If you post this question in the orchid forum you will get more responses. They are very knowledgeable about growing orchids under lights.

Good luck - Brooke

I like your style. Plus what indeed :) The Philips Cool White Plus is a high-spec triphosphor tube providing very long life, excellent lumen maintenance, good CRI, and good light output. You would not need to replace this tube every 6 months, you can run it to failure which should take over 5 years.

Soft white tubes are not considered suitable for plant lights except possibly in combination with cool white or daylight tubes. A cool white tube actually produces more red light than blue, and in exactly the same wavelengths as the soft white (=warm white) tube. So you don't need a separate tube to be getting red wavelengths unless you actually want more of the red wavelengths, which may encourage flowering.

Philips produces a great many tubes tagged as daylight. Some are better than others. All will produce a spectrum with somewhat more blue and somewhat less red than the cool white.

As to whether you need a specialist tube, that is something only you can really decide. Some people claim the plant tubes are better, some say the regular ones are just as good. One thing you will find is that the Philips Plus range of tubes do not provide colour rendering equal to natural light, you may find that the plant colours are slightly grey. Some shades in particular may become almost invisible. Of course the funny pinky-purple plant lights don't render colours properly either!

I called Philips and got them to send me spectral energy distribution data for all of these bulbs. The soft white shows exactly the same blue peak values as the cool white, but slightly higher values for the red peak. So it may be worth using. They also sent an article describing a study of plant growth under their plant and aquarium bulbs compared to another brand plant-growing bulb having wide spectrum, and to cool white plus incandescent. Needless to say, their P&A bulb won. But their power distribution did look pretty good when matched against plant 'needs'. While the cost is 3x that for cool white/soft white the power output also is about 3x at red and blue wavelengths. I don't know whether their bulb life figures are reliable; the T12 P&A bulb says 20,000 hours while the T8 cool and soft whites say you keep about 90%+ of the output at 30,000 hours, using a timer.

Thanks for the comments.

matched against plant 'needs'

Take this with a pinch of salt. The basic idea is sound but the chlorophyll absorption spectrum that light manufacturers usually show does not really represent a plant's light needs. Actual plants photosynthesise more or less half as efficiently with green light as with the perfect red or blue wavelength, not the five or more times shown on the chlorophyll graph. And if you provide an enclosed environment to bounce the light back at the plants then they get more chances to use the reflected green light, so eventually it can all get photosynthesised. This is just one of many reasons why experiences under P&A lights vary from very good to the same or even worse than a cool white.

The spectral graphs show what I was trying to describe in words. Peaks at exactly the same wavelengths but the warm whites have a higher proportion of their light in the red peak and a lower proportion in the blue peak, hence a bit more reddish coloured. For most plants, the proportion of blue light from a warm white fluorescent is lower than ideal for producing strong compact growth, while a cool white or a mix of cool white and warm white gives a good proportion. I grow succulents and cacti and like to use "daylight" fluorescents which have an even higher proportion in the blue peak.

Hello everyone,

shrubs_n_bulbs : Maybe it's me misunderstanding, but you seem to be contradicting yourself, hence confusing poor people like me...

In your first post, you write :
> "A cool white tube actually produces more red light than blue, and in exactly the same wavelengths as the soft white (=warm white) tube"
And in your second post, you then write:
> "but the warm whites have a higher proportion of their light in the red peak and a lower proportion in the blue peak"
Can you please specify if you were just confused and which one is right of the two; or if you were coherent and then explain the subtility a bit better? Thanks.

rockyfarm : Is there any way that you could share those Philips spectral energy distribution data graphs with us? Or are they already alvailable somewhere on the Web, like Philips website?

Finally: I've seen the new Ecolux series from GE, and they also have a P&A bulb that is really cheap ($5 for a 48"). Anyone got info on that one or the series (cool/warm/daylight)?

Thanks to anyone who can help.

-ChrisL.

I am having good growth & fruit production, using a combination of CFL's. I alternate 5600K & 2700K in reflectors, leaving on with a timer about 18 hrs a day. Any comments ?
Also, I am curious : I installed a non-vented gas wall heater to my unheated 14X24 hot tub / grow room. It's a Vangard Glo Warm, 20,000 BTU. Will the fumes affect my grow opperation ? I leave a window open a couple of inches for fresh air