Old plant grower, LCD lights, needs heip! - Lighting - Aquatic Plant Central

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Lighting Science of Aquatic Lighting - Aquarium lighting is essential for healthy aquatic plants. Discuss proper aquatic lighting for your plants and fish here.

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Old 01-15-2020, 04:37 PM   #1 (permalink)
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Default Old plant grower, LCD lights, needs heip!

I've been growing aquatic plants with some success for more than 20 years. My tanks have been low tech and soil-based, with no added nutrients except fish waste. And light. And that's the source of my question.

I'd been using about 2 watts per gallon of T12 and T8 fluorescent tubes, usually in shop light fixtures. Everything was rosy. Then the tubes and the fixtures started to die, and replacements were hard to find, then impossible. I bit the bullet and decided to buy a LCD fixture for my 29. I got a recommendation and bought one about 3 years ago. The price was quite high but the light was amazing. The plants did great!

But the price was too high to justify buying LCD's for my smaller tanks. I made do with various combos of screw-in LCD bulbs and desktop fixtures, but this was barely acceptable. Then I recently found some LCD fixtures in a Pets-whatever at very reasonable prices.

So after all these words, here are my questions:

1. With tubes, I knew that 2 WPG would work. How is LCD lighting measured? By the number of LCD's in the fixture? By lumens? PAR. if it's available (but there are so many variable . . )?

2. With the tubes I would chose a Kelvin of 5000 - 6500 with a CRI in the mid-90's. What
metrics are used in the LCD world?

3. It could be my eyes, but it seems to me that the LCD's don't illuminate the sides of fish as well as the older bulbs. Do the tubes produce a more diffused light? Are the LCD's more point-to-point, like lasers?

Thanks for your help and your patience. <g>

Bill
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Old 01-15-2020, 07:36 PM   #2 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

LEDs (light emitting diodes) are point sources of light. Each of them alone is a pretty weak light "bulb", but most LED aquarium lights use dozens of them spread out over a large area. Unlike fluorescent lights they don't need reflectors, and each tiny LED produces a cone of light about 120+ degree cone of light. So, they cover a lot of area with light coming from all directions. Many manufacturers of these light fixtures also measure the light intensity from them at various distances, expressed in PAR dimensions, photons per square meter per second. Look for the intensity at the distance your light will be from the substrate. If that is 20-40 it is low light, 40-50 or 60 is medium light, and above 60 is high light.
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Old 01-15-2020, 08:02 PM   #3 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

LCD colors are measured in kelvin as well. I think naturally they’re 5500k. For different colors, the lens is coated with a certain color.
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Old 01-16-2020, 06:10 AM   #4 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

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LCD colors are measured in kelvin as well. I think naturally they’re 5500k. For different colors, the lens is coated with a certain color.
Color temperature doesn't really apply to LEDs since they produce much of their light in very high peaks at specific wavelengths. Different phosphors are added to the LEDs to adjust their light spectrum so it is more useful, and that can make them provide mostly red, blue, etc. colors. That lets the manufacturer rate their LED lights by color temperatures comparable to fluorescent lights. Good LED lights have some very red diodes, some very blue diodes, and a good mix of other colors, so the light they generate contains most of the wavelengths of light needed by plants, plus a pleasing appearance for human eyes.
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Old 01-16-2020, 04:01 PM   #5 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

Thanks for your responses!

Please pardon my obtuseness.

Are we saying that all Kelvins in the 400 - 700 nm range produce about the same PAR values, all other things being equal?

Would the answer be the same for both LED and tube-generated light? Why?

Since par diminishes with the distance from the light source, what would be the difference between a a fixture designed for a deep tank and a shallower one, given the same footprint? More LED's? More voltage?

Thanks again,

Bill
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Old 01-17-2020, 08:08 AM   #6 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

Are you sure the various colors are from the coating? I read that some colors of diodes are kind of recent and have different chemicals. I could and might be totally wrong
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Old 01-17-2020, 08:34 AM   #7 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

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Originally Posted by aquabillpers View Post
Thanks for your responses!

Please pardon my obtuseness.

Are we saying that all Kelvins in the 400 - 700 nm range produce about the same PAR values, all other things being equal?

Would the answer be the same for both LED and tube-generated light? Why?

Since par diminishes with the distance from the light source, what would be the difference between a a fixture designed for a deep tank and a shallower one, given the same footprint? More LED's? More voltage?

Thanks again,

Bill
"Kelvin" is the absolute temperature in the Celcius temperature scale - what used to be Centigrade degrees. It is the name of the absolute temperature scale. A Celcius degree is the same as a Kelvin degree and is a measure of temperature. The wave length of light is often measured in nanometers or "nm". 400 to 700 nm wave length is the range of wave lengths, or colors, of light that plants can use for photosynthesis. When light sources are given a Kelvin temperature it means that a black body at that temperature would radiate light with about the same intensity vs wave length as the light source produces.

Light fixtures are not designed for any specific shape of aquarium, other than that their length is always intended to be equal or less than the aquarium length. If a light is suspended high above the aquarium the light intensity will vary much less over the full height of the aquarium than for light fixtures sitting right on the top of the tank. But, with most LED lights, the large angle cones of light from each individual LED will cause a lot of spill over light with the light high above the tank.
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Old 01-17-2020, 11:32 AM   #8 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

I was using "Kelvin" in the context of growing plants, where the term is essentially synonymous with "color temperature". In the past, a Kelvin of 5000 to 6500 degrees was considered best for most aquatic plants. The sun at the equator approximates that. Are we saying that doesn't matter with LED's?

To restate my question about light and tank depth, how does one determine how many LED's a tank a tank needs?

It would seen that a deep tank would need more light that a shallower one. Some fixtures contain more LED's than others with the same dimensions and they'd then seem to produce more light at the bottom of the tank, but do they?

Thanks again!

Bill
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Old 01-17-2020, 01:45 PM   #9 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

Quote:
Originally Posted by aquabillpers View Post
I was using "Kelvin" in the context of growing plants, where the term is essentially synonymous with "color temperature". In the past, a Kelvin of 5000 to 6500 degrees was considered best for most aquatic plants. The sun at the equator approximates that. Are we saying that doesn't matter with LED's?

To restate my question about light and tank depth, how does one determine how many LED's a tank a tank needs?

It would seen that a deep tank would need more light that a shallower one. Some fixtures contain more LED's than others with the same dimensions and they'd then seem to produce more light at the bottom of the tank, but do they?

Thanks again!

Bill
Fluorescent bulbs have long been categorized as "daylight", "warm", "cool", etc. and more recently by a color temperature, one of which is 6000-6500K. But, even those bulbs didn't really come close to matching a black body at that temperature, because fluorescent bulbs have several high peaks in their spectrum, instead of a continuous, smooth spectrum. Plants don't need any specific color temperature bulb. They do need significant light in several parts of the light spectrum, whatever type of light source it is.

There is no specific equation that I'm aware of for determining how many of what type LEDs are needed for various sizes of tanks. When I was building my own LED lights I measured the light output of single LEDs, and, for tape mounted LEDs, the light output for various rows of tapes of specific types. And, I was able to use that to get a pretty accurate guess about what any group of LEDs would produce.
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Old 01-17-2020, 02:10 PM   #10 (permalink)
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Default Re: Old plant grower, LCD lights, needs heip!

Get something really strong but make sure you have a good dimmer, etc and turn it down to whatever turns out to be appropriate.
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