Lighting "experts" please respond, the kelvin issue - Orchid Board

HereticHammer · #1 (**permalink**) 04-22-2009, 12:19 AM

I am getting a new T5 lighting fixture and had a choice of either all 3000k lamps, all 6700k lamps or a mix of the two. I went with a mix of the two but I really want to hear strong arguments from all sides of this issue so I can be better informed when I replace the bulbs in a year.

This thread is for all those who have some knowledge on kelvin temps and plant growth and flowering to share that knowledge with us, pro and con, so we can make up our own mind.

I have heard MANY say that they are growing AND blooming plants just great under all higher kelvin (6400k, 6500k, 6700k) bulbs. I hear just as many that swear by mixed lamps (3000k and 6700k.)

I also know that there are those that say that you need a mix of bulbs because the lower kelvin is for blooming and the higher for growth but if orchid growers can grow AND bloom plants under higher kelvin lamps, why do we need the lower ones?

Is there any solid science to all this?

Ok, lets here it.

TeresaE · #2 (**permalink**) 04-24-2009, 07:21 PM

Oh gosh, I bought my T5 lights a few years ago...have some mounts under on T5 and a bunch of Catts under two T5 lights. I can bloom everything. They are great. But I think the wattage is the lower number. I flower cats under one fiture with a regular "bright" 40W bulb and a special grow light that is supposed to have a 4 year life....bought it at a hyponics store. Bloom Catts under these too. I think it really depends on a combination of lights, watering & fert. Try different things and see what you have success with. Trust me on that.

HereticHammer · #3 (**permalink**) 04-25-2009, 04:29 AM

If you mean by "lower watts", the lower kelvin (which is temperature) then you would be talking about the 3000 Kelvin temp. You can tell if that is the case because the light should be more yellow to your eye if I am write about that temps color.

The watts don't effect the kelvin rating and you can get both 3000k and 6700k in all the watt power sizes.

calvin_orchidL · #4 (**permalink**) 04-25-2009, 08:45 PM

I use mixed bulbs, with no natural sunlight, and things bloom. I believe others only use the higher temperature bulbs and things work as well. There were a few huge discussions on this topic and no one can seem to agree on what is the best combination to use. I have heard that the high/low temperature for growth/flowering is not too applicable to orchids...this belief originates from another type of popular horticultural practice in which flowering is initiated by the change in light temperature as well as duration.

phearamedusa · #5 (**permalink**) 04-25-2009, 08:57 PM

HereticHammer,

Kelvin refers to the light color rendition, the higher the kelvin rating the bluer the light, the lower the rating the more orange the light.

Full, or daylight spectrum is 6400k to 6700k depending on manufacturer, and can be used for optimal vegetative growth. The color of your flowers will look like it should.
Blooming bulbs tend to be in 2500k to 3500k range. They have a reddish glow, colors will NOT be true. Plants grown under a blooming bulb during vegetative cycle may have longer internode spacing, but it doesn't harm them.
Hope this helps.
Melanie

phearamedusa · #6 (**permalink**) 04-25-2009, 09:40 PM

Quote:

Originally Posted by calvin_orchidL

I use mixed bulbs, with no natural sunlight, and things bloom. I believe others only use the higher temperature bulbs and things work as well. There were a few huge discussions on this topic and no one can seem to agree on what is the best combination to use. I have heard that the high/low temperature for growth/flowering is not too applicable to orchids...this belief originates from another type of popular horticultural practice in which flowering is initiated by the change in light temperature as well as duration.

The reason most growers of the other horticultural group use High Pressure Sodium bulbs has to do with the lumen output these bulbs have vs. Metal Halide. HPS have higher lumen output, and last twice as long as MH bulbs. Some growers will only use HPS bulbs. Flowering is initiated by the change in day night length, not the color spectrum of the bulb. They can flower under MH just the same, but the results are better under the higher red spectrum bulbs. As I stated in my previous post blue spectrum gets you tighter internodes in the growth stage, while red spectrum is more for the blooming stage, but that you could do both under either one with no ill effects to the plant.

For example: Poinsettia are photosensitive plants, in the vegetative state, they are just green plants. Flowering is initiated by them getting 12hrs of light, and 12 hours of absolute darkness, and takes about 6 to 8 weeks of this light cycle, if memory serves me right. If I had two plants exactly the same, one grown under 6400K light, one under 3000K light during the veg state. The one under the 3000K light will appear stretchy in comparison to the one under 6400K. It will make no difference to the flowering of the plants or the quality of the plants.

Sorry for the long post again.
Melanie

s1214215 · #7 (**permalink**) 04-26-2009, 01:54 AM

I am using a mix of the two different kelvins similar in temp to yours. So far, all looks good. Many other growers use a mix of the kelvins like you have.

Some use only 6000 range too. I think Melanie has given you good advice. I would use the mix you have now.

Brett

s1214215 · #8 (**permalink**) 04-26-2009, 01:55 AM

I am using a mix of the two different kelvins similar in temp to yours. So far, all looks good. Many other growers use a mix of the kelvins like you have.

Some use only 6000 range too. I think Melanie has given you good advice. I would use the mix you have now.

Brett

quiltergal · #9 (**permalink**) 04-26-2009, 02:20 AM

Quote:

Originally Posted by calvin_orchidL

I use mixed bulbs, with no natural sunlight, and things bloom. I believe others only use the higher temperature bulbs and things work as well. There were a few huge discussions on this topic and no one can seem to agree on what is the best combination to use. I have heard that the high/low temperature for growth/flowering is not too applicable to orchids...this belief originates from another type of popular horticultural practice in which flowering is initiated by the change in light temperature as well as duration.

Calvin you kill me! Do those bulbs come with complimentary Zig-Zag papers?

As you can see Jonny you're not getting much solid science here. However, to my way of thinking personal experience seems in application just as good. My belief is that orchids aren't as picky about the color temperature of their light as some other plants may be as Calvin pointed out. I think you can successfully grow and bloom them under 6500s or 5000s with no noticable difference between the two except for how the flowers appear to your eye.

Here is a picture of my bottom shelf with 2 48" 6500K bulbs. The picture was taken about a month ago.

TeresaE · #10 (**permalink**) 04-26-2009, 02:46 AM

I used a MH bulb in the past and it sucked. Never flowered a single thing. Switched to fluorescent and since I can get the plants closer to the bulb I've had plenty of success. Wish I could grow under HPS but the bulbs are more expensive and also use more energy. I'm pretty sure there are pictures posted of my plant shelves I put here a year or so ago. I'll try and post "updated" pictures".