Inquiry on LED dimming

I'm building a custom fish tank for a client who requested the lights dim to mimic the sunset on his timer.
I was told LED's change color with voltage, is this true and what components would I use to automate this 15-minute sunset? Or, is there an easier/safer method?

I'm fairly educated in electronics, and can read schematics & build simple circuits (i.e. photocell switch). The client's light requirements are
80: 5mm 25mA 3.4v diodes, and
20: 5mm 20mA 3.2v UV diodes,
via 12v 1000mA DC.

Any advice or links are greatly appreciated.

Leds have some color shift but it varies with the tint of the LED and is related to the lottery. If you want to mimic sunset you will probably have white LEDs and red or orange LEDs that fake the color shift. my advice is FORGET the 5mm LEDs entirely as the longevity of all but perhaps the nichias is short, invest in high power LEDs at least luxeon 1 if not rebels or crees. UV LEDs have a really really short life compared to standard LEDS from what I have heard.

Ideally I use hi-po arrays, but in this application the 5mm are necessary for the lighting effects on the plants & coral. Clients haven't complained of any burn-outs in the last 5 years, but replacing a few clusters with some 1W diodes would be a smart idea.
The UV's definitely don't last as long, but it's still superior to the old UV lamps (no ballast flicker = healthier fish... important when they cost $300 ea.)

I'll also take your advice on the sunset, seems more reliable anyway.
Thanks a lot!

I still don't see a justification for why you're using 5mm LEDs, or what 5mm LEDs do that power LEDs (1-3 watt) won't.

On my 10gal saltwater nano tank even my mushrooms require a minimum +1000 lumens, so your client isn't going to grow anything other than algae with 80 5mm LEDs.
Unless this is a moonlight or something, but even then I don't see why you just don't use royal blue Crees.

FYI - UV LEDs don't do a thing for photosynthesis. They color up corals, but then again so do royal blue Crees.

See this thread over at the nano-reef forums for reef lights built with LEDs. Might have some ideas for your project in there.

Well first, I already have a ton of flat-top 5mm's, and it's nice to have the ability to start small & work up to achieve the effect I want. I'm starting with 80, it may increase, which could call for an upgrade.

Second, it depends on the distance the light is from the organism. Each of the diodes emits ~12 lumens, and they're all within 5 inches of the plants. The CO2 injection also reduces light necessity (and regulates pH), plus coral really only needs high exposure to procreate.

Although equally used for the effect, the light emitted from the UV's is at 400nm, which is appropriate for photosynthesis; it could be debated, but it's worked for my other projects.

It takes a while for the plants to merge, so I'll keep your advice in mind during the nursing phase in case the light levels are indeed too marginal. But finite efficiency helps minimize upkeep & cost for clients, which keeps me in business.

dunno on the UV-led,
but when You can safe the effort of placing 80!!! 5 mm white ones by just using 3 high power led ... ist there really a question?

Even when You use - say - 10, underdriven but with more options on lighting architecture, that were much time effective
(+ the bonus of simply raising power, when needed somewhen in the future)

I do see that You want to use already available parts - I also do that - but this much more work?
I would quit here

LEDs do change color when under/over powered. However, the change of color is not predictable and the efficiency of the light output will be off. This is not the recommended way to change color.

The correct approach is to modulate the power to the driver so the LEDs are on/off 100% over time. The gives you the effect of dimming. And you effectively get the color change you want when you have 2 or more colors which dimmed against each other.

The most popular colors for fish tanks are Cool White and Blue (sometimes Royal Blue).

Here are some photos of a fish tank project that I'm working on right now.

You may find these interesting. The Blue below doesn't photograph too well. It's Royal Blue.

3/4s of the LEDs are Luxeon Rebel Cool White and 1/4 are Luxeon Rebel Royal Blue. The entire system consumes about 350 Watts of power (26 Amps at 12 volts).

The Royal Blue used as a single color is over-kill for moon light, but in combination with the white serves to add more blue for daylight color adjustments.

I know nonsoundFLUX is building something according to the specs from his client, but just to clarify some science here:

- How are you getting 12 lumens from a single 5mm LED?

- UV-A radiation has been shown to have more negative effect on plants than positive, and the spectrum involved with optimum photosynthesis is pretty much hard science. The reason many plants, such as corals, color up under UV-A is because they are protecting themselves from the radiation.

- CO2 injection is something done only with freshwater tanks to stimulate plant growth. You do not inject saltwater tanks with C02 unless you want to kill everything with a Ph crash.

- The lighting requirements for saltwater corals are about 10x over freshwater plants. In fact, the shoplight in the ceiling is often enough to provide enough PAR for shallow freshwater plants, so perhaps that is the case here.

SuperbrightLeds.com carries a 1watt ProLight UV LED.

Blasterman, you should know better than saying corals are plants. Also, CO2 can be used in reef aquaria, but typically only in calcium reactors.

Some clarification needs to come from the OP as to whether this is a planted freshwater or a reef tank. If this is reef, no amount of 5mm LEDs will be adequate. They barely put out enough light for low light corals to survive, let alone grow. I think it is unfair of you to deliberately limit the amount of light in the tank to only have any coral survive. It's not healthy.

nonsoundFlux said:

I'm building a custom fish tank for a client who requested the lights dim to mimic the sunset on his timer.
I was told LED's change color with voltage, is this true and what components would I use to automate this 15-minute sunset? Or, is there an easier/safer method?

I'm fairly educated in electronics, and can read schematics & build simple circuits (i.e. photocell switch). The client's light requirements are
80: 5mm 25mA 3.4v diodes, and
20: 5mm 20mA 3.2v UV diodes,
via 12v 1000mA DC.

Any advice or links are greatly appreciated.

Click to expand...

I think LED's have different shades on them changing their colors.