Is there such a thing as too much light?

[jason the filter freak]

I don't know wether or not this is a stupid quesition but, I'm working on building my own hood for a 5 gallon nano tank....

 

In the hood I've made there are 125 LEDS being fed by of course a massive 12 volt DC power supply.

 

90 are white LEDS

35 are blue LEDS

 

I hooked it up in a room roughly 25 by 20 feet with the lights off, and it was like an air plane was comming in for a landing!!

 

It lit up the entire room like day light, the olny reason i did so many is because my calculations showed that 125 LEDS = 10 watts (roughly)

 

Yea I know i coulda saved money and gone with a florescent fixture, but the LEDS were brighter (maybe a mistake?, and last longer)

 

Is it the intensity of light, or the amount of light that corals need? I also don't want to blind the , I'll be putting in the tank.

[davelin315]

It has to do with PAR (photosynthetic active radiation or something like that). That's the light that is usable by the zooxanthellae of the coral. The LEDs you have may or may not have good PAR despite how bright the tank may be. If you have poor PAR readings you may end up with a bad nuisance algae problem which will thrive in poor lighting conditions. Brightness, or lumens/lux, does not have anything to do with how good your lighting is as far as I know. There's a PAR meter that is currently in VA, you may want to grab it before it makes its way to MD and get a readout on your light set up.

[dhoch]

I've got my own personal one and would like to get a PAR reading on that bad guy....

 

Dave

[mogurnda]

The short answer is yes, you can have too much light. If the corals are overilluminated, you end up with photoinhibition and poor coral growth. I'd love to know what kind of PAR reading you get with that setup.

 

It's very exciting to see someone local get a LED setup. After this review by Dana Riddle, I am convinced that LED setups are more than a kiss and a promise. Also, Dana gives some ideas about how to compare PAR between halides and LEDs, and what some of the problems are.

[jason the filter freak]

I showed the led fixture to some one else, and they decided to buy if for $60 and put a screen in front of it and use it as "mood" lighting for his rec room, good riddance, it ony cost me $20 minus the resistor and wiring work done by hand. I've read more about the led fixtures, and it looks like you need to buy the ones meant for marine use any way.

 

I'll go with a PC light foxture

[mogurnda]

Missed the part about it being DIY. Always a bad idea to post before completely waking up.

[fab]

Jason,

A bit of basic physics of light for you. You asked if the amount of light or its intensity was more important. The answer is 'it depends.'

 

First, what do you mean by the amount of light? I will substitute brightness for amount? So what is brightness? Brightness, to an extreme, is that attribute of light that actually hurts to look at. At the other extreme, as brightness diminishes more and more, the light looks dimmer and dimmer until it just disappears. Brightness is actually intensity, but with a qualifier. I'll try to explain that.

 

Light that you normally see is made up of many colors. When we say it is made up of many colors we mean that those colors are present in what we see. We see the blend of the colors, not the individual colors; unless the light we are looking at is specifically a single color.

 

Think about sound. If you hit a single note on a perfectly tuned piano, you will hear a single note. in physics we would say you hear a sound at a single frequency that corresponds to that note. We could just as well say the sound is at a single wavelength. Now play several notes at the same time, a chord. Now you don't hear each of the several notes; instead you hear a blend of the notes, the sound of the whole chord. Think of a single color of light as being a single note, sounding out by itself. Think of the color white, which has all colors mixed together as being the sound of all 88 piano keys being hit at once. Not a pretty sound but a decent analogy.

 

Now, if you hit the 88 keys gently and can barely hear the sound produced, that would be a low intensity sound. If you hit them stongly and the sound comes out very loud that would be a high intensity sound. Light follows this analogy, we just don't say soft and loud light, we say dim and bright light to mean the same thing as low and high intensity light. So where is the qualifier I said I'd explain?

 

Here it comes. This will take a bit, so bear with me. Suppose you hit all 88 keys at the same time, but instead of hitting them all with equal force you just barely hit some of the bass notes on the left of the piano and you hit some of the high notes really hard. Now the sound would be different. In fact a musician would say it has a different 'color' from when you hit all keys equally hard. [Now a short aside:]The bass notes have long wavelengths or you could say they are at lower frequencies than the high notes. On the other hand the high notes, high frequency, have shorter wavelengths than the bass notes. In sound physics people use frequency and wavelength interchangeably to convey the same information. In light physics, people generally don't refer to a color by its frequency; rather they refer to it by its wavelength. Reds are longer wavelengths than blues. [ end the short aside] So back to the sound and light analogy. When you hit the longer wavelength keys softly and the shorter wavelength keys very hard, it would be like having a light that has high intensity in its blue components and low intensity in its red components. The light would be more blue looking than red. In fact it might look a bit blue overall. The reds are still there in the light, they just aren't intense. They just aren't as bright as the blue components.

 

In the aquarium hobby, you will hear about the spectrum of lights. That is like the 88 key sound. When the musician said that the 'color' of the sound was different in the example above, he was actually saying the spectrum had more enery in the high notes than in the low notes. When you look at a spectrum chart for an aquarium light you will see all the colors represented on the chart. The height of the graph at each color indicates how intense that color is in the final blend of all the lights. If you see a spectrum chart with a peak in the blue area and low levels in the red area that would be a light that corresponds to our 88 key sound example with low intensity bass and very intense high notes. The shape of that chart is what we mean when we refer to the spectrum of a particular light. When we use the term 'the spectrum' of the light we are using shorthand for 'the power spectrum' of the light. The power spectrum of a light is the set of intensity values for each color that contributes to making up that light. It's the same as the set of strengths with which you hit each of the 88 keys. You might hit each key with a strength peculiar to that key. The list of those strengths, key-by-key, would be the spectrum of the sound you would produce.

 

Now, why are brightness and intensity not the same? They are in the most general sense of the words. But, not in a strict sense. Brightness speaks to what you see with your eyes, how it affects you. Intensity refers to how much energy there is. Not all colors of light are visible, just like humans can't hear all sounds. Blue light has short wavelengths. If you make the wavelengths shorter and shorter you will make ultra-violet light and the light will disappear from your vision. You can't see UV light. Now that you are producing UV light, invisible though it may be, you can turn up the intensity of the light all you want to and it will remain invisible. Now go the other way. Back down on the wavelengths and get back to the first light that you can see. It will be a violet. It will actually appear to be fairly dim, regardless of how high you crank up the intensity. Our eyes don't respond as well to violet light as they do to colors with lower wavelengths like greens and yellows and reds. What do I mean by not respond well? Put a lot of energy in and it doesn't appear much brighter. So intensity and brightness aren't the same when you are dealing with light near or beyond the ends of our visible spectrum. The same thing happens for the long wavelengths, below red or infrared. We can't see infrared. BTW, snakes can, but that's a different story!

 

So your question was not stupid. Generally, questions are never stupid in the first place. There are stupid answers, but not stupid questions. Not knowing something yet is not being stupid. It is just being uninformed... so far. Not wanting to be better informed might be stupid in many cases. With respect to your specific question, most people in the hobby know less about light, color, sound, spectrum than what I