f/2
3. a Motorola Z smartphone with Camera Meter app v3.0-2023-04... ISO 250 1/15 f/2

...BTW the Minolta Spotmeter F gives the same readings as a Canon 7DII metering the same gray card and resulting in an digital exposure registering in the middle of the histogram.

 

[Chan Tran]

Nor is it particularly accurate!

Today I measured an 18% gray card under diffuse indoor lighting

1. a Minolta Spotmeter F... ISO 250, 1/30 f/2
2. a Motorola Edge 2023 smartphone with Light Meter app v3.0-2025-04... ISO 250 1/10 f/2
3. a Motorola Z smartphone with Camera Meter app v3.0-2023-04... ISO 250 1/15 f/2

...BTW the Minolta Spotmeter F gives the same readings as a Canon 7DII metering the same gray card and resulting in an digital exposure registering in the middle of the histogram.

Which means the phone reads 1 stop too low. I wonder with a different phone the same model do you have different readings? Using the Light Meter App and my Samsung Galaxy S23 it read EV 12.3 when my Minolta meter reads 13.6.

 

[chuckroast]

I admit I don't know how various cell phone cameras either think or don't think. If this particular case is true, then not only is it not a spot reading, but a very questionable averaging if the sun is in fact in the frame - which would totally overwhelm the rest of the reading. But those gadgets are so absurdly prone to flare and so forth, that it makes little difference to me personally. I'll never take pictures with them unless it's a burglar's vehicle or something like that.

I used the compensation setting on my cell phone metering app to make it agree with a known good lightmeter. The app tracks fairly well, albeit not over as wide a range of light as a "real" meter.

I have done this with all my meters for years, using my Pentax Digital spot meter as the reference system. The Pentax may be off, I don't know, but everything is off the same amount and thus leads to good repeatability. The only issue is that some of my older analog meters like Luna Pros show some non-linearity at the ends of their range.

 

[BrianShaw]

Does anyone know the angle-of-view for a mobile phone light meter app? I suspect that it is greater than 30 degrees based on limited use. Also, any idea of the pattern?

 

[Craig]

Does anyone know the angle-of-view for a mobile phone light meter app? I suspect that it is greater than 30 degrees based on limited use. Also, any idea of the pattern?

I think it's whatever the camera on the phone is. Most are quite wide angle, the camera on my iphone is equal to a 28mm on 135 format.

I have not tried zooming in to change the angle of view and seeing what the exposure reading does, but I expect that if you excluded sky for example, the reading should chnage.

 

[wiltw]

Which means the phone reads 1 stop too low. I wonder with a different phone the same model do you have different readings? Using the Light Meter App and my Samsung Galaxy S23 it read EV 12.3 when my Minolta meter reads 13.6.

I surmise that two different units of the same model would have identical readings.
My test certainly shows that two different years from the same manjfacturer are not assurance of 'same reading'.

 

[wiltw]

I think it's whatever the camera on the phone is. Most are quite wide angle, the camera on my iphone is equal to a 28mm on 135 format.

I have not tried zooming in to change the angle of view and seeing what the exposure reading does, but I expect that if you excluded sky for example, the reading should chnage.

Reasonable thing to conclude, by my own Motorola Edge 2023 camera has a default camera angle of view which is WIDER than the area seen by the Light Meter app.
The Light Meter app area displayed is narrower than the area displayed by the default camera lens AOV.

 

[RalphLambrecht]

More like 0.0167, so that would round up to 0.02. Still probably not enough to notice in the shadows.

Yeah, that qualifies for infinitesimal influence.

 

[tjwspm]

Yeah, that qualifies for infinitesimal influence.

Absolutely. The three measurements I took over the last eight weeks and posted in this thread are only half a f-stop apart. They were taken at different times of day, different seasons, and more than 1,000 km apart.

The only thing they have in common is that it was always blue skies and sunshine, as it should be with sunny 16.