Watts of LED per square area needed for growing orchids?
 

TLDR: how many watts of LED per square area is needed for growing low to moderate light loving orchids?

I have an orchid growing area of 213cm length x 47cm width by 126cm high for low light growing species such as masdevallias, draculas, stellis, pleurothallis, paphiopedilums,oncidiums, gongoras etc as seen in the photo below.

http://www.orchidboard.com/community...211730_283.jpg

Although it receives some natural lighting, it is reduced if I have to put the blinds down to block out direct sun and associated heat on hot days and possibly in winter (I just moved in, in Summer).

I was thinking of possibly using LED lights as they put out less heat and last longer. In particular I found: Ledvance LED Panel 32W (1200 x 300mm) - Tri Colour

New Tri Colour LED Panel Light 32W with 5 Year Warranty

and: Osram LED Panel 32W (1200 x 300mm) - Daylight 6500K

Osram Ledvance LED Panel Troffer 32W - 1200mm x 300mm

which could be suspended via these kits:
Osram Ledvance LED Panel Troffer Wire Suspension Kit


Having previously grown orchids and other plants in 3ft x 40cm areas - as well running 3ft freshwater planted aquariums - where I used up to 120W of fluorescent lighting, 30W doesnt seem like it would hardly be sufficient *but* it is LED so does that make a difference or is there a watt per area squared that I should be aiming for regardless of lightbulb type?

The height above the plants is a very important factor as well, but my suggestion is to keep looking.

Wattage, per se, is not a good selection factor. The type of LED, how it is driven, its PAR output and how its illumination is distributed are all factors.

I have illuminated a 180 cm x 90 cm area with two, 30 watt Philips Greenpower 120 cm linear LED Production Units, and a 120 cm x 46 cm shelf of paphs and phrags with 5 x 13W compact horizontal lamps (each one having a 4 cm x 160 cm emitting area).

Those panels you linked to are totally inappropriate for plant lights as they are "edge lit" indirect lighting panels. Yes, they may have "so many" watts of chips in them, but their output is into the thick white diffuser and not to the plants, so there is a HUGE reduction in the light actually radiated.

Obviously I cannot speak for all of them, but I once ordered a panel like that, and the chips are in the perimeter, "firing" inward, so the output is both reflected and diffused. It works fine to illuminate my work area, but if I wanted to use it for plants, the damned thing would have to be less than 15 cm above them.

Thought I would share a possibly relevant data point.

I bought a 4', 48W Koda shop light last December from Costco for about CA$50, thinking I could use it for plants. The PAR output was about 230 PAR at about 6 inches, checked using an MQ-500. At >= 12 inches, that will put the PAR output at only around 100 PAR if not less.

The Koda shop light is not as diffused as the edge lit panels posted in this thread and consumed more watts. Therefore, in theory, these panels, also being an indoor illumination light for human, will likely produce even less PAR, being at a lower wattage and having less concentrated light.

Now, according to Google, low-light orchids like phals only need a DLI of 4 [0], and 70 PAR at 16 hours a day [1] will achieve that. You might be ok with those panels if you put them no farther than 12 inches away from the plants and keep them running for long hours in a day. But, like Ray said, I would keep looking as well.

Hope this helps.

0: MechaTronix - Typical PPFD and DLI values per crop
1: 70 PAR * 16 hours * 3600 seconds in an hour / 1000000 (number of micromoles in a mole) = 4 moles

DLI (Daily Light Integral) Chart - Understand your plants' PPFD & phot – Ledtonic

this is another reference for achieving different DLI based on your PAR. phals are 4-6 and in my experience cattleyas range from 6-10. because LEDs give consistent light you can get away growing high light orchids with less overall intensity as well. I've been getting cattleyas to bloom with 150-200 par for 12 hours.

Thanks everybody for your feedback & info :)

Most of the commercial grow light units I can find online in Australia are geared towards providing high intense lighting for hydroponic 'crop' growers of a larger area or are ones meant for aquariums.

Given that I only want to light an area of 213cm x 47cm or almost 7ft x 1.5ft & I want to be able to sit at the table & be able to look over at the area without glare in my eyes I'm thinking of going with multiple individual lights using a combination of the following (varying depending on what bulb fitting type I get & what lampshade it will fit into):

Modern Metal Retro Style Ceiling Pendant Light Shade Lampshade Downlight Lamps

1.8M E27 Cable Cord Plug Pendant Lamp Light Bulb Holder Socket Base With Switch

along with bulbs such as

Full Spectrum Grow Light LED Bulb - 15W | Aluminium| E27 | IP55 | Stealth | Clone Light
&
Verbatim Outdoor IP65 LED PAR38 14W 5000K 1460LM

as I don't want the area to be completely under a purplish light.

I've read that there are newer full spectrum LEDs that don't produce that purplish light & alternately I could use a Mars Hydro SP-150 Full Spectrum LED Grow Bar - 150 Watt - Quantum Board but they only have a 2 year warranty & cover an area of 90cm x 45-60cm so I would need 2 & at $299.99 each but that's way more than I really wanted to spend!

Also the area does receive a good deal of varying natural sunlight coming in through the glass window/sliding door during the day so I may not need as much light compared to if the area were say in a basement.

http://www.orchidboard.com/community...218_173355.jpg

While it is preferred, I really don’t think it is necessary to stick to “plant lights”.

PAR incorporates the wavelengths from 400 to 700 nm. A plant light will have more of its energy toward the two ends, while a “people light” will have more in the middle, as that’s where plants and eyes absorb best, respectively, but they both incorporate pretty much all of that range of the spectrum, so they look white.

Plants want a certain number of photons per day in that range. While the specific spectrum within that range can play a role in plant growth and flowering, it usually does so only if it is greatly skewed.

I have found that decent quality LED floodlight bulbs for outdoor lighting are just fine. The key is to select lamps that direct the photons to the plants. I really like Cree 18 watt floods for that.

The Mars Hydro SP150 is probably an overkill for your application. It is insanely bright for human eyes and can be obnoxious. Many professional grow lights, including most quantum boards, designed for the production of medical plants are like that. You don’t want to be wearing shades in your living room. :)

May I suggest 2 ideas:

1. Track lights hung from ceiling coupled with spotlight bulbs, and you can direct the beams onto individual plants. The downside to this is that plants on lower shelves will not have much light.

2. Amazon(.com) has a good selection of low cost grow light bars, such as this one. While I don’t use these myself, I have heard people satisfied with the purchase. These lights are not overly bright for the eyes and are very flexible. The downside is that they need to be hung closer (15–30 cm) to the plants.

Edit: I agree regarding those burple lights. Their spectrum is not necessarily better for plants. However, the pink/purple glare is definitely bad for human eyes.

The practice of using blue & red LEDs came about with illicit pot growers.

Folks with "grows" in their basements - totally unseen by the outside world - were still discovered by the police due to their excessive electric bills for lighting. Switching to LEDs helped that, but using only red and blue that coincided with the peak uptake of chlorophyll meant that your watts had more "bang for the buck", as you weren't "wasting" electricity on the wavelengths in-between.

A pot grower couldn't care less what his plants looked like.

No contention, or disrespect, intended (by any means)... but, I think NASA & Cree were in the game long before the wacky-baccky farmers dived into the game on a broader scale.

NASA - LED Lights Used in Plant Growth Experiments for Deep Space Missions

That may very well be true, but the proliferation of those ugly lamps was driven by pot growers.