light wavelength and lumens

[cavycat]

Hi,
I have a 400 lumens Megaman Plant bulb, which has concentrated blue and red light.
I also have a general full spectrum bulb that emits 1800 lumens and has a color rendering index of 95. It's supposed to be as close to sunlight as you can get.

Which of the two is better for my orchids?

Thanks,

Sara

[cb977]

Hi Sara,

I don't have an answer for you but I'm going to move this thread into the Growing Under Lights forum...I think you'll have a better chance of getting an answer there

[Magnus A]

I would say that the full spectra 1800 lumen bulb is WAY better! The plants CAN use more than the red and blue parts of the light and you get 4.5 times more punch. Then you get a nice neutral light as a bonus! I would not hesitate 1 second to use the 1800 lumen bulb!

[JPB]

I would say that it is hard to compare.

First, lumen is based on the human eye which has a much stronger perception in the green than in the red and blue.

Second, plants do mainly absorb radiation in the blue and red wavelengths and no/less in the green/yellow bands.

So comparing lumens from these lamps is not useful IMO.

[Magnus A]

If you look at the spectral distribution, which wave lenght is emitted, the color temperature is OFTEN not always defined by one extra strong band not all wave length.
It is correct that the lumen is defined as the light at a certain wavelenght (green light = 555 nm) but in reality the number reflect the total amount light emitted over all wavelengts.

I still stand that a good colored light (high CRI) high output (high lumen) is ALWAYS better that low CRI and much lower output. Your orchid will defenetly look better under the stronger lamp and you will get more usefull light from it!

[JPB]

I think we agree, but from different views. Artificial lights are not sufficient at al to generate the PFRs (Photon Flux Rates or irradiances) the plant sees in the field (up to 1000 uE.m-2.s-1 even on a cloudy day). The more light, the better. Preferably diffuse light.

Apart from the "naturalness"/high CRI of full spectrum lamps (more natural colour of plants, and a cure for depressed horticulturist :-), it is the best way to go. I have some Megaman plantlamps (mainly red and blue) and i still have to see if they work properly..

I did some homework and found/recalled the following:

The absorption spectrum of all plants for the main photon-capturing pigments is the blue and red.

However, the quantum yield of photosynthesis as measured for each wavelength (400-700nm) shows a different pattern: A dip in the blue and a good yield in the green region. But these are measured under monochromatic lights.

To make it even more complex:
Under certain monochromatic conditions (blue and red), photsystem II cannot perform properly under the given wavelength only. Addition of green light solves the problem and PSII can work properly again.
So there is a (photosynthetic) benefit to have green light in the setup, although you would not conclude that from the chorophyll absorption spectrum (as I did in my prvious post).

Just a little science....still learning...

[Magnus A]

JPB, I agree with you!

The litterature on what has been investigated on green plants and the core of photosynthesis is HUGE! There is contradictions and very few species investigated!

/Magnus