Can A Blacklight Stimulate Growth?

[liveforphysics]

ATJ- Perhaps you could help me with what occurs in this situation.

The lights shut off for the night. I get home 3-4hrs later on work nights. I often click on the black light array ONLY to observe and poke around for a few minutes before I get to bed. No other lights on in the room. The clams, most SPS, most LPS, zoa, etc go from "night mode" into "day mode", and it doesn't take anymore time for everything to open back up than when the main actnics+BLB+10k's come on in the morning.

A good friend with many years of coral study told me that the coral uses its fluorescence to cause the Stokes shift for the purpose of reflecting useable light off the skeleton back through the tissue for the purpose of useful photofeeding.

Back in optic physics in college, I remember doing some labs where we measured the quanity of UV energy per m^2 on the sidewalk in front of the lab on a semi-sunny day. It was a staggering amount of light energy, I think it was around the 7w/m^2 range if my memory is correct. The UV is also able to reach the corals while the sun is lower on the horizion, and become less attenuated by the water it passes through. This makes it the first and last light energy to reach the coral everyday. If the fluorescence enables the coral to take advantage of this early and late light, it could be an advantage in photo-competitive reef situations as we often see in stony coral reefs.

I'm not a biologist, nor do I have any conclusive proof of anything beyond by own observations. I don't have any tools to measure if photofeeding is occuring under the 370-380nm light, but I do have eyes that LOVE to see all the blues fluoresce which are impossible to flouresce with actincs.

I use them for my viewing pleasure. After years of improved viewing pleasure and no signs of problems, I don't think I would ever light a tank without sticking a BLB tube or 2 in the hood.

Just my non-expert, non-scientific $0.02
Best Wishes,
-Luke

[ATJ]

Luke,

First of all, the fact that you can "observe" anything under the blacklight suggests that it also includes visible light as human eyes are not sensitive to UVR. How do you know whether the reaction of the corals, zoanthids and clams are a result of the UVR or the visible light?

Second, assuming it was the UVR from the blacklight that was causing the reaction, how do you know whether the "day mode" is a positive or negative reaction? The observed "day mode" could be the organisms protecting themselves from the UVR rather than obtaining some kind of benefit.

With the exception of some work on deep water corals (which I will cover below) not one of the many papers on fluorescent pigments in corals has suggested that the purpose of the fluorescent pigments in shallow water corals are for enhancing photosynthesis. Most actually suggest the opposite, that the pigments are photoprotective. They use as evidence the fact that a) the fluorescent pigments are found above the zooxanthellae rather than below and b) expression of the fluorescent pigments tend to decrease with increasing depth (i.e. decreasing light).

If the fluorescent pigments were enhancing photosynthesis they would most likely be found under the zooxanthellae where the "reflection" of the shifted light would reach the zooxanthellae. With the pigments being above the zooxanthellae, most of the shifted light will end up in the water (which is also why we see it).

Corals in shallow water are exposed to much more light and UVR than those in deeper water. Corals in shallow water have much less of a need for enhancement of photosynthesis. In fact, many have been shown to actually receive too much light and have various adaptations to either reduce the light they receive or to shut photosynthesis down (photoinhibition) for periods when the light is at its highest. In these cases photoprotection seems a more obvious role than photoenhancment.

The exception to the above is the work done by Schlichter and Fricke (and others) on Leptoseris fragilis from very deep water in the Red Sea. These corals are found at depths between 100 and 160 m where visible light is extremely low. They were found to have fluorescent pigments below the zooxanthellae instead above as in most other corals and it is very likely that the pigments are enhancing photosynthesis under very tough lighting conditions for the coral.

There is no doubt that a lot of UVR reaches the Earth's surface, including the ocean and some of it penetrates the ocean (UVA more so than UVB). Note that less radiation (visible and UV) gets into the water the lower the Sun is because of simple reflection on the water surface. As already mentioned, corals in shallow water already get more than enough visible light so the need to enhance this is does not really exist. Just because something is there (UVR) doesn't mean it is used or needed.

Can you be certain that the blue you are seeing is actually fluorescence not simple reflection of the small amount of violet light emitted with the UVR from the blacklight? What species of coral appear blue? What happens if you place something white under the light? I'm not saying that you don't have blue fluorescence but it is very uncommon. I also know at least one researcher who denies the existence of a fluorescent pigment in corals that emits in the blue although Salih et al. (2000) show a pigment that has an excitation peak of 384 nm and an emission of 486 nm which should appear blue-green.

Finally, while you haven't observed any obvious harm to your organisms from the blacklight (and I wouldn't expect any) how can you be sure that they wouldn't have done better without it? I'm not saying they would have done better or worse with or without the blacklight but merely pointing out you have only only one alternative so it is difficult to make any meaningful conclusions.

[mr.wilson]

Have there been any studies into the possibility that corals fluoresce in order to attract photosensitive zooplankton as a means of "fishing" during night feeding?

