Designing and Building a LED Fixture - Page 26
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Old 12-24-2010, 02:34 PM   #376
Min
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Thanks! the tanks is probably about 3 months old or so, just now got the lights done, since they almost took 1 months to ship from china.
my plants were struggling much, but seems they like new lights much better.
i will have to set some hours for the lights, as those are not dimmable.
IMO i would rather have fewer lights and run them full power then have x2 more lights and run them %50.
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Old 01-23-2011, 06:19 PM   #377
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I built another LED light, described here, http://www.plantedtank.net/forums/di...llon-tank.html This uses cheap EBay LEDs.
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Old 02-09-2011, 09:57 PM   #378
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Quote:
Originally Posted by artemm View Post
60cm long x 30 cm wide x 45 cm deep
that's
23" long x 12" wide x 18" deep




Oh not so true. Depend on the area of the heatsink, thermal resistance, ambient temperature. This all needs to be calculated.
Let's see, just for laughs, 24 leds at 0.4A with Vf of about 3. That's
0.4x3=1.2W per led, 29W per system. A big heatsink with a lot of fins can easily dissipate that much heat. I had NVIDIA 7700GTS passive cooled
video card wich dissipated around 120W of heat in closed space. Of course, there was air flow in the case and there were 2 heat pipes, the the space was tight and air flow is was not free. So, just a heat sink with nothingh above can feed the ambient air 30W for sure. Have you notice fans in your LED display?


However, you gave me an idea which i would not do Pass water to an external filter through the heatsunk to collect the heat. Then it will cool while in the filter and on it's way back and will rise the water temperature a bit, so one can save on the aquarium heater power. Neat, huh?
Last semester I took my first stab at a formal research paper as a part of my measurements and instrumentation class for mechanical engineering. I ran a thermal torcher test on a cree xp-g (IIRC). Recorded temp from the back of a 20mm star MCPCB (note: No extraneous heat sink) using a DS18B20 sensor and an Arduino. Used some math (from themal resistance, power dissapated, and ambient temps) to convert the MCPCB temp to junction temp. The power dissapated in the LED was controlled and varied with the Arduino via PWM.

At room temp and no airflow I was supprised to find that the junction temp just barely eclipsed the critical maximum recommened value of 150 Celsius at the maximum current of 1A. Meaning that, for all powers tested less than full power, the LED would not overheat. Yes it would get very hot which presents its own issues, but not to the point of damaging the junction. I did record junction temperatures greater than the maximum allowable duing the full 1 Amp test, but just barely, possibely within the resolution of my equipment at that temp. I bought 4 LEDs thinking I would need to burn at least one out to find the failure power (with no heatsink), but I was infact unable to destroy even one LED.

Comments:
A heat sink should be thought of as a way to keep the casing temperature down (so you won't burn yourself or your house).

In the discussion above the LED had acess to a constant temperature thermal reservoir (air in the room). However if it were enclosed, the ambient temperature may increase by 20 degrees causing a corrosponding increase in the junction temperature of 20 degrees.

Just thought I would share.

Last edited by Arctangent; 02-10-2011 at 01:04 AM..
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Old 02-09-2011, 11:11 PM   #379
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I love it when a skilled researcher posts useful information. Thank You!

