​​Is there a Smart Underwater LED Strobe in our future?

Is there a Smart Underwater LED Strobe in our future?

While underwater strobes have traditionally used xenon flash tubes as the source of light, white light LED COB chips are now available (1). In a recent discussion Pavel Kolpakov suggests that today it is better to build good xenon strobes than to pursue other alternatives (2) . But xenon tubes continue to give us underwater photographers a problem or two, well documented in these pages (3), so let us examine the issue a bit more. (LED: light emitting diode, COB: circuit on board​, strobe: underwater flash/strobe and/or TTL strobe, TTL: through the lens metering).

It is true that xenon flash tubes have provided great service since they were developed almost 90 years ago by Harold "Doc" Edgerton of MIT, nicknamed Papa Flash by the crew of the Calypso. But these flash tubes are made of fragile glass, require high voltage and get quite hot in order to activate the xenon's electrons into plasma; plus flash tubes tend to fail or break suddenly as experienced recently by several Wetpixel contributors (3).

Xenon tube works at high voltage, usually 330v...450 V. Such high voltage together with current 100...200A leads to huge flash energy 100...250 joules in pulse, - this is the key feature (together with super fast xenon discharge 1...5ms for getting sharp pictures) of xenon tube. Only this way we can get Guid Number (GN) =24...32 for wide-angle underwater strobes today.

By the way, xenon tube is very cheap, it costs 3 $.

LED flash energy is hundred times less than xenon at the same pulse duration, because of low voltage and small current through the LED. This is the key feature here.

Working voltage for most powerful COB LEDs is 40...50v, at current 10....20A. Using 800w COB LED, it is possible to build photo flash with GN=8 (at ISO 100). Very weak flash.

By the way, such powerful COB LED costs several hundred USD.

But people (including me) build LED strobes from time to time ...., - for interest, as experimental, for research etc.

As a fact, LED usage for underwater strobes is not effective for today, - very low power in flash, big size body, very expensive in manufacturing. They cannot compete with xenon strobes yet.

But LED technology is developing rapidly, maybe after few years we can see any good news at this field, who knows. Let's be optimists.

After I posted "Is there a Smart LED Strobe in Our Future?" I learned of the Vela One ultra-high speed strobe, based on COB LED's and using 4 AA batteries for power. The Vela One strobe emits high power flashes adjustable from one-half a millionth of a second up to 5 millionths of a second, fast and bright enough to image a high speed bullet in flight, as shown in the attached photos.

We how have LED photo strobes at both ends of the user spectrum, from the Lume Cube to take photos with a cell phone, to the Vela One to take highly specialized photos. Now we need for the strobe companies to produce an underwater LED strobe that is better, smaller, smarter and less expensive than the rather mediocre underwater strobes currently on the market, which are based on breakable glass tubes and which keep on going up in price. Underwater photographers need an LED strobe that is more versatile and powerful and cost less than the current crop of underwater strobes.

Reference:

http://www.vela.io/vela-one-high-speed-flash/

Underwater LED strobe is available on the market: http://subtronic.de/productView.php?product=Sirius

Strobe is based on 400watt COB LED. This is one of the most powerful LED strobes for today. Guide Number =4 (ISO 100 standard).

Well a GN of 4 isn't so interesting except for macro where it might be useful, but $1000 seems a bit pricey.

Bill

This is the difference between the physics of light emitting diodes and the physics of gas discharge. LED pulse power is hundred times less.

Pavel;

Do you know the rise time of the chip on board LEDs? Is it fast enough to drive at very high speeds?

thanks

Bill

Pavel;

Do you know the rise time of the chip on board LEDs? Is it fast enough to drive at very high speeds?

thanks

Bill

Many LEDs have rise time 0.1 - 50 microseconds, dependently of LED model and application. However, i saw super fast LEDs with response time 3 nanoseconds in special application, but it was a rare case. I usually rate low-power LED's response time in microseconds, for common case.

If you mean powerful LED arrays in high-current lighting applications, they can have significantly longer rise /fall time, very dependable of power source, schematic and other factors. Better measure it by oscilloscope in concrete case.

I was hoping that you (being the library for these things) could save me a few days in the lab. 50 microseconds seems reasonable but the Vela guys are claiming 5 us pulse (rise plus turn off ) which seems too fast to me. Most or our lab LEDs (in the near IR) are difficult to pulse very fast.

Bill