DIY LED Coverage

[Fishsticks]

I'm designing an LED light for a 30 l cube and am having trouble deciding how high to position the lights.

Even though it's a small tank, I've chosen to use optics for reasons that probably belong in the DIY forum rather than here. But the effect of that is that I'll potentially end up with areas at the top of the tank that fall outside the beams and will be lit by only reflected light.
In designing the light I've aimed to have full coverage of the tank about half through its depth, which means that the greater portion of the surface won't be directly within the main 'beam' from the lights. The periphery of the tank in the upper half will therefore also not be directly lit. I'm planning to position the LEDs very close to the top of the tank - perhaps just 15-20 cm off the surface so in fact just about 1/4 of the surface will be within the beam cast by the optics.

I'm not quite sure how this will work in practice - is there any conventional wisdom as to how the field of light should hit the tank? Do people normally aim to 'just' cover the entire surface, 'just' cover the entire substrate or (like me) somewhere in between?

Significantly raising the lights and using narrower optics would of course help, but I'd like to avoid doing that because of where the tank will be situated.

 

[wazuck]

I would actually like to hear about your choices in optics and which LEDs you are using. Also is the system dimmable? My main concern is that your going to throw too much light into the tank. I normally try to go for an even coverage with the light spread.

 

[Fishsticks]

I initially put a lot of thought into choosing LEDs, optics, etc. but was frustrated by the amount of information available - a lot of detail but not enough to draw any decent conclusions when it comes to designing a light.

I went with white Cree XP-G LEDs. The ones I picked weren't labelled cool/warm/etc. I had initially planned to use a combination of cool white LEDs (for plants) and warm white (for me) on individually dimmable channels, but when I looked into the XP-G I found that the colour temperature already seemed to offer a reasonable compromise.

In terms of numbers, I started off trying to find PAR data, then decided that for a small tank the LED cost isn't that high and I would just take a guess, add an extra LED or two, and then dim the LEDs down to what I want. Looking at other people's builds, I decided that 9 XP-Gs (which are 5W and very efficient) would provide me with too much light and could be run under-power (and therefore cooler). I can decide how much to under-power the LEDs once I've build the light and am in a position to experiment with it.

I'm going to use a single 48W dimmable power supply (from Meanwell).

In terms of optics, I'm just using bog-standard plastic lenses. The choice of angle is very much tied into how high above the tank the LEDs will be and how wide I want the coverage to be. The choices I'm considering are 60, 45, or 40 degrees - anything broader will spill right over the top of such a small tank unless the LED is just a couple of cm off the surface, and anything narrower will need to be mounted much higher than I'm planning.

When you say an even coverage, are you talking about an even coverage at all depths, or just e.g. at the substrate?

 

[wazuck]

First off that is a lot of light for a 30cm cube. I would personally run just 4x3w LEDs. Even that at full power they would be more than enough light. I would, like you say use different colours of LEDs to get a better colour pop in the tank as using one colour temp tends to give a washed out look. Optics really aren't needed at those depths. And will only make the light more concentrated. So again consider maybe 4x3w with optics if you really must have that directed beam. The other thing with optics is that the tend to make different colours of LEDs blend less effectively. Soo you may end up with different colours within the tank. Anything else you need to know then just ask.

 

[Fishsticks]

Thanks for your comments!

I was actually planning on using just the one colour LED, but I wonder now if I should review that decision. I'm tempted to throw in a blue LED at least, just in case I find the whites too warm. Although I've not seen anyone do it (and appreciate that it would be of no benefit to the plants) I had wondered about adding a green light also - would it enhance the appearance of the plants in my tank or is it a silly idea?

I hadn't intended to run the 5W LEDs at full throttle - I chose them mainly because they're very efficient, and had planned to run them significantly dimmed - perhaps at just 1/3 to 1/2 of their max current. A lot of my reading has been on reef forums (where they love their LEDs!), but I reckoned that using about 6 LEDs should be quite adequate, but decided to up that to 9 on the basis that the cost of a couple of extra LEDs was minimal and that a larger number of dimmer light sources might provide me with a more uniform light. That might be misguided however.

I'm right at the beginning of my build (all I've done is order some LEDs and a driver) so am wide open to suggestions.

 

[Fishsticks]

Oh, and the reason I'm looking at optics at all is simply that the XP-G has a very wide viewing angle at 125 degrees. The tank will most likely sit in my living room and I don't want the light to be dazzling when viewed from the size. I would happily do without if there was a simpler way to avoid spilling light to the side before it hits the tank.

I considered adding a deep lip around the edge of the light to avoid the spill, but unless the light is practically on top of the cover glass then that lip would need to be quite deep.

 

[rolexbene]

A nice little tip for small led's setups, is to buy a small amount of RGB led strip with remote control. You need to conceal this in your lighting unit, I did the same with a standard overhead 40w CFL light. You can then change the colour temperature of your cool-white leds with the auxiliary RGB's. It's great for messing around with different temperatures of lighting to find the right ballance and can be used as a temp or permanent solution. Also if the tank is up against the wall it can make a nice sunset scene, by placing these behind the tank instead of in the light.

44 Keys IR Remote Control Controller for RGB 5050 LED Light Strip 12V #2 | eBay
1M/2M/3M/5M RGB LED Light Strip/24 Key/44 Key IR Remote Controller/4-pin Cable | eBay

 

[Fishsticks]

Thanks - that is a nice tip. I'd thought about it for the backlighting and was going to experiment once everything else is up and running but it hadn't occurred to me to build RGB LEDs into the overhead light.