FTechX

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5. Getting the heat out

LEDs are more efficient than both halogen and HID lamps but, like halogens and HIDs, LEDs do not convert all their input power into light power.  Some of the input is wasted as heat.  Dealing with this unusable heat is an engineering concern for all lighting systems. 


In the halogen and HID systems much of this heat leaves the lamp with the visible light radiation.  The area to be illuminated is both illuminated and heated!  This is not the case for LEDs.  Most of the wasted energy stays in the LED raising the LED temperature.  This is not good for the LED.  It shortens the LED life and reduces the LED efficiency and light output.  Because the LED is so small, only a few square millimeters, it takes only a small amount of wasted energy to raise the LED temperature by quite a lot.  Although LEDs provide more lumens per watt than any other lamps, approximately 70% of the LED input power becomes wasted heat


A 2000 lumen video light, built of 100 lumen/watt LEDs will have an input power of 20 watts which results in about 14 watts of heat (70% x 20 watts).  To prevent LED degradation, these 14 watts
must be taken out of the LED and moved somewhere else. 



Typically, this is done by connecting the LED in a dive light with a series of thermal conductors to the water  in which we are diving.  As diagrammed to the right, the heat flows out of the LED package (LED) , thru a conductive adhesive layer (A) to a transfer conductor (B) and then to a heat sink (C) which must be thermally well-connected to the water. 



Ideally, only high conductivity thermal materials should be used.  The thermal conductivities of a few materials are shown in the table below. 




The material system used in the FTechX Classic 700  is shown in green in the table above, where higher numbers are better.  We use Solder (A) to connect to the LED, use Copper (B) (not Aluminum) to conduct the heat away from the LED and into the Aluminum (C) case of the videolight.  We use the entire case of the FTechX Classic 700  to provide the maximum thermal connection to the surrounding water.


The FTechX Classic 700  is a "no compromise" thermal design.  This design enables FTechXto use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 

 

 

4. Do you really need a 50,000 hour LED lamp?

What does 50,000 hours mean?

  • If you work from nine to five, without lunch or coffee breaks, five days a week for one year with only a two week vacation, it would take you 25 years to add up 50,000 hours of work!
  • If you dive three times each day with a one hour video session on each dive for six days per week all year with no vacation, it would take you 53 years to add up 50,000 hours of video dive sessions!

The 50,000 hours LED lamp life is the average life of a large number of LEDs.  Some last longer and some die sooner.  What you care about is that your videolight does NOT fail while you are shooting the fantastic scene that you want to capture, and that it does not need to be replaced until you decide to! 

A 50,000 hour LED lamp is MUCH LESS LIKELY to fail at 1000 hours than a 2000 hour halogen lamp or a 1000 hour HID lamp.

You will probably trade in your 50,000 hour LED videolight before you get 50,000 hours of use BUT while you have it you will get higher reliability, and more light and/or more burn-time than any other lamp.




3. Are more LEDs better?

 

All too often sellers of LED lights emphasize the number of LEDs in the light. Should the prospective purchaser buy the light with the most LEDs?  Are 19-LED lights better than 12- or 4- or 3-LED (Note 1) lights? 

Most ads for low cost, imported flashlights tout the number of LEDs that they have and imply that the more LEDs, the better.  While it may be true for low cost flashlights, it is not true for quality-engineered videolights.  

 

One reason some manufacturers use a lot of LEDs is that often a lot of lower cost LEDs are less expensive than a few really good LEDs.

All LEDs are limited in their wattage and lumens-per-watt.  Higher wattage LEDs are more expensive because they dissipate heat better, thereby permitting higher wattages.  Higher lumen-per-watt LEDs are more expensive because only some of the LEDs manufactured reach high lumens-per-watt - most fall short. 

 

By using more LEDs, the designer can spread the required wattage over a larger number of LEDs, so that each LED is below its' maximum wattage.   Adding even more LEDs to increase the wattage and get more total lumen output from low lumen-per-watt, low wattage LEDs will drain the battery faster and reduce battery run-time.

 

As discussed below in  " 2. Why LEDs?," the higher LED performance achieved in the laboratory, quickly becomes available in commercial LEDs. These newer, high performance commercial LEDs cost more but are worth it.  By using state-of-the-art, high wattage LEDs,  designs with FEWER LEDs can be brighter and more efficient than designs with the older, lower cost LEDs.

