GE9325K bulbs are not "pink" grow bulbs...

[Splash]

I've been doing some study lately of PC bulbs and their spectra. From what I have seen, there appear to be only three rare-earth phosphors used in PC bulbs. Divalent europium has emission peaks in the blue and violet, with the highest peak arround 440 nm. Trivalent terbium peaks mainly in the green at 540-550 nm, with several much smaller peaks at 480 nm, 575 nm and 620 nm. Lastly, trivalent europium peaks mainly in the red, around 615 nm, with much smaller side peaks at 590 nm, 650 nm, and 680 nm. All of the fluorescent bulbs commonly used in aquaria (other than actinic) seem to be simple mixes of these three phosphors. Phosphor mixes with more of the higher wavelength (i.e., red) emitter have low blackbody temps (~5000K), and phosphor mixes with more of the low wavelength (blue) emitter have higher blackbody temps (~10,000K).

In terms of plant growth, the green-emission phosphor is largely wasted, because it peaks at 550 nm, which is the lowest point in the photosynthetic action spectrum for green plant pigments. The red plant pigments do absorb energy in this region, so too much green light can make your green plants add more reddish pigments (e.g., Crypts turn from green to bronze). The red-emission phosphor is also largely wasted because it peaks at 615 nm, which is also a region of low photosynthetic activity. The red "sweet spot" for photosynthesis is way up at 660-680 nm. The blue-emission phosphor actually hits the other photosynthetic "sweet spot" around 440 nm. This phosphor gives the most bang for the buck.

So why use the green- and red-emission phosphors? The answer to that involves the photopic curve, which describes the spectral response of the human eye. The photopic curve is very close to Gaussian, with a peak around 560 nm and falling to zero at 400 nm and 700 nm. It is skewed ever so slightly and drops a bit more quickly on the blue side of the spectrum. So the green- and red-emission phosphors aren't really there for plant growth, they are there to provide brightness and color to the human eye. Interestingly, light from the blue-emission phosphor is very poorly perceived by the human eye, but this is the one that really drives plant growth. Which finally brings me to the subject of...

The GE 9325K bulbs use the same three phosphors as described, but really increase the amount of blue-emission and red-emission at the expense of the green-emission. The 9325K designation would indicate that the bulb is shifted toward the blue end of the spectrum, yet the bulb looks pink. That's because the human eye cannot perceive the 440-nm blue light of the divalent europium phosphor.

SUMMARY: IMHO, the GE 9325K bulb is a good grow bulb because it has a lot of BLUE light. It looks pink because it has more red light than green light, and the human eye can't perceive the blue light. Neither the red light nor the green light contribute as much to photsynthesis as the blue light.

[Rolo]

Intriguing! Nice report splash. I've always wanted too know exactly about the "magic" of these bulbs. Where did you find the statistics about the GE 9325K bulb, and it this the PC or NO type? Can you give a few good site or other resources about light spectrum and plant growth?

[Splash]

My thanks to "2la" for providing the link for the GE 9325K bulbs: http://www.all-glass.com/products/ho...riplites.shtml

I'll try to pull together some useful links on bulbs, spectra, photopic curves, etc. Truthfully, I "rummaged" through hundreds of science, engineering, and industry web sites for about 12-14 hours over the past two days, plus dug through a couple of my own reference books.

(Sheesh! What a nerd! :roll: )

[Daemonfly]

I've had the output graph for a while now. The one thing I wondered is that the red spike seems to be slightly more in the orange range, a bit right of the red levels plants prefer?

[ninoboy]

Can't argue that plants really like the 9325. I use it myself but mix with more other bulbs to neutralize the pink effect.

[2la]

Originally Posted by Daemonfly

I've had the output graph for a while now. The one thing I wondered is that the red spike seems to be slightly more in the orange range, a bit right of the red levels plants prefer?

That's true, but the intensity of that spike is great enough to 'compensate' for the slightly less than ideal emission spectrum. In this case, intensity wins out over spectrum.

[Splash]

Yes, but...

If you multiply the relative intensities of the blue, green and red emission peaks for the 9325K bulb by the relative phtotsynthetic rate from the plant action spectrum, you get a relative "photosyntheic efficiency" around 5:1:3 for B:G:R.

The blue emission band is also broader and all of it closely matches the broad blue "sweet spot" in the photosynthetic action spectrum. I haven't actually integrated the two curves, but by calibrated eyeball, blue definitely wins over red.

