all flurescents have the exact same spectrum

The vast majority of triphosphor fluorescents have exactly what you describe, the same three clumps of blue, blue-green, and red wavelengths, in different combinations. These are the 830/841/865 fluorescents which form much of the market today.

The expensive 950/965 type fluorescents are also based on the same three phosphors but they have additional phosphors to produce more light at other wavelengths. It might not be very obvious on your spectrometer as the three primary peaks may still appear dominant.

The old halophosphate (eg. 540) fluorescents have a quite different spectrum. Try to get hold of one of those and you'll see it isn't based on the same three wavelengths at all.

Other fun tubes to look at would be the actinics and the plant/aquarium tubes, obviously quite different. Metal halide, HPS, and LPS (low pressure sodium, the very yellow street lighting in some areas) are also instructive to look at. And mercury vapour lamps (again, some street lighting, quite a blue-white colour) are fun.

Very interesting Shrub.

This weekend I'm going to see if I can buy a TRUELITE 13$ and an AGROSUN 24$ and look at the diffrence in spectrum.
This should be very interesting to see why they charge so much for a flurescent tube.
My guess is I won't see a big diffrence if a diffrence exist.
I will also bring my spectrometer and camera to the hydroponic shop and try to get the spectrum for HPS, MH and the T5 Tek lights.
These guys are usually not very friendly... probably because most of the customers are not into growing peppers...

The phosphors in the Truelite and the Agrosun fluorescents are virtually identical. The rest is just marketing.

I took pictures of the spectrum for 6500K 5000K and 3000K lights.
No use in posting all of them since they are all exactly the same.
You can't see it in the picture but I could see faint bands all the way to around 720nm plus or minus 10.
Unfortunately my crude spectrometer does not tell me the intensity of each band.

The red triphosphor produces its main peak at 611nm but also minor peaks right out to 712nm. I guess this is what you are seeing. You can see lots of emission lines on your spectrum, but the main red, green (double), and blue lines are orders of magnitude more intense and contribute the vast majority of the light. Some of the far blue lines are probably direct mercury vapour emission.

From the results I got, I'm really starting to doubt the common knowledge that a 6500K will increase vegetative growth and that a 3000K will promote flowering.

>

My hypothesis is that the differences between using a 6500K vs a 3000K will be insignificant.

Of course this is for Fluros only.
HPS and MH are very different because the chemical nature of each lamp is very different and the spectrum of these lights must be significantly different.

Shrub, I hope Im not boring you with archaic experiments and hypothesis. IÂve already read through the entire forum. Of course I forgot 90% of what I read. :(
In any case the fun part of a hobby are discussions, experimenting and theorizing.
So IÂm having a blast with my newly found hobby!

My hypothesis is that the differences between using a 6500K vs a 3000K will be insignificant.

Although the wavelengths being emitted are the same ones, the proportions emitted at each wavelength vary significantly. It might not be readily visible on your spectrometer but the amount of blue emitted by a 6500K fluorescent is many times greater than that emitted by a 3000K.

You can think of a triphosphor fluorescent as like 3 LEDs, a red one, a green one, and a blue one. All three together produce a white light. A "3000K" light would have the blue LED hardly on at all and the light would be orange. Look at a 3000K fluorescent next to a 6500K fluorescent and the difference is striking. Plants need a certain amount of blue wavelengths to grow healthily. The exact amount seems to vary with different plants, but in general the amount of blue light given off by a 3000K fluorescent is not enough, while the amount given off by a 6500K fluorescent is plenty. The rule of thumb used to be a mix of warm white (3000K) and cool white (4100K) and it seems to work for seedling veggies and annuals. For the cacti and succulents that I grow, a mix of 4100K and 6500K works better, too little blue and the plants tend to grow a very plump lush green which is not always healthy for a cactus.

The old "blue for growth" and "red for flowering" adages are gross simplifications. For one thing, the "red" and "blue" lights referred to both produce a large proportion of their output in the red wavelengths, and most plants will grow quite happily without about 90% of their light coming in the red wavelengths. But when the proportion of blue drops too low, the plants start to stretch, may start to produce "shade" type leaves, or may stop growing and start to flower instead. When the high output lamp choices used for "serious" growing were limited to HPS and metal halide, the simple one or the other decision made sense, but today we have a much wider range of options.