I use the wayback machine to pull old threads from the days when grad students were the only ones who had access to UseNet areas. There is a lot of solid research behind many of today's "taken for granted" small miracles.
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Old 02-10-2011, 11:47 AM   #380
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im all for diy and im not trying to burst anyones bubble but a light fixture is something probably not worth the risk IMHO. if something did go wrong and there were damages to your home etc good luck trying to collect from your home owners insurance without a ul listing on your fixture. im a master electrician and could build any diy light from parts around the shop but the savings from a diy isnt worth the risk you take again. you can do everything right, perfect craftmanship etc but say the driver is faulty from the manufacture through no fault of your own and causes damages. ive seen t5 ballasts literally explode and blow themselves apart. again, im not lecturing anyone and most of the diy lights ive seen are well built. but there is a risk.
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Old 02-10-2011, 04:31 PM   #381
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Quote:
Originally Posted by Delgriffth View Post
im all for diy and im not trying to burst anyones bubble but a light fixture is something probably not worth the risk IMHO. if something did go wrong and there were damages to your home etc good luck trying to collect from your home owners insurance without a ul listing on your fixture. im a master electrician and could build any diy light from parts around the shop but the savings from a diy isnt worth the risk you take again. you can do everything right, perfect craftmanship etc but say the driver is faulty from the manufacture through no fault of your own and causes damages. ive seen t5 ballasts literally explode and blow themselves apart. again, im not lecturing anyone and most of the diy lights ive seen are well built. but there is a risk.
I crawled out of bed this morning - almost stubbed a toe, could have fallen and hit my head.
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Old 02-10-2011, 10:13 PM   #382
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I think you're in the wrong forum.

Quote:
Originally Posted by Delgriffth View Post
im all for diy and im not trying to burst anyones bubble but a light fixture is something probably not worth the risk IMHO. if something did go wrong and there were damages to your home etc good luck trying to collect from your home owners insurance without a ul listing on your fixture. im a master electrician and could build any diy light from parts around the shop but the savings from a diy isnt worth the risk you take again. you can do everything right, perfect craftmanship etc but say the driver is faulty from the manufacture through no fault of your own and causes damages. ive seen t5 ballasts literally explode and blow themselves apart. again, im not lecturing anyone and most of the diy lights ive seen are well built. but there is a risk.
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Old 02-10-2011, 11:16 PM   #383
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haha..nah im in the right forum and my opinion is just as welcome as yours. ive read how hoppy built his light and it looks fine to me. probably built better then anything you could buy off the shelf. but as someone who repairs lights daily ive seen what happens when they fail. now anything can fail at anytime as hoppy implied in his post and i know that. if your diy stand collapses youll have a big mess. if your diy co2 fails youll have dead fish or an algae bloom. but if your diy light fails your f'ed. good luck.
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Old 02-23-2011, 08:36 PM   #384
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Quote:
Originally Posted by Arctangent View Post
Last semester I took my first stab at a formal research paper as a part of my measurements and instrumentation class for mechanical engineering. I ran a thermal torcher test on a cree xp-g (IIRC). Recorded temp from the back of a 20mm star MCPCB (note: No extraneous heat sink) using a DS18B20 sensor and an Arduino. Used some math (from themal resistance, power dissapated, and ambient temps) to convert the MCPCB temp to junction temp. The power dissapated in the LED was controlled and varied with the Arduino via PWM.

At room temp and no airflow I was supprised to find that the junction temp just barely eclipsed the critical maximum recommened value of 150 Celsius at the maximum current of 1A. Meaning that, for all powers tested less than full power, the LED would not overheat. Yes it would get very hot which presents its own issues, but not to the point of damaging the junction. I did record junction temperatures greater than the maximum allowable duing the full 1 Amp test, but just barely, possibely within the resolution of my equipment at that temp. I bought 4 LEDs thinking I would need to burn at least one out to find the failure power (with no heatsink), but I was infact unable to destroy even one LED.

Comments:
A heat sink should be thought of as a way to keep the casing temperature down (so you won't burn yourself or your house).

In the discussion above the LED had acess to a constant temperature thermal reservoir (air in the room). However if it were enclosed, the ambient temperature may increase by 20 degrees causing a corrosponding increase in the junction temperature of 20 degrees.