[aninjaatemyshoe]

You're mistaking fluorescence from bioluminesence. Fluorescence is a reaction of a fluorescent protein to light within a specific spectrum that results in the emitance of light in a longer wavelength. It only occurs when light hits it; doesn't really occur in to much of a degree at night. Bioluminesence is the emittance of light from a protein that reacts with ATP. This is the light that fireflies and the like emit.

[mr.wilson]

No mistake. I was referring to the fluorescence from twilight and moonlight. I realize Phosfluorescence is a different principal.

[ATJ]

I am not aware of any research into fluorescence being an attractant for prey. It seems an unlikely proposition.

When there is twilight or moonlight and fluorescence is going to be far less significant that the source of the light - the moon and the sky. If the zooplankton where attracted to the light (and many are), they are going to be attracted to the water surface where the light is much brighter.

I have dived many times at dusk and at night under a full moon. The light from the surface dominates and I have not noticed any fluorescence from corals even when wearing a barrier filter*.

Another thing to consider is the lack of fluorescence in azooxanthellate corals. If it was a benefit for prey capture, why don't these corals fluoresce?


* Barrier filters manufactured by NightSea which are used in conjuction with Exciter filters over a light source for detecting fluorescence. The Barrier filters block shorter wave light and the Exciter filters only allow shorter wave light.

[hahnmeister]

There are pigments in corals that experience excitation with UV-A light, and emit visible light...
http://www.advancedaquarist.com/2006/9/aafeature/view

The thing about using UV light is that the bluer you go, the more energy is in the light, so its easier to get photoinhibition with UV light, due to its higher amount of radiation (this is as per a conversation with Dana Riddle).

Most blacklights are of little use to us based more on their actual output than the benefit of their light. There is one exception though... and expensive. OSRAM/Sylvania makes a line of 150watt UV-A induction lamps... about the same efficiency as Power Compact (60 lumens/watt which is actually very good considering its a UV-A bulb and such narrow output). This kind of output would no doubt photoinhibit alot of corals though.

Ill try to find the thread, but its about 3-6 months old and involves dicsussion on the effects/benefits of UV-A in bulbs... the Giesemann Pure Actinic bulbs and halides in particular.

[ATJ]

Originally posted by hahnmeister
There are pigments in corals that experience excitation with UV-A light, and emit visible light...
http://www.advancedaquarist.com/2006/9/aafeature/view

Well, yes, there are, but as already indicated there aren't many such pigments. In the long list provided by Riddle, only 6 pigments are identified as having excitation peaks of less than 400 nm. Of those 6, two of them aren't corals (one is the anemone, Condylactis gigantea and the other is the hydromedusa, Aequoria victoria). Of the four remaining pigments actually found in corals, one is from the deep water Leptoseris fragilis found at depths beyond 60 m in the red sea. So, while you will get some fluorescence with UV light (if you have corals of the species with those pigments) you are going to get far more fluorescence with visible light.

The thing about using UV light is that the bluer you go, the more energy is in the light, so its easier to get photoinhibition with UV light, due to its higher amount of radiation (this is as per a conversation with Dana Riddle).

I'm not sure I agree with this statement. Photosynthesis is a quantum process based on the photons themselves rather than the relative energy levels of the individual photons. It is my understanding that photoinhibition occurs due to the number of photons hitting the photosynthetic apparatus more so than the energy level of the photons. Note that the wavelength/frequency/energy level is important in terms of the action spectra of the pigments but it is the specific wavelengths rather than whether they are longer or shorter.

[pledosophy]

Originally posted by aninjaatemyshoe
I'm kinda getting the feeling that this is the same sorta hogwash like the idea that sleeping next to a clock radio gives you brain cancer.

No really that happenend to a guy a know.

[RiddleLabs]

Aloha Hahnmeister,

UV will cause photoinhibition, but the exact reason (at least in the cases of artificially-produced radiation) is by no means certain.
Sorry for the confusion if I led you believe one way or the other.

Dana

[daytonians]

I still stand by my original opinion that UV should be avoided. It is fine for short periods of time if low intensity. 18 watt bulb on for 1/2 hour a night is probably not going to hurt anyone. I would not run black lights all the time, or install powerful bulbs.

Also, the assertion that the farther away you get the weaker the light is, is just wrong. You are confusing optics with the spread of light coming off a bulb. Check this with a camera. Hold it right next to the tank, aimed at the center of your display. Then back off a few feet. The reading will remain the same.

[MCsaxmaster]

Originally posted by daytonians
I still stand by my original opinion that UV should be avoided. It is fine for short periods of time if low intensity. 18 watt bulb on for 1/2 hour a night is probably not going to hurt anyone. I would not run black lights all the time, or install powerful bulbs.

Also, the assertion that the farther away you get the weaker the light is, is just wrong. You are confusing optics with the spread of light coming off a bulb. Check this with a camera. Hold it right next to the tank, aimed at the center of your display. Then back off a few feet. The reading will remain the same.

But intensity really is very important. There's more UV at 20 m depth in the ocean than there is a foot or so from a blacklight. Yes, they produce UV light, but very, very little as compared to the sun.