 

 



Note 1   19-LED: Light & Motion Sunray 2000; 12-LED; Light & Motion Sunray 1000; 4-LED: FTechX Classic 700; and 3-LED: Nocturnal Lights SLX 800i

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2. Why LEDs?

 

compromise" thermal design.  This design enables to use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 

 

compromise" thermal design.  This design enables to use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 

 

compromise" thermal design.  This design enables to use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 

 

compromise" thermal design.  This design enables to use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 
compromise" thermal design.  This design enables to use four x 100+ lumen/watt LEDs to achieve 700+ lumens without compromising the LED lifetime due to heating of the LEDs. 


An underwater videographer wants the most light for the least input power. 

Lamp energy performance or "efficacy" is the amount of output light per unit of input power. Efficacy is measured in lumens per watt.  The figure below shows the efficacy of various lamp technologies.

 

 


The Virginia Energy Savers Handbook, 2005

http://www.dmme.virginia.gov/DE/ConsumerInfo/HandbookLighting.pdf

 

There is an efficacy range for each lamp technology.  Often there is an optimum size or input power that maximizes the lamp efficacy.  For example, this figure illustrates that compact fluorescent lamps have smaller peak efficacies than tubular fluorescent lamps, even though they all are based on the same physics.  Similarly, although metal halide or HID lamps can have efficacies well over 100 lumens/watt, the smaller HID lamps frequently used in scuba lights have efficacies at the lower end of the range.

In 2005, LEDs were not practical for lighting, however, since then the international quest for energy-efficient lighting is driving LED technology to new heights.  The lighting market far exceeds the underwater video-photo light market but we divers benefit tremendously. LED progress is dramatic and shows no evidence of slowing. 

 

The next figure shows the US Department of Energy LED Improvement Roadmap, and the commercial and laboratory performance achieved so far.

Demonstrating the Next Wave of LED Chips and Packaging Improvements    

http://www1.eere.energy.gov/buildings/ssl/printable versions/sf09 materials.html

161 lumen/watt and 249 lumen/watt data

http://www.ledsmagazine.com/news/5/11/20

 http://compoundsemiconductor.net/cws/article/news/37614

 

 

 

For advanced underwater videographers,

LEDs provide more lumens per watt

than

any other available lamp technology.

 

LED progress is exciting for underwater videography!

Laboratory demonstrated 160 lumen/watt LEDs are

2X better than HIDs

4X better than Halogens!

 


In less than two years, 140 lumen/watt LEDs should be in production!

With 140 lumen/watt LEDs and 8 AA batteries

divers could have

2000 lumens for > 90 minutes

 

In our next installment -more about LED issues for an underwater videolight.

 

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1. A Few Simple Light Facts

 

 

To get a bright light we first need a lamp  that converts electric power to light output.  Second, we need a battery to store the electricity that provides power to the lamp.  In addition, we need optics like lenses or reflectors to capture and control the light, circuits and switches to change and control the light intensity, and underwater-suitable cases and mounting brackets.

 

Light for seeing, taking videos and photos is measured in lumens.  The power that the lamp needs is measured in watts.  A good lamp outputs lots of lumens for each watt that it uses.  For example, a really good halogen light gives 20­ lumens of light output for each watt of electrical input.


           


So if we want to get 400 lumens of light for a one hour night dive, we could use a 20 watt halogen lamp and a battery that could output 20 watts for one hour.  

 

Battery capacity is measured in units of watt-hours or equivalently battery-volts x  battery-ampere-hours.  A good AA-sized NiMH (Nickel Metal Halide) rechargeable battery has a voltage of 1.2 volts and an ampere-hour rating of 2.5 ampere-hours.  Thus, a battery pack with 8 of these cells could provide 8 x 1.2 x 2.5 = 24 watt-hours and should be okay for a one hour night dive.  A smaller battery pack containing only 6 of these cells would provide only 18 watt-hours, and the light would dim before the end of the one hour dive.

 

LEDs or Light Emitting Diodes are exciting new products  because a good commercial LED gives about 80 lumens of light output for each watt of electrical input.  

   

The 6-cell battery pack might provide 640 lumens of light for over two hours – an hour of dark swim-thru videos during the day as well as the night photo-dive.

 

 

A 20 watt Halogen lamp outputs about 400 lumens

 

A 20 watt lamp needs a 20 watt-hour  battery

to stay lit for 1 hour.


A 6-cell NiMH battery pack has a capacity of about 18 watt-hours
Not quite enough for 1 hour !
 

 

 

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