Just thought I would share.
i love this! all this time i was truly thinking this way, but could not find any proof. the heatsinks are over rated just for company profits. i never heard of LED burn out due to overheating.

as a renegade example my DYI led lights running full power at 1050ma for about 3 months now on 36" by 1 1/2" aluminum strip and its ok.
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Old 02-23-2011, 08:40 PM   #385
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Quote:
Originally Posted by Delgriffth View Post
haha..nah im in the right forum and my opinion is just as welcome as yours. ive read how hoppy built his light and it looks fine to me. probably built better then anything you could buy off the shelf. but as someone who repairs lights daily ive seen what happens when they fail. now anything can fail at anytime as hoppy implied in his post and i know that. if your diy stand collapses youll have a big mess. if your diy co2 fails youll have dead fish or an algae bloom. but if your diy light fails your f'ed. good luck.
your co2 tank can fall on your toe and brake it or your valve can brake off and it will rocket out the window.

if you know enough about electrics, the power conversion to LED current would be the effect of throwing batteries in your tank. even the fish would survive.
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Old 05-19-2011, 09:54 PM   #386
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I know that Cree XR and XP series diodes are far and away the most popular emitters in the hobby, but I feel they have less than ideal spectral distribution. For my project, I decided to use LedEngin LZ1 neutral white for my main source. Unfortunately, even those have a big shortfall in CRI compared to the flourescent sources I am replacing. To supplement the white LEDs and hopefully correct the CRI up to something more acceptable, I added Lexeon Rebel 505nm (cyan). A careful comparison to natural daylight also shows a slight defficiency in the far red end of the spectrum so I also added LedEngin reds in both 660nm and 735nm. The 735 is sketchy, but I wanted to try it. The 660s are at a photosynthetic response spike and also help show off the red in my fish.

You may wonder about the ultraviolet end of the spectrum...After testing with three or four different colors from 400nm down to about 320nm, I found the fish turned black (no flourescence), floating particulates in the water flouresced unaesthetically (turning the water milky in appearance), and read several articles indicating that UV was at best marginally beneficial (if not detrimental) to the health of both the fish and the plants...so I elected to leave that piece of the spectrum out. (not to mention the emitters are expensive)
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Old 10-24-2011, 02:17 AM   #387
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can someone tell me about how 660nm led's work in fresh water fish tanks?

Are they good but make things look funny? or they asking for an algae bloom on biblical levels?

Wondering if 660nm LED's should be considered as cree makes them in 3W sizes too.
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Old 11-28-2011, 10:42 PM   #388
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I have no direct experience with the 660nm lights, but maybe I can point you at some info.

I've been reading some studies on the effects of light frequencies on aquatic plant growth and come across some interesting results.
Sadly I haven't saved my sources, but google is your friend too!

All studies I looked at were done with freshwater aquatic plants typically found in an aquarium. I think that is quite important!

One study I looked at concluded that red light was implicated in creating compact branched growth, green light(as might be found in a deeper lake) gave leggy growth(long internodes, lower chlorophyll) with white light and blue light giving a more 'normal' growth.

The upshot for me, is that my next LED purchase will be a combination of warm white, that has a good dollop of the 600-700nm wavelengths, whilst not being exactly short of blue light either, and the midrange white LEDs so I don't end up with a 'yellow' tank. These should compliment my cold 'daylight' whites and provide well for the plants.
Time will tell.

If I had gone the 'many small sources' route, I would consider mixing in some reds to encourage the compact growth, but I've seen some messy shadows from that sort of set-up so I'd be thinking hard about the design. I didn't, I've gone for few lights, but powerful.
My feeling is that the white LEDs now available have a suitable enough spectrum coverage for a good looking, strongly lit, healthily growing planted aquarium.

The main focus of my reading was how plants adapt to different wavelengths as they become available, for example as water depth changes or the plant grows.
It seems that some plants do adapt to different light frequencies and some don't...
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Old 11-29-2011, 06:16 AM   #389
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Quick question for you folks running LEDs.. How much far do LEDs with optics stick out from the surface they're mounted to? I'm trying to figure out how much clearance I need for the enclosure.
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Old 11-29-2011, 01:28 PM   #390
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I just can't resist, no offence meant!

http://lmgtfy.com/?q=led+60%C2%BA+optics+data+sheet

The answer is there.
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