Lastly, be cautious about a lot of what you read on the internet. Half of it is written by people who are stoned out of their mind (the "whoah, that's bright man" brigade!) and most of the rest by aquarium owners who have some very different lighting needs from regular plant growers.

Shrub,
I'm still not convinced of the benefits of mixing a cool white 6500K with a warm white 3000k.
Before I did the spectrums, I was expecting a different spectrum from the 6500K and the 3000K or at least a very big difference in the intensity of reds and blues.

The cool white hits the sweet spot for the blue light wave but does not do very good for red waves.
The spectrum of a 6500K is the same exact same as the 3000K with the only difference in intensity of blue an red.
Even if the 3000K gives out more red, it's only giving out more red light in the poor absorption part of the spectrum.
True that plants will benefit from the extra red light even if it's not at the sweet spot but the gain will only be marginal and not very efficient.
Also since you are switching a 6500K with a 3000K you provide less "sweet spot blue growing light" .

The sweet spot for reds is about 640nm to 680nm.
The spectrum of the fluros shows that the bulk of the red light ends approx at 625-630nm and very little light is produce in the 640-680 range(sweet spot).

The Sylvania Gro-Lux (not the wide spectrum but the normal Gro-Lux)is very interesting.
Those light produce lost of red light at the sweet spot part of the spectrum for plants.
But they also do poorly in the blue spectrum.

From the theoretical data, a mix of Sylvania Gro-Lux and any cool white 6500K should come out a winner.
I think even mixing incandescent lights (lots of reds wavelength) and some cool white should do better the mix of cool and warm white.

I was expecting a different spectrum from the 6500K and the 3000K or at least a very big difference in the intensity of reds and blues.

Nope, spectrum is the same. Relative intensity of the reds and blues is the only difference. Since your spectrometer has no intensity scale you can't really see it very well, but a 3000K triphosphor has a red peak at about double the intensity of the main blue peak. With the 6500K, the blue peak is about double the intensity of the red peak. I'd call that a big difference. You can find some fluorescent spectra on the net which include an accurate intensity scale, even some for the individual phosphors. Be cautious, some spectra that include a scale do things like averaging over a few tens of nanometers so that the peaks get smoothed out. Those triphosphor peaks really are pretty narrow.

True that plants will benefit from the extra red light even if it's not at the sweet spot but the gain will only be marginal and not very efficient.

And yet that red light works. Maybe there is something wrong with the "sweet spot" theory? In fact there is nothing wrong with the theory, just that most people are using the wrong theory! The bad theory says that plants photosynthesize using chlorophyll therefore light which is not absorbed by cholorophyll is useless, I'm sure you've seen the graphs I'm talking about. Chlorophyll absorbs light shorter than about 630nm very poorly and hence the theory runs that the standard red phposphor is virtually useless. This theory is heavily pushed by many people with an agenda (eg. sellers of expensive lamps and people who spent a lot of money on expensive lamps), but it is wrong. Plants contain a whole array of different pigments, some of which use light directly, and some of which absorb light and pass it on to the chlorophyll. The actual range of wavelengths useful to plants is represented (approximately, since it is a little different for every species) by the photosynthesis action spectrum, in which the "worst" green light is roughly half as efficient as the "best" red light. The 610nm-ish wavelneghts emitted by the standard red phosphor are about 80% as efficient as the best possible red wavelengths, and roughly as effective as the best blue wavelengths.

The thorough wrongness of the chlorophyll spectrum theory is shown by HPS. HPS lamps produce light in almost exactly the wrong wavelengths for chlorophyll but in fact plants grow rather well under them. They are extensively used by commercial growers, partly for legacy reasons but mainly because they are the most efficient light source available (excluding LPS). Commercial growers are well worth listening to because they have real money at stake, a pretty strong incentive to get it right. HPS is perfectly suitable for many growing tasks, even better when supplemented with natural light for a little extra width on the spectrum, but occasionally supplemented by a more blue light even by commercial growers.

Those light produce lost of red light at the sweet spot part of the spectrum for plants.

That's the whole idea. They use a different red phosphor to produce a longer wavelength red light. Theoretically more efficient than the standard triphosphor but not the radical difference that some advertising might have you believe. Add in short lifetimes, poor lumen maintenance, slightly lower overall efficiencies (although not as bad as the lumen numbers suggest), and the high cost, and you have many reasons not to use this type of fluorescent. It is usually easier and more cost-effective just to use more light out of standard triphosphor tubes to offset any differences caused by the spectrum.

