48" 4-bulb T5HO setup: question about bulbs

[007]

Hi Everyone,
This is my first posting....I'm new to the board. I have been reading through the threads and learning loads of valuable information. In fact I've read so much I'm feeling a bit overloaded at the moment !!!
I just set up a wire rack in my basement ( picture to follow once I read the instructions on how to do that!!). The rack has four shelves. I have hung a 4-bulb T5HO fixture above the top shelf. The plants are 18" below the fixture. I have a mixed group of Catteleya hybrids and species as well as a few Bc and a few dendrobiums. I hung another 4-bulb T5HO fixture below that with another shelf of plants about 24" below it. That shelf contains a mix of oncidiums, 2 phaps. 2 phrags.a few brassovola and a few other assorted species.

My question is about the type of bulbs that I have in my fixtures, and how close the plants should be to them.
I purchased the fixtures and the bulbs at Home Depot. The bulbs are 54Watts, 5000 lumens, cool white. The packaging on the bulbs also says the color temperature
is 4100K. Im not sure what that means! Since there area 4 bulbs in the fixtures will there be enough light? too much light? what about duration?

I live in Rhode Island and have grown orchids for several years in a greenhouse under natural light and almost all have thrived. I am moving my plants to artificial light because I turned the heat in my greenhouse way down this winter ( 45 degrees at night) to save on heating costs.

Any advise/help would be greatly appreciated. I am so thankful to have found this site!!!

Many thanks!
Sean

[billc]

Hi Sean, Most use use 6400K CRI bulbs as they are closest to natural light. Some folks mix in 3000K bulbs which give more of the red spectrum for blooming. I've tried that but it didn't seem to make much of a difference for my plants.
Are the distances you are giving from the top of the leaves to the lights or from the shelf to the lights? The plants will let you know if they are getting too much or too little light. You are better off starting further away and moving them closer as you figure out the light. Less chance of burning the leaves that way.
I have mostly paphs and phals under T5's and I run the lights 8 to 9 hours a day.

Welcome and good luck, Bill

[007]

Hi Bill,
Thank you for your help! The distances I mentioned (18' and 24") are the distances from the shelf to the lights. Some of the leaves on the plants ( especially some of the taller Catts) are almost touching the bulbs.
I think I will try lowering the shelves a bit at least on the shelf that is closer to the fixture. I am also going to set up another shelf unit with two more fixtures since I have a few more plants that won't fit into my current set up. I'll increase the distance of the shelves from the lights on the new set up so I have different light level options to choose from.

I am still a bit confused about the light bulbs. When you say most people use 6400K CRI bulbs is that lumens? or is it the "color temperature" as was listed on the side of my light bulb packaging. Mine said 5000 lumens and 4100K color temperature...so confusing!! Are the 6400 bulbs "warm white" rather than "cool white"?
I guess I will need to order my bulbs from a specialty supply store. The bulbs I bought from Home Depot were cheaper by the case ( $88 for a case of 15 vs. $9.89 per each when purchased one at a time). Where did you purchase your 6400K bulbs?

Sorry for all the questions!! I want to make sure my plants are happy in the basement!! They are used to a nice humid greenhouse!!

Thanks!
Sean

[Subrosa]

The "k" value and the "CRI" of a bulb are two different means of measuring the color spectrum. "CRI" stands for color rendition index, and is given as a %. A CRI of 90 means that the color rendition of the light reflected off of an object is 90% true to that of natural sunlight by whatever means they measure it. It's more a measure of esthetics than performance. The "k" number is the color temp in degrees Kelvin, and is a more objective means of measuring light spectra. It refers to the color of light given off by a black body object at that specific temperature. This is a long winded way of saying that the term "6400k cri" is a meaningless mixture of 2 standards. 6400k light is very close to sunlight at sea level, but has no direct bearing upon the cri of the specific bulb.

[billc]

Subrosa, I knew that didn't sound right when I wrote it early this morning, I have to remember to finish my first cup of coffee before thinking.
Sean, Lots of places online sell the bulbs. I usually pick them up at a local hydroponics store. You could certainly get by for a while using the bulbs you have. Years ago I was able to bloom most of my plants with T12's and never paid attention to what kind of bulbs they were. Ignorance is bliss.

Bill

[007]

Subrosa,
Thank you for explaining that! It is going to take me a while to learn the ins and outs of growing under lights!

In my greenhouse I didn't have to do much for my plants other than keep an eye on their repotting cycles and keeping them fed!! They thrived in the humidity and the light seemed to be perfect for almost all the plants I attempted to grow ( species paphs being the exception..they are a real challange for me!!...maybe I'll have better luck under lights!!)

Thanks,
Sean

---------- Post added at 06:35 PM ---------- Previous post was at 06:10 PM ----------

Bill,
I will start searching on line tonight for the 6400 CRI and 3000K bulbs. I might try using the existing bulbs I have since they came 15 to the case!! Maybe they will work well for providing a lower light option or I could mix another kind of bulb in with them ...maybe two of the 5000 bulbs I have with say two 6400 CRI bulbs?...I'm a little leary of doing anything different than what folks on the board have found to work well.

Thanks for your help!
Sean

[Ray]

The only problem with the use of color temperatures with fluorescents is that they are not black body radiators, so the temp may-, or may not really describe the spectrum.

In fluorescents and LEDs, you are getting a correlated color temperature, that is, the phosphor blend is designed to appear to the human eye to match the true color temperature. So, while that 4100°K tube may be chosen thinking that it provides more red to help with blooming, in fact it might simply have less blue and not more red. That is why it is better to look for fluorescent bulbs that are intended specifically for plants, as they - if produced by a reputable firm - will have a phosphor blend that does give a good spectrum of light output.

Sean - there is no such thing as a "6400 CRI". As was stated in the comments above, Color Rendering (or rendition) Index is a descriptor of how well the color reflected to the eye matches that if the light source was natural sunlight, and is a percentage, i.e., has a maximum value of 100.

[007]

Thanks Ray,
I think the message here, if I am correct, is to purchase bulbs made specifically for plants. Bulbs manufactured specifically for plants should have the correct amount of both red and blue spectrum that the plants will need to produce vegetative growth and flowers. Is that correct?
Now, assuming that is correct, is it possible to purchase 48" T5HO bulbs made specifically for plants? If so, is there a specific bulb that is recommended ?

Thank you again (everyone) for taking the time to help out a beginner!!

Sean

[Ray]

Originally Posted by 007

Thanks Ray,
I think the message here, if I am correct, is to purchase bulbs made specifically for plants. Bulbs manufactured specifically for plants should have the correct amount of both red and blue spectrum that the plants will need to produce vegetative growth and flowers. Is that correct?
Now, assuming that is correct, is it possible to purchase 48" T5HO bulbs made specifically for plants? If so, is there a specific bulb that is recommended ?

Thank you again (everyone) for taking the time to help out a beginner!!

Sean

I hav grown and bloomed many plants under Hydrofarm T5HO fixtures. They come with 6400°K bulbs.

Check out Hydrofarm.com, and drop me an email. I am a discount reseller of their stuff, and can usually chop at least 10-15% off of their MSRPs

[007]

Ray,
Thanks. I'll check it out!
Sean