dull days

[katrina]

It likely won't burn your plants but it's too "blue" for anything except deeper water plants/life. W/the 18,000 k lighting (called actinic) you get more of the blue spectrum due to the needs of corals and other plants/life living in deeper water. Reds/yellows/greens do not penetrate deep water as well as the blue/violet end of the spectrum so anything living in deeper waters evolved to need that K factor. As a matter of fact, that K factor is geared for salt water plants/life which lives in deeper water and there's a strong chance that freshwater plants wouldn't even do all that well w/it. (My years of aquariums and raising fish comes in handy from time to time. )

If you need the extra light then your best bet...if using just one or even two bulbs...is to go w/something closer to natural daylight - 6500k - which gives a good mix of red and blue. This will give you a better balance of the light spectrums needed by orchids.

[Nexogen]

Excuse me.
K is useless when used for plant growth lamp (useful only to the human eye - that is how we see the plant).

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

[Nexogen]

To be more eloquent and with the permission of iGROW, see in the image below about how things are.

However the problem is more complex but is rather short as seen in the graphic.

[katrina]

Originally Posted by Nexogen

Excuse me.
K is useless when used for plant growth lamp (useful only to the human eye - that is how we see the plant).

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

True, true...but many of us are not as educated in all factors that are light related and for ease of purposes...Kelvin can be and is a very good starting point for someone just getting started into all that goes along w/lighting (not LED related of course) for orchids/plants. Kelvin can and does denotes the red/blue/yellow factor and that basic knowledge is all one needs to successfully grow and bloom an orchid under fluorescent lights. Not all of us strive to obtain a PHD in lighting. Just saying.

Plus, the OP asked about 18,000 kelvin light.

[phalnoob]

Thanks for the replys i will check out thise links and read up some more.
I kept fish for years always wanted a marine tank but was too scared to do it!
As iv said i just want to do the right thing so they all grow and thrive, and so wanted just a simple easy setup to supplement on dull and winter days. I got a very sad looking spider plant for pennies at a garden centre and in my north facing window sill after only 3 weeks its got loads of new leaves and even a baby plant starting so happy days

[wintergirl]

I just bought cheap plant growlights and hung them under shelves. I am able to bloom cattleyas under them in a North window, so I must be doing something right and it didn't cost an arm or leg.

[phalnoob]

Thanks fo u happen to have any details for your setup and what grow lights. Just out of interest if you have a moment.
Thanks

[wintergirl]

I went to Walmart and bought these Under cabinet type of grow light. They are about $12. (I don't see them online but they are in store). I took the plastic cover off the fixture, so the bulb is open. Then I hung them with wire from the shelf above. On my catts I have 3 of them together. I use them for my other orchids as well. One time I went to the store and they were out of the grow lights, but just had the same light fixture with just a regular bulb. I bought that and bought a fluorescent plant light bulb and put it on there. It is slightly bigger than the one that comes included in the complete setup but still works.
Here is an older picture of my set up at dusk.


The cords are off to one side and they just go down and plug into a power strip below the rack. I have clear plastic on my shelves so no water gets on the lights.

[phalnoob]

Thanks. Wow that looks awesome!