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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).


Current underwater xenon strobes are difficult to use in TTL mode because the different camera makers use different proprietary TTL codes, which require special expensive TTL adapters; Backscatter has prepared a thorough Guide for these adapters (4)​, which documents how fragmented and expensive the TTL market is​.

To further emphasize the need for change, several models of the popular underwater xenon-tube Sea & Sea strobes, plus the esteemed Inon Z240, have recently been removed from the market for no stated reason
​ and the ​Sea & Sea ​YS-D2 has just now been overhauled and re-marketed.​

​This movement for change is reinforced by the advent of inexpensive and powerful white light LED COB flashes (1) and corresponding circuits (5).
As a ​proof of principle and ​matter of record, the first working LED underwater strobe was reported here in Wetpixel in 2011 (6). The speed of development in the past few years has led to many LED units integrated into one powerful COB chip with a big lumen output, ​now available at a low price (1) . Super bright underwater lights based on LED COB's, such as those from iFlash, Light & Motion whose top Sola lamp
emits 10,000 lumens, and others, foretell the advent of underwater strobes based on these LED's.

Our underwater-LED forecast may
include the speed at which solid state LED illumination is being developed, plus the imagination and ingenuity of its aficionados (4c, 5, 6), including Wetpixel contributors since 2011 (6) who continue develop simple circuits (4c, 5) to control an underwater LED flash. Not to mention commercial inventors who patent circuits to ensure that the LED flash ​emits sufficient light with the correct white balance, does not overheat, and may even provide continuous light to record video (6b).

​A​ smart underwater​ LED strobe will have an on-board microprocessor programmed to perform and give the photographer control of multiple functions​, as follows:​

Smart LED Strobe Functions.

Function Details

1. Strobe Maintenance Leak detection, battery gauge, flash readiness,

function being used, overheating

2. Spot & Focus Lamp Turns lamp off while strobe is fired

3. TTL mode
Decodes camera's TTL signal, codes appropriate TTL flashes
​​
4. M mode Manual control of LED flash duration

5.
Video Controls the LED light needed for video
recording
and other video illumination functions.​


Given ​the power of ​today's miniaturized and integrated solid state​ electronics​, the components for these functions should fit comfortably in the LED strobe's water proof case, which might be considerably smaller than current strobe cases.

As further proof of principle, two examples of LED COB
camera flashes are a) the simple circuits
​available for the LED COB chips used as flashes for cell phone cameras (6a. 6e) and b) the recently
marketed Lume Cube, an LED strobe waterproof to a depth of 24 meters​.

The LED Lume Cube ​is for use ​on ​land​ and​ gives 1500 lumens of 6000 K light, continuous or strobe​.

T​hough waterproof to a depth of 24 m​, it​ is neither recommended nor usable for UW photography. Yet it

​is a harbinger of forthcoming UW LED​ COB photo​ flashes.

 

​In light of the above, the question ​is not if, but when, the makers of UW ​lights will market LED COB based

​strobes.

REFERENCES:

1a. Cree LED for camera flash: http://www.cree.com/led-chips/media/documents/CPR3ES.pdf

1b. CREE LED COB http://www.mouser.com/ProductDetail/Cree-Inc/CXB3590-0000-000N0HCB50E/?qs=Oettwh6T2OGWS%2FWUFWYqkw%3D%3D&gclid=CjwKCAjw3_HOBRBaEiwAvLBbonYLG1keY8wDwy2leCiBVDYt-LvQnCSh_MypQ4Vt0l0Ovj5JtdlgJRoCjdoQAvD_BwE

2. Pavel Kolpakov's comments http://wetpixel.com/forums/index.php?showtopic=60039&view=findpost&p=388068

3a. Strobe problem, YSD2 http://wetpixel.com/forums/index.php?showtopic=57102

3b. and http://wetpixel.com/forums/index.php?showtopic=60161

3c. Inon Z240 problem http://wetpixel.com/forums/index.php?showtopic=60074
and http://wetpixel.com/forums/index.php?showtopic=60188

4a. Table of Flash Triggers http://www.backscatter.com/department/Lighting/product-category/Flash-Triggers

4b. http://www.backscatter.com/reviews/post/Underwater-Camera-and-Housing-TTL-Reference-Guide

4c. TTL multiplexer: https://www.google.com/search?q=strobe+ttl+circuit&safe=active&tbm=isch&source=iu&pf=m&ictx=1&fir=7_o3bKllmnzqjM%253A%252CgBmzB7O8Y3ji2M%252C_&usg=__OezmiYbZe1po5h3WwEEcOaDXFNQ%3D&sa=X&ved=0ahUKEwjKkv6n8ObWAhXCyFQKHbHeD5YQ9QEIPTAD#imgrc=9Py5d83I_65-7M:

5. DIY first LED underwater flash 2011 http://wetpixel.com/forums/index.php?showtopic=40398

6a. LED flash circuits for cell phone camera http://www.electroschematics.com/12394/camera-white-led-flash-illumination/

6b. LED circuits Hi intensity LED converter https://store.skyworksinc.com/ProductDetail/AAT1282IWOT1-Skyworks/466131/

6c. COB LED lighting, general discussion: http://forum.openag.media.mit.edu/t/cob-led-lighting/966

6d. Power source for LED photo flash, AAT1282 high-efficiency, high-current step-up 2A converter
https://store.skyworksinc.com/ProductDetail/AAT1282IWOT1-Skyworks/466131/

6e. Flash for camera phones: http://www.cnledw.com/inter/upload/20081201176530700.pdf

7. Lume Cube https://www.bhphotovideo.com/bnh/controller/home?A=details&O=&Q=&ap=y&c3api=1876%2C%7Bcreative%7D%2C%7Bkeyword%7D&gclid=Cj0KEQjwyZjKBRDu--WG9ayT_ZEBEiQApZBFuA5ehX_xjAG3tf48UXZm_KyfYxRfknrg6tMNJD1dsp0aAuCt8P8HAQ&is=REG&m=Y&sku=1192929

 

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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.

Edited by Pavel Kolpakov
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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, smarterpost-47296-0-23436100-1508471900_thumb.jpg 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/

Edited by Kraken de Mabini

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

Bill

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

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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

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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.

Edited by Pavel Kolpakov
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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

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