Also, the intensity of light (including UV) does decrease the further you are from the bulb. This decrease is inversely proportional to the square of the distance.

Chris

[daytonians]

Chris,

Wrong. The intensity of the light never decreases, it just gets more spread out, which will register lower readings on a light meter the farther away from the bulb you get. That is why we can see stars that are billions of miles away. When photographing the moon, you use the exact same camera settings that you would for photographing outside on a sunny day here on Earth.

We are discussing what your eye sees though. That is totally different. Your eyes are like camera lenses. Not a zoom lens, but a standard lens. It has a fixed angle of view.

Take a solid white wall that is evenly lit. (Try to stay with me here) As you back away from it, the light is spread out, but your eye sees more and more of the wall. Standing 3" from a wall, you can only see about a 6" circle. Back off to 6" and you can see like a 12" circle.

So, the decrease of intensity is exactly matched by the increase in field of view. Light seen stays the same.

[ATJ]

Light is made up of photons. Each photon has a single wavelength. The wavelengths of photons in visible light range from 400 to 700 nm. A photon of one wavelength is identical to every other photon of the same wavelength regardless of how the photons were produced whether it be from a star (including our Sun), an artificial light source or bioluminescence. They have the same energy level, which is dependent on the wavelength. They travel at the same speed, which is also dependent on the wavelength but also on the optical density of the medium through which they pass.

The intensity of light is defined as the amount of light striking a certain area over time. The only two factors that affect intensity are the number of photons striking the specific area over time and the energy level of those photons. When using quantum units, such as Einsteins, only the number of photons is relevant. When energy units are used, such as watts or joules, the number of photons is the dominant factor with wavelength having a much smaller influence.

The number of photons reaching a surface will be influenced by the amount of light (total number of photons) emitted from a light source, the area over which those photons are spread and any attenuation by the medium through which the light passes. Many of the stars we can see from Earth are much larger than our Sun and put out, but our Sun is much closer and so proportionally more of our Sun's photons reach the Earth than those from other stars. Even with our Sun, only a small proportion of the photons reach the Earth with the others heading off in other directions. And, yes, it is to do with the spreading out of the light, but it still affects the intensity. The Earth is closest to the Sun every January and more of the Sun's photon's reach the Earth.

Attenuation of light occurs with the Earth's atmosphere as photons are absorbed, reflected or refracted by the air and particles in the air. The shorter the distance of atmosphere the light passes through, few photons that are lost. This is why the intensity is greatest when the Sun appears directly above the Earth and it decreases when the Sun appears just above the horizon.

Attenuation of light also occurs with water and at a much greater rate than in air. The light intensity can be reduced to 50% in around 5 m of clear water.

The inverse square rule "decrease is inversely proportional to the square of the distance" only applies to point light sources. The light intensity DOES decrease as there are fewer photons reaching the area and it IS because the light is spread out over a greater area. When you double the distance, the light is spread over four times the area and so the intensity is reduced to one quarter. Triple the distance, the area of spread is 9 times and the intensity is one ninth. Note that the Sun and the stars are all point light sources.

A fluorescent tube is not a point light source, at least not at the distances we use them over. While light intensity does decrease with distance, it does not decrease as quickly as with a point light source. This is because the tube is effectively a row of point light sources. If you take each point individually, you will get the inverse square rule but the light from each point overlaps with the next point and so the "spread" includes the other light. The further you go from the tube, the more light you pick up from other points along the tube.

[Sparkss]

Originally posted by MCsaxmaster
UV-A (aka long-wave UV) ranges from 400 - 320 nm, UV-B from 320 - 280 nm and UV-C from 280 - 200 nm. Technically all of this is 'near UV' with 'far UV' ranging from 200 - 1 nm. As such, what I should have said and what I meant is that blacklights produce UV mostly near the visible spectrum, that is, mostly UV-A which is not particularly dangerous. They produce very little UV-B (damaging) and essentially no UV-C (DEADLY). UV-A is long wavelength UV light, not short...

Originally posted by hahnmeister
Ill try to find the thread, but its about 3-6 months old and involves dicsussion on the effects/benefits of UV-A in bulbs... the Giesemann Pure Actinic bulbs and halides in particular.

I came upon this thread while researching building an LED array to supplement the halides, similar to using actinic VHOs. Most of the LEDs that seemed to be what I was looking for were labelled as "UV" and carried the warnings about not looking directly at them. I know that most actinics are between 420nm and 450nm (maybe as high as 470nm for some).

So here is my question, based on some of the information posted here : So long as the wavelenth of the LED is above 400 it should be safe to put over our tank ?

Aren't actinics somewhat UV ? URI stands for Ultraviolet Research Institute IIRC, and they are considered the leader for VHO actinics.

I am just trying to make sure that I understand what is what so that when I finally do source out the LEDs I get the right ones (or at least don't get the wrong ones).

Do I need to pay more attention to the wavelength than whether they label it UV or not ?

I know this is a little off topic for what the thread was originally started for, but it dovetails right into the majority of the information in the other posts. Thanks