Starlight cams and lux rating.

[Cam_curious]

I have looked at the various Dahua starlight cams and they range from 0.002 lux to 0.08 lux.
Obviously a lower lux value is better. I got this chart from WikiPedia;

Illuminance (lux) Surfaces illuminated by
0.0001 Moonless, overcast night sky (starlight)[3]
0.002 Moonless clear night sky with airglow[3]
0.05–0.3 Full moon on a clear night[4]
3.4 Dark limit of civil twilight under a clear sky[5]
20–50 Public areas with dark surroundings[6]
50 Family living room lights (Australia, 1998)[7]
80 Office building hallway/toilet lighting[8][9]
100 Very dark overcast day[3]
150 Train station platforms[10]
320–500 Office lighting[7][11][12][13]
400 Sunrise or sunset on a clear day.
1000 Overcast day;[3] typical TV studio lighting
10,000–25,000 Full daylight (not direct sun)[3]
32,000–100,000 Direct sunlight

I am interested in a camera to look into the woods at the back of my house.
There are no street lights around, it is completely dark. I don't want to use IR illumination
because (I assume) that the close trees would be illuminated brightly thereby preventing
seeing any further into the woods.

Given this it seems that the lower the lux the better but how far to to go?
At what point is there no real advantage?

Pete.

 

[john-ipvm]

Don't trust lux ratings, literally. We did a post explaining that here Don't Trust Lux Ratings

The net/net is every manufacturer gets to pick their own lux ratings so it's quite arbitrary how those ratings relate to performance. We've seen cameras with comparably 'poor' lux ratings stand out and others with 'great' lux ratings be terrible.

Also, even if a manufacturer claims 0.1 lux (which is not that low for specs) in real life lux meter measured 0.1 lux scene, the video quality is almost always poor.

Related, do you have a lux meter? If you do (and it's good enough to accurately measure in sub 1 lux) worth doing a reading so you can get a sense how dark. If you do and you measure ~1 lux, most 'super' low light cameras will be good enough but if it's less (and it can easily get to 0.1 lux if you have no ambient light, lots of even super low lux cameras will still have problems delivering a quality image.

 

[tangent]

The lux ratings are most useful when comparing within the same brand. Though even then there's variation in shutter speed, so overall usefulness is quite limited.

 

[Cam_curious]

I notice that the N28BL7Z has a lux rating of 0.002 at 3 FPS and a 0.01 lux rating at 30 FPS.
That makes sense to me, a longer light integrating time giving more sensitivity. Does this
feature really work in the real world?

What are really good cameras for a really dark scene without using IR illumination?

Pete.

 

[bigredfish]

I notice that the N28BL7Z has a lux rating of 0.002 at 3 FPS and a 0.01 lux rating at 30 FPS.
That makes sense to me, a longer light integrating time giving more sensitivity. Does this
feature really work in the real world?

Interesting... do we think this applies to most all cameras? Lower FPS>marginally better lux rating..?

 

[fenderman]

Interesting... do we think this applies to most all cameras? Lower FPS>marginally better lux rating..?

no...the lux ratings are not expressed relative to the fps, but rather the exposure...1/3 vs 1/30....when you lower the exposure to 1/3 your max fps can only be 3....and your video will look like a complete blur if there is any movement...

 

[Cam_curious]

Isn't exposure just the inverse of frames per second? Isn't 1/3 second exposure just 3 FPS?

Pete.

 

[bigredfish]

gotcha. Thx

 

[fenderman]

Isn't exposure just the inverse of frames per second? Isn't 1/3 second exposure just 3 FPS?

Pete.

no, for example you can set the camera to 1/30 exposure but 15 fps...
regardless, the only way they are achieving the higher lux rating is by increasing the exposure, which in the real world will result in motion blur....it is still an exceptionally good low light camera...as others have said, ignore the rating..

 

[tangent]

Isn't exposure just the inverse of frames per second? Isn't 1/3 second exposure just 3 FPS?

Pete.

FPS is more a matter of how the video is encoded. If you set the "shutter" long, you'd effectively end up with a number of identical / nearly identical frames.