Blue LED light purpose...

[Phoenixtx01]

Here is a question for the pros...

what is the purpose of the blue only light on my led lights for my tanks?  They all have them but not sure when or why to use them... planted 90 gallon community tank with 4 black mollies, 20 black neon tetras, 2 black angels, 10 peppered cory’s, 2 black spotted bristlenose plecos + fry... 

should I ever use the blue light or no? 

[Fish Folk]

I think it's basically up to your aesthetic preference. Subtle blue LED points may make water, substrate, and surfaces appear "cleaner" and more "crystalline." Yellow & Red light points are "warmer." From plants point of view, I do not think that they really benefit one way or another from colored LEDs. There's more involved metrics there regarding Kelvin, Spectrum, PAR, etc. If your blue LEDs are in blocks or pods on your light, then they'll cast a really blue "sheen" through the water which can be interesting . . . but again, it's up to what you prefer.

[Yanni]

I think blue lights are just for glo fish or just because it looks good for some people. If you ever need extra algae for your bristlenose just flip the blue light on.

[Phoenixtx01]

Yeah I see that, I wonder if it’s better on the fish as I have the light on a timer at 3pm to 11pm but maybe at 9pm switch to blue 

[CT_]

I always thought it was weird to have a blue "night" mode.  Blue penetrates water the best so I always assumed fish could see it the best too. 

One thing I don't see very often (ever?) is advertising red vs far red lights.  Controlling the ratio can control whether plants think they're shaded and therefore if they grow straight up or outwards more. 

[Hobbit]

I thought the blue setting had something to do with growing coral. But I know nothing about saltwater tanks so I could be totally wrong.

[Tanked]

My blue light only function was marketed as "moonlight".  It is interesting to a point, but seemed to project individual beams of light that highlighted the smallest particulates not seen in daylight.

[gardenman]

The blue moonlights are mostly there so the tank isn't a black hole at night. If you leave them on during the day they won't hurt anything and could help your plants grow. Dedicated plant lights are very strong in the red and blue spectrums and create a purple glow. Those are the two segments of the light spectrum that plants respond strongest to. They're really a pain to look at though. 

I don't use the moonlights as I have a little Wyze cam pointed at my tanks and the fish behave the same with the lights off as they do with the lights on. The Wyze came lets me see the tanks in complete darkness and the fish behave just like they do during the day. Except for one bristlenose pleco in one tank. When the light goes off, he starts to get far more active and then swims upside down under the floating plants. He grabs them with his mouth and pulls them under the water looking to see if any food was on top of them. It's really funny to watch. I've gotten to the point where I'll put some food atop the floating plants before the lights go off just to reward him and I'll sit in the darkness and watch him on my phone. He's a clever little guy. He just grabs a floater, pulls it down a couple of inches and gives it a shake then lets it go and grabs another one. If any food comes off he follows it to the bottom, scarfs it down and then goes back on the hunt. I never knew he did that until I got the camera. He doesn't do it when the light's on, but when the light goes off, he comes out to hunt for food and knows there's food atop the floaters. 

[L.W. Wetarm]

All I know is my hair algae problems went away when I cut my “moonlight” time down to half an hour in the morning and half hour at night. 

[Daniel]

Light at the higher frequency wavelengths (blue light) is important for photosynthesis in plants:

The downside is algae is a plant. 🙂

Most growlights have a fair amount of their light output down in the blue part of the spectrum as a way of encouraging plant growth. The part of the spectrum plants don't need so much is the middle part which is why plants appear green to our eyes. Also we have a preference for the middle part of the spectrum where blue and red and green all contribute and which we perceive as 'white'.

[Casual aquatics]

So did we decide colors do or don’t grow plants better 🤦🏼🤷‍♂️🤔🤔🤔👆👆👆👆👆👆👆

[Daniel]

6 hours ago, Casual aquatics said:

So did we decide colors do or don’t grow plants better

Blue and red grow plants (photosynthesis) better than anything else, and grow algae better than anything else. But blue plus red plus green equals white light which most people find very pleasing to look at and also grows plants.

[gardenman]

Commercial grow lights tend to give off a purple light due to the red and blue spectrums being highlighted. I grow my own seedlings for my garden and have used 6500 K "sunlight" bulbs prior to this year.  This year I added another tier of lights to the plant stand and bought four of the 4' long LED grow lights in the blue/red spectrum to try out. I have a small bowl of floating plants I put under the new lights to test them out and the lights were too close initially and burned up the frogbit and red root floaters. The salvinia and duckweed did fine though. The lights have now been moved a bit higher. I've now got three flats of geranium seedlings hogging most of the new plant lights but once the plants move outside for the spring and summer I'll play with those lights some more with aquarium plants. I would not use them in an aquarium you want to look at as they're quite unpleasant to look at, but for plant production, they might be pretty good. Floating aquarium plants cost an absurd amount considering how quickly and easily they multiply. The same with many of the mosses. I plan to try seeing what the production rates would be under those lights and maybe start selling some of the plants online.