But they also do poorly in the blue spectrum.

Yes, not a whole lot of blue in the original Gro-Lux. Hence the pink colour rather than the purple you get with the wide spectrum Gro-Lux which has quite a bit more blue. Theoretically it has sufficient blue for typical plants (eg. lettuce or petunias) to grow perfectly well but some people were not happy with it. I suspect the aquarium crowd, who have a legitimate need for more blue light, were part of the reason for more blue in the wide spectrum version. Strangely enough, the wide spectrum Gro-Lux has an extremely sharp peak in the blue, although the red peak is indeed very wide reaching basically all the way to green.

I think even mixing incandescent lights (lots of reds wavelength) and some cool white should do better the mix of cool and warm white.

And yet it doesn't. Using the right theory shows part of the reason. Another part of the reason related to the heat production of incandescents and the associated balance of infra-red light. A number of plant functions are controlled very specifically by the balance of light at certain infra-red wavelengths and the visible red wavelengths and incandescents really mess this up. Incidentally, there are specialist fluorescents available which mimic an incandescent spectrum with the efficiency of a fluorescent, although they don't produce the wavelengths as far out into the infra-red that you get from an incandescent.

Much of the things we are discussing have been the subject of many experiments, originally using various filters and more recently using virtually monochromatic LEDs. The LED experiments show that red:blue LED ratios of around 10:1 work perfectly well for most leafy plants.

I'll mention again those pothead growers who have a lot to say about lights on the internet. They are growing a crop which, like cacti, has a greater need for blue and UV than the vast majority of plants, those higher energy wavelengths are necessary to synthesize alkaloids. Aquarium guys are just the same, they need blue light for all sorts of reasons: lighting up coral; seawater plants and animals that thrive on the blue; just to penetrate the water because red light is scattered; and simply because blue looks better in a tank. Don't be fooled by all that these vociferous groups write into thinking that regular green leafy plants need a 20,000K actinic shining on them :)

Ok I retract my statement! I was wrong. A mix of warm and cool white can be useful.
Like you said, the confusion came from looking at the wrong chart.
The graph of the absorption of chlorophyll is very misleading.

The graph that we really should be concern with is the photosynthetic activity.

Hey guys,

Old member, returning for a look. I like how the group knowledge is maturing -great posts now!

Question, I searched the archives and didn't see where I can buy a spectrometer. Where did you get yours and how much was it?

Thanks

Scott

It's a crude spectrometer but very fun and cheap.
Plastic Spectrometer

Hailed as "one of the very best, affordable scientific instruments" by the Astronomical Society Pacific, the Project STAR spectrometer is made of high-impact plastic for years of classroom service and comes completely assembled. The spectrometer uses high-dispersion, high-efficiency diffraction grating that produces an easily-read bright spectrum. Includes a reference label for bright spectral lines and a scale labeled in both electron volts and nanometers for chemistry and physics instruction. Also includes a 10-page activity booklet. The activities include:
Observing what diffraction grating does identifying various light sources identifying elements in flame spectra, solar spectra and street lights including mercury, sodium, hydrogen and neon.

http://www.starlab.com/psprod.html

Hey thanks.
Is there any reason one shouldn't get the $9 one above it?

Scott

>>Is there any reason one shouldn't get the $9 one above it?It uses the same component for analysing the spectrum. The only diffrence is that you must assemble it and it's made of cardboard instead of plastic.

I don't think it does use the same component. I think it is an inferior grating with lower resolution, although I may be wrong.

Check out this link. It's got lots of great light spectrum.

i think I finally found what I need for lights.
400 watts Galaxy Digital ballast + Agrosun® Red Reflector Lamp
(This is not the best lamp but witht the integrated reflector I will save a few $$ and I have limited space for a big reflector).
I will complement the light with a 54 watts T5 03 actinic fluoro lamp.
I willl also experiment with a 2' T5 Black light.From what i've read that UV can help produce more oils in plants.
I grow hot peppers and herbs (basil,sage,oregano...)

with all this analysis my poor laymans head says 'go with inexpensive 6500' for see starting. thanks for all the info.

my poor laymans head says 'go with inexpensive 6500' for see starting

That's what I use :)