T8-LED info

[naoki]

I put some information about a highly efficient T8 LED on my (brand-new) blog. I thought that it may be interesting to some of you.

Orchid Borealis: Prime time for T8 LED lighting?

[estación seca]

Thank you for the information, which represents a lot of work on your part.

Many people use 6500K CFLs for growing, rather than 3000K or 4000K, since 6500K are supposed to have better PPFD than lower color temperatures. Did you investigate higher color temperature LEDs, or do the data from the manufacturer show they are not superior to the lower color temperature LEDs in terms of PPFD?

[naoki]

Estacion, I have some data from T5HO, but I think PPFD isn't so different between the color temp.

4' 54W T5HO
3000K (about 2 months old): 82 micro mol/m^2/s
4100K (brand new): 83
5000K (brand new): 85
5000K (about 2 months old): 80

2' 24W T5HO
6400K (brand new): 58
6400K (2 years old): 33
Odyssea Plant (Purplish, new): 81
Odyssea Platn (3 months old): 62

I don't have 6500K 4', so I can't compare directly, but I think the difference in PPFD is is pretty minor.

People who is claiming higher PPFD is probably confusing PPFD with foot-candles? The 4' 54W data shows small difference in PPFD, but in terms of foot-candles, there are larger differences.

Now, the emission spectra of white LEDs are quite different from those from fluorescent lights. Most of the white LEDs are blue LEDs + phosphor coating. So there are two peaks (blue and another which has longer wave lengths). Once you start to go beyond 5000K, the blue peak dominates (basically, you can think that it has thinner phosphor coating). So the total photon output of higher K LED could be higher, but for photosynthesis, blue is a bit less efficient. If you look at the curve, anything above 5000K seems quite a bit unbalanced for plants (no evidence here), so I haven't used anything beyond 5000K.

I have measured PPFD of 5000K and 3000K Cree CXA3070, and they were almost identical. This means 3000K, which contains more red, is more efficient for plants. Note that PPFD doesn't put more weight for red light. So in theory 2 photons of blue gives the same PPFD as 2 photons of red. So for a given amount of PPFD, light with more red is better for photosynthesis (this is called yield photon flux).

But we are talking about a pretty small difference, so higher K LEDs probably would be ok, too.

However, in addition to photosynthesis, color influences other aspects of plant growth.
http://cpl.usu.edu/files/publication...b__2576523.pdf
I haven't seen much info about how it influences the orchid morphology, though.

[estación seca]

Originally Posted by naoki

Now, the emission spectra of white LEDs are quite different from those from fluorescent lights. Most of the white LEDs are blue LEDs + phosphor coating. So there are two peaks (blue and another which has longer wave lengths). Once you start to go beyond 5000K, the blue peak dominates (basically, you can think that it has thinner phosphor coating). So the total photon output of higher K LED could be higher, but for photosynthesis, blue is a bit less efficient. If you look at the curve, anything above 5000K seems quite a bit unbalanced for plants (no evidence here), so I haven't used anything beyond 5000K.

The whole post is very useful; thank you. The difference in emission spectra between LED and fluorescent of similar K ratings is something I didn't know.

I haven't looked at information on the various fluorescents for about a year, but I recall many people growing underwater plants were quite certain the 6500K fluorescents were much superior to lower K ratings. It may be because water attenuates lower-energy red photons much more than higher-energy blue photons, so a bulb producing more blue than red photons will provide better flux to the submerged plant. However, I also know indoor hydroponic herb growers (of which I have never been one) strongly prefer higher-wattage 6500K compact fluorescent bulbs over lower K rated bulbs.

[naoki]

Very interesting about the aquatic plant. The energy argument makes sense. Do you do planted aquarium, too?

I think some 100% aquatic plants have a slightly different photosynthetic action spectrum (I forgot the detail, though). But many plants which we grow in aquarium are facultatively aquatic. Also, with stem plants, I wonder higher K gives more compact growth form.

[estación seca]

We're far off topic for orchids, so if we continue this discussion, maybe it should go to another forum, like "Off Topic - Totally" at the bottom of the Forums page.

I have an outdoor pond and indoor aquaria. I grow true aquatics, none of the things that can survive submersed for a while.

In a sunny outdoor pond plants grow magnificently with little care.

Growing underwater plants under lights is frustrating. There are not many data available for light availability at different depths of water from different kinds of fixtures, so hobbyists tend to use the hit-and-miss prinicple. Aquarium fluorescent light fixtures usually have plenty of data available on output, but not on penetrance. Many aquarium LED fixtures tend to have little to no data of any kind available. I suspect manufacturers assume buyers are interested in looking at fish rather than growing plants, and may substitute whatever LED elements are most cheaply available at time of manufacture.

An aquarium setup with prolific plant growth, after a complete takedown, cleaning and rebuilding, planted with the same species of plants and under the same conditions, may not grow at all.

Most advanced underwater gardeners bubble carbon dioxide gas into their aquaria to improve plant growth. You don't see this on the YouTube videos of unbelievable underwater landscapes, but it's almost always there.

I haven't wanted to go to this much trouble. The plants grow well in nature without this, and I'd like to figure out how to grow them without another complicated apparatus.

Then there is the problem of aquarium fish that eat plants. My experience is fish that aren't supposed to eat plants, do eat plants at my house.

[bethmarie]

Thanks for this and your blog post. Very informative, detailed and helpful!

[naoki]

Thank you, Beth.

Estacion, that's cool you do aquatic plants, too. Well, plants are plants, and most plants need light, so it isn't quite off-topic! I started planted aquarium about 30 years ago after seeing Mr. Amano's work in photos. I've been doing it on and off, but I'm not quite up-to-date with the current state. Since I can't get cool plants and fish from local fish store (and time is limited), I have only low-key 40g with bunch of Cryptocoryne, Anubias, and a couple Echinodorus. I think all of these are considered true aquatics, but they spend some of the time above water, right? Frequently, they modify the leaf forms when you grow them above water (and usually grow faster above water). This is what I meant by "facultatively aquatic", but maybe it is not the right word. There are some species like Ceratophyllum (hornwort), Potamogeton (pond weed) or Elodea which don't have above-water form (and die). But even stem plants like Ludwigia, Hygrophylla, Bacopa etc grow better above water (basically CO2 limitation which you mentioned), and they die above water. I've done CO2 injection, but the plants grow too fast, and it became tedious to keep up with.

There is a South Africa based group of people who has been doing great work in analyzing different source of light for aquatic plants. I learned quite a lot from their works. TyroneGenade, who hangs out in SlipperTalk, is one of them. He can send you a nice excel spreadsheet, where they calculated PAR of many different fluorescent bulbs and LED lights from emission spectra data provided by the manufacturer.