Lightning Strikes and Camera Sensors
CircuitHub is a second home on the web for many electrical engineers, so, naturally, we get asked electricity questions by our non-engineering friends. I found this one really interesting because I wasn't sure of the answer at first...
"If I take a picture of a lightning strike with my cell phone will it damage the camera sensor?"
...well let's figure it out, shall we?
WARNING: Math and frivolity follow. No lifeguard on duty. Swim at your own risk.
The simple answer is no.
Of course, there is some luminous intensity above which the cell sensor will die, but lightening will most likely not get there:
- Lightning only lasts about 30 micro-seconds so the absorbed energy per pixel is actually quite small
- You observe lightning from a great distance (intensity drops off at the square of the distance.
- The PRP (pulse repetition period) is extremely high compared to the pulse-width (e.g. low energy waveform)
According to the National Oceanic and Atmospheric Administration (NOAA) the average lightning bolt contains enough energy to light a 100W incandescent bulb for 3 months. That's almost a billion (777,600,000) Joules of electrical energy! However, only a small fraction of that energy is converted to optical energy (light), just like the incandescent (~3%).
Assuming you are 1km from the lightning bolt (VERY CLOSE!), the emitted optical energy is spread over the surface of a sphere.
100,000 cm in 1km
Area = 4 Pi r^2 = 125,660,000,000 cm^2
Irradiance = Energy / Area = 0.00015 Joules,optical/cm^2
Here is the human eye safety limit for collimated polarized light:
1/(2048/0.358) = 1.75 micron width of a pixel
= 1.75^2 micron^2 area of a pixel
pixel area / illumination sphere = 2.43e-19
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