We are often asked if we have any plans to design an accessory to detect lightning, a quick search on the internet will show that there are many of these devices available, but just how effective are they?
The price range of these devices is quite wide, the cheapest that we found was £25, hand-held detectors (as used by golfers) are about £250 and the professional devices installed at airfields are £2500 upwards. So, why the difference in price and is the £25 device really as good as the £2,500 one?
Lightning is a complex system, in simplistic terms, it relies on opposite charges being generated within a cloud and these charges being discharged, it is this discharge that generates the lightning which we want to photograph. The general cycle of events, once a discharge is initiated, is:
A streamer will propagate down towards earth, this is referred to as the “stepped leader”.
As the stepped leader approaches earth an opposing streamer is generated from the earth which meets the stepped leader before it reaches the earth.
The circuit is completed when the two streamers meet, this results in a return stroke which follows the path made by the stepped leader.
It is this return stroke which generates the lightning flash and the thunder.
Methods of detecting lightning
Probably the most ineffective method. At the point where the lightning strike occurs the thunder and lightning are concurrent, if we assume that we are standing 5km away from the strike, it will take about 17us for the light to reach us and about 15s for the sound which is far too long.
Light sensors for detecting lightning come in various versions, the basic sensor is a photodiode which will detect presence of light, not much use if you want to photograph during a daytime storm.
The more elaborate sensors will have either a sensitivity control, where you can adjust the trigger threshold, or a sampling system which sets the ambient light level as a reference and detects an increase above this level.
We see the visible spectrum of lightning but immediately prior to this there is an event within the infrared part of the spectrum, an infrared sensor will operate along the same lines as a light sensor but will have either an infrared filter or a photodiode optimised for this particular wavelength.
These are the professional sensors which detect the build up of the charge prior to the strike, more warning devices than detectors, they are often installed as arrays and are used at airfields and oil rigs.
So, back to the page heading “How to photograph lightning”. In some countries lightning is a common phenomenon (think of lightning chasers in America), in others it’s not so common so we don’t really want to invest a lot of money in a piece of kit which will be used twice a year (even if it means getting some great images).
Those of you with a medium wave radio (more commonly called AM) have probably noticed that during a storm you will hear loud “crackles” on the radio, these loud “crackles” are being generated by the discharge (the return stroke). If you tune the radio away from the station the “crackles” become more obvious (note. This will not work on an FM radio), they become even more apparent on long wave (do they still make radios capable of long wave reception?). Okay, set up the VersaTrigger with a microphone and place the microphone next to the radio loudspeaker, adjust the radio volume so that you can just hear the noise. Adjust the gain control of the VersaTrigger to the point where it triggers, now just back it off slightly. When a “crackle” is heard on the radio the VersaTrigger will fire your camera.
Of course, the next problem is where to point your camera. We’re working on that one ….