LED fixture questions
 

I recently purchased a 300 watt Mars Hydro LED fixture on ebay. I seems really bright, and I'm unsure how close this thing needs to be to my plants. I keep mostly Dendrobiums, Cattleyas, and other species that prefer medium to high light levels. I'm currently also using T5 fluorescent fixtures, and 4-6 inches from the bulbs seems to be the right distance for most of my orchids. The LED seems a bit brighter though, so I'm hesitant to put my plants that close. I've included the link to the ebay listing for this grow light in case any of the included details would help anyone in advising me.

Mars Hydro 300 Full Spectrum LED Grow Light 140W True Watt for Indoor VEG Flower | eBay

It can be hard enough to burn your plants, do not know. Try initially at least 2 foot and see how plants react. By changing the type of light will react, pay attention to the type of reaction.

well it is designed for growing a very popular herb so it is very bright from what ive read, so id try it a few feet away as the poster above said.

This video may help you:

https://www.youtube.com/watch?v=Ymt1XCCu-RM

At 24", he measured 272 micro mol/m^2/s. Yours is a discontinued model, which is quite less efficient than Mars II, which is tested in the video. So I'm guessing that you'll be getting around 200 micromol/m^2/s at 24". It is probably a good starting point for Catts. Full sun at noon time is around 2000 micromol/m^2/s.

I don't have any experience with their products, but I hear quite a few people had issues with their products, but I hope that yours will last long.

Disclaimer: please take everything presented here as anecdotal. This is what happens when you grow the exact plants I grow under my exact conditions. I have similar fixtures for wintering my plants that require/can tolerate cold but not freezing temps, and mainly those that require high light levels. The area is 2' x 4' x about 3' high. I use 2 fixtures which use the same brand and type of emitters, although they're designed for reef tank usage. The emitters are advertised as a mix of 10,000K and actinic blues. Total output on your fixture is 140W, and on each of mine 120W. At approximately 4" away from the fixtures, an app which measures light intensity in lux gives a reading around 4400. At this distance, orchid- wise, I have Dendrobium kingianum, D. speciosum, D. parishii, D. aggregatum, and my Cymbidium plants. These plants spend as much time as weather permits outside in direct sun from a bit past sunrise to mid afternoon, so they are well acclimated to very high light levels. I don't need to worry about acclimating them to high light until I put them out again in the spring. At 6" to 8" I have my Fukiran. They're fairly shaded by other plants while outside, so this could be an increase in intensity. That's the hope anyway. At a bit over 2', but heavily shaded is an Oeceoclades maculata. The plants have been under these conditions for about a month. All plants look good. D. kingianum and aggregatum had new growths underway when they came in, which have developed nicely under this regimen. And my Cymbidium goeringii 'Lian Ban' has developed what appears to be a spike since arriving around the same time.

Subrosa, so you have your Dendrobiums 4 inches from the LED? And they don't burn? I think I'll start with the fixture a couple of feet away, and move it a little closer to the plants every week or so. Like I said, most of my orchids prefer high light, so I'd like to give them as much light as possible short of burning them.

Not a sign of burn. Last winter I had the same plants about 1"-2" away from T5HO tubes, and the leaves on the speciosum turned a nice reddish color. No sign of a suntan yet this year.

I have been looking everywhere for data like this for my leds. Thanks for posting.