strange photo experience

[tarhoosier]

Taking photo of car today. Car was running, lights on. I stood in front of car with iphone XR and setting for single still photo. As I looked at my phone screen which displayed the camera view the headlights were strobing. I lowered the phone and the lights were on, no strobe. I raised the phone and in the screen the lights strobed for maybe 1/5th second then on for same time then strobe for 1/5th second then solid on and so forth. To my eye there was no change, just the daytime lights. What did I experience?

 

[Beefer]

LSD is awesome isn't it?

JK

My guess is the screen output (still or otherwise) only refreshes x times/second.
The car's LED's cycle as well (AC current).
So as the screen refreshes and the LED's cycle...they are not in synch...causing a strobe affect.

 

[joegr]

This is normal and seems to apply to nearly all cars with LED lighting. You can see it on the news and other TV shows from time to time. The LEDs are pulsed at high frequency as a way to regulate the current through them and to control brightness. Our eyes have persistence, so as long as the pulses are fast enough, we see it as steady light. The sensors in the cameras are much faster than our eyes, and can even make the pulsing seem worse than it is due to aliasing between the pulse rate of the LEDs and the scan rate of the camera.

 

[joegr]

...My guess is the screen output (still or otherwise) only refreshes x times/second. So as the screen refreshes...it is causing a strobe affect.

Actually, the LEDs really are strobing. It's just that our eyes are too slow to see it. The camera experiences aliasing due to it's scan rate not being exactly the pulse rate of the LEDs. This "slows down" the strobing to the point that you can see it.

 

[tarhoosier]

Short burst of strobe then burst of solid light then alternating. Same reason for each?
And thanks for the techno answer.

 

[canucklehead604]

not the post i expected when i read the title referring to photography, strange experiences, and so forth.

yeah, it's the refresh rate thing with LEDs not jiving with your camera. no biggie.

 

[joegr]

Short burst of strobe then burst of solid light then alternating. Same reason for each?
And thanks for the techno answer.

Since the camera scan rate is not synchronized to the LED pulse rate, you will get these sort of effects. It's similar to how the spokes on wagon wheels look on old TV shows. Sometimes it looks like they are going backwards and sometimes forwards. Again, that is aliasing. Also note that the pulse rate of the LEDs will change as battery/alternator voltage changes and as temperature changes. The electronics are trying to get the same light level out as electrical system voltage changes, and as temperature changes. (LEDs generally get brighter as the temperature drops.)

 

[tarhoosier]

Checking my photo roll just now and LED lights appear OFF, not illuminated though they were on in real life.
Professional auto photographers have way more to deal with than any of us can believe.

 

[joegr]

Checking my photo roll just now and LED lights appear OFF, not illuminated though they were on in real life.
Professional auto photographers have way more to deal with than any of us can believe.

What you need is a longer exposure time. I don't think that your phone allows you to do this as is, but there may be an app that you can download that will do this for you.

 

[Beefer]

If camera phone...just do multi exposure/burst. One of the the pictures will nab it correctly.

DSLR...increase exposure.

I think these crazy new phones allow for minor exposure control.

Regardless of hardware...longer exposure requires a nice steady hand...or use a uni/tripod or a mount.

Update...my 12 Pro Max has exposure adjustment (I just got it).

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