diy LED questions - The Planted Tank Forum
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post #1 of 3 (permalink) Old 06-29-2013, 12:37 AM Thread Starter
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diy LED questions

I am trying to understand LEDs and I think I've almost got it, but I got a couple questions. My first question is about wattage, if i push more wattage that will make a bulb brighter? (Obviously need to stay in the bulb's limits) reason I ask... I just recieved my roll of 3528 SMD LED strip todays. There is 300 LEDs split into cuttable moduales of 3. Each LED is said to produce 7~10lm and consumes ~.08w. This would mean each roll consumes 24w and produces 2100~3000lm. I used a power supply I had just see if this would be enough for my current tank build before I ordered a powersupply and probably another roll. The power supply I have is 600mA at 12vdc. I plugged in a strip of 48 leds which needs 3.84w. If I did my math correctly then 600mA actually is .6w, so with a higher wattage plug these shoild be brighter right?
Also, back to lumens, i assume that these numbers are at 0 feet, so would it better if I use a larger LED which will probably penatrate deeper with more lumens? These 3528 SMD are used commonly for under cabinet lighting and the pics look like they are equivalent to flourescents. I know in low tech planted tanks we don't want a lot of light, but now I think I went too
If these won't work then I was looking at 1w Epistars. I have a 3w epistar fixture now over a plant and it is doing really well, but the fixture is dimmed to 1/4 of it's power, so am I right to assume I can use the 1w if not the 3528's? Thanks guys for your patience
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post #2 of 3 (permalink) Old 07-01-2013, 03:29 PM
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You've asked a bunch of questions about driving the LEDs. It's important to understand how LEDs operate in order to answer your questions.

Basically, high power LEDs are (typically) driven by constant current drivers. You choose an LED, and then you determine what current you want to run it at, based on it's specifications. Then, you go choose a constant current power supply (LED driver) that can supply the current you want, and can push enough voltage to drive the number of LEDs you want in a single string. Wattage is usually a secondary concern.

The thing that causes most people to struggle with this is that for almost everything else we deal with in terms of electronics, the assumption is that voltage is the important variable. With LEDs, current is the important variable. Because so many consumer electronics are designed to operate on a constant voltage, most of our power supplies (like the one you probably experimented with) are constant voltage.

Typically, you would not drive HP LEDs on a constant voltage power supply, because it makes it hard to know for sure what's happening to the LEDs.

Books could be written about this, you might be best off doing some reading on the web about HP LED basics and then asking any questions you have.

You also asked some questions about lumens. Lumens are a measure of the total light produced by a luminary. There's no spatial component - i.e. distance or coverage area. Every photon that comes off the LED is included in that 7-10lm number. You mention "at 0 feet" or penetrating deeper - those two statements both imply a spatial relationship. In this hobby, we often measure light in terms of PAR. PAR assumes a given spatial relationship (i.e. "PAR at the bottom of the aquarium directly under the light" or something like that). You can't convert between PAR and lm without knowing the spatial distribution of the light source. This is why, for LEDs, it's important to know things like how the light is distributed (most raw LEDs are spec'd with a "viewing angle" that tells the entire width of the light). This is where optics come in to play - a tighter optic means a narrower distribution, and hence for a given lm, higher PAR over a narrower area.
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post #3 of 3 (permalink) Old 07-01-2013, 04:50 PM
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I tried using two reels of those LEDs to light a 10 gallon tank. I would recomend either using high power LEDs with a constant current driver, or stick with traditional lighting.
To get sufficient light with those strips you need to come close to filling the entire area above your tank with them. They are ineficient because they use resistors to limit power through them instead of using a current driver. Also they have terrible longevity. After about a year and 3 months of less than 50% duty the light output is about half of when I first made the panel
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