Since the emission spectrum is scaled relative to the highest peak (red for the GE bulb, green for most other bulbs), it is unclear to me whether GE actually added more red phosphor or if the red emission peak seems relatively higher because they cut way back on the green phosphor and added more blue phosphor.

As an interesting comparison, the B(440 nm):G(540 nm):R(615 nm) intensity ratio for the 9325K bulb is about 3:3:5. For a typical 6700K bulb, the ratio is about 3:10:7. So you definitely have green decreasing relative to both blue and red, as well as blue increasing relative to red.

Originally Posted by 2la

That's true, but the intensity of that spike is great enough to 'compensate' for the slightly less than ideal emission spectrum. In this case, intensity wins out over spectrum.

[GulfCoastAquarian]

Originally Posted by Splash

The red-emission phosphor is also largely wasted because it peaks at 615 nm, which is also region of low photosynthetic activity. The red "sweet spot" for photosynthesis is way up at 660-680 nm.

Interesting work, Splash. While you're right that the red phosphors don't quite nail the sweet spot, there is still a great deal of output in the 660-680nm range. More so than the typical full spectrum bulb with a more balanced phosphor blend.

It has been wondered if those "wasted" 615nm red wavelengths could possibly be contributors to green water, since their output is strongest at the surface (red wavelengths being attenuated the quickest), but I haven't found any relevant experience to substantiate that claim.

[Splash]

Interesting question. I have seen conflicting information on the web about which wavelengths increase the possibility of algae problems. Some sites or posts say it is too much red light and some say it is too much blue light. Most of the sites and posts were from the marine-reef guys, however, so I'm reluctant to extrapolate their experience to FW planted tanks. (Are they talking brown algae, red algae, or green algae?)

Here is an interesting idea (aka, "wild-a__ed speculation"). The dreaded bba is a red algae. The action spectrum for red algae has a broad peak in the green from about 490 nm to 580 nm. Do our normally very green-weighted lamps predispose us to bba problems?

My personal feeling is that plants and algae have very similar action spectra because they use essentially the same phytopigments. I have action spectra for Ulva taeniata (a broad-"leafed" green macroalgae) and for the green macrophyte Anacharis sp. (Elodea). The spectra look very, very similar, with Ulva having just a slightly wider action peak in the blue.

Unfortunately, most spectra are presented with "relative" scales, so one has to be careful about interpretation. A green algae and a green plant might have very similar relative action spectra, but the algae might require much higher intensity to drive the same amount of growth as the plant. In such a case, providing "too much" light could trigger an algae problem if the increased plant growth can't compensate.

It's a tricky world out there!

Originally Posted by GulfCoastAquarian

It has been wondered if those "wasted" 615nm red wavelengths could possibly be contributors to green water, since their output is strongest at the surface (red wavelengths being attenuated the quickest), but I haven't found any relevant experience to substantiate that claim.

[2la]

We're greatly overstating the loss of efficiency in the action spectrum if we're deeming the 615nm spike a "wasted" emission. Plants have accessory pigments such as phycocyanin that--while somewhat less efficient than chlorophyll A or B in harvesting the energy from light--still allow the leaves to make good use of most of the visible light striking them. That's why I said the substantial magnitude of the spike at 615nm probably more than makes up for the slightly reduced action spectrum at that wavelength. Despite the blue output of the GE "winning" over red, perhaps its the extra 'boost' in the red wavelengths that allows the GE to be so much more effective than most other fluorescent tubes when it comes to growing plants. Certainly the bimodal photosynthetic action spectrum and complex physiology behind photosynthesis and plant metabolism argues against making oversimplistic comparisons of whether the blue part of a light's spectrum is greater or less than the red portion and trying to translate that into how much 'better' plants grow in such light. Likewise, I think one makes too many assumptions when one states that a certain wavelength encourages algal growth. In addition to the possibility that different algal species may respond differently to certain parts of the spectrum, I think lighting spectra are just like any other aspect of maintaining a relatively algae-free tank: It requires balance. Too much intensity in the red or green or yellow or blue or violet portion of the spectrum relative to the rest is more likely to cause an algae outbreak, not the absolute strength or presence of a spike in a particular part of the spectrum. Just boost everything else up again (e.g., other parts of the spectrum, CO2 injection, micros and macros) at relatively the same proportions, and you'll discourage algae growth again by encouraging plant growth. That's my theory, anyway.

[Splash]

Well, I agree with you about this part anyway. The bit about the accessory pigments seems off, however. The action spectrum is based on "whole plant" rather than isolated pigments, so the influence of the accessory pigments is included in the curve.

Originally Posted by 2la

I think lighting spectra are just like any other aspect of maintaining a relatively algae-free tank: It requires balance.

The action spectrum is a direct relationship between photosysnthetic rate of whole-plant pieces to specific wavelengths (more likely, narrow bands) of light, so it is fair to say that increasing pure blue emissions at 445 nm, where relative photosynthetic efficiency is ~80%, will will give more punch than increasing pure red emissions at 615 nm by the same amount, where photosynthetic efficiency is ~30%. The issue that you might be alluding to is whether there is a synergistic effect, where the sum of the combined effect for the blue and red light is more than the effect of each wavelength separately. I don't know of any studies that have looked at that, so I would be speculating to say "yay" or "nay."

However, if you want to take the point a bit further, I will say that plants are adapted to true sunlight and no fluorescent bulb comes close to matching that broad spectrum; the bulbs used for planted tanks all seem to emit in three, relatively narrow phosphor bands. So, at least at that level, plants seem to respond pretty well to narrow wavelength bands. If the synergistic effect of broad bandwidth was a major factor in plant growth, we would all be using mecury-halogen (MH) lighting. However, the fact that commercial hydroponics do use MH lighting might argue that the broad-bandwidth synergy is "non-negligible." I certainly wouldn't recommend growing a plant in pure blue light...although it would be interesting to see the effect!!!

[ninoboy]

I'm not sure whether this is related but I read many articles in the web regarding the blue and red spectrums. They said that too much red and not enough blue will promote vertical growth but the plant will look skinny. Not enough red will stunt the vertical growth. So, the extra red boost that 2la mentioned on 9325 bulb will appear to be more effective just because most of us judge the plant growth by how fast they grow vertically. This is just my amateur opinion :roll:

[Splash]

Interesting. I also need to rethink my comment to 2la regarding the issue of accessory pigments. I seem to recall now (from way back in my distant past!) that accessory pigments can take up light energy at their adapted wavelength, then pass that energy to the cholorphyll/chloroplast complex, which is adapted to and collecting light energy a different wavelength. So by using a very narrow wavelength band, as was done to derive the photosynthetic action spectrum, you could be derailing part of a (synergistic) light-collection system.

I'm sure the botanists have looked at all these issues, so I will keep digging to see what I can find.

Thanks for triggering those long unused neurons, 2la!

Originally Posted by ninoboy

I'm not sure whether this is related but I read many articles in the web regarding the blue and red spectrums. They said that too much red and not enough blue will promote vertical growth but the plant will look skinny. Not enough red will stunt the vertical growth. So, the extra red boost that 2la mentioned on 9325 bulb will appear to be more effective just because most of us judge the plant growth by how fast they grow vertically. This is just my amateur opinion :roll:

[2la]

Well, they should be questioning neurons, not answering ones, since I certainly don't know all the answers! I do, however, sniff out potential oversimplification like a bloodhound, though I'm no less guilty of doing it myself. In any case, what ninoboy is referring to is photomorphogenesis. However, it's the blue spike in the spectrum that does it, not the red, and I've noticed my setups growing more slowly (though "less vertically" may be the better term) than my friend's setup that featured exclusively daylight-type bulbs. However, the leaves in my tanks were usually fuller, and the growth more compact with shorter internodes (i.e., photomorphogenesis). My point in mentioning a potential "boost" offered by the big spike at 615nm was to say that, perhaps, it makes the common misassociation between more compact growth and slower growth less pronounced by speeding up the overall growth.

[Basilisk]

I have conducted a very rudimentary experiment about blues and reds: four sword plants (all same species, and same 'crop'), two in stronger red and two in stronger blue emissions. The result was in fact that growth pattern, compact bushy in reds and tall and thin in blues. It was the leaves' peduncles what really made the difference, not that much in the size of the leaf itself. But a much wider sampling is needed to validate any results.

I figure the growth pattern due to reds and blues may be caused by the red wavelenghts' quicker attenuation as depth increases. Thus, lacking enough red emissions, the plant tries to reach a "redder" spot by increasing its height rather than its span. But as the bulbs won't supply the redder spot sought by the plant going up (in most cases using fluorescents), we don't see a "tree canopy" shape in our plants.

This is just my guess, as it seems a logical assumption, and mayhaps analogical to other plants' growth behavior in somewhat abnormal or non-optimal light conditions.

(Is this getting too off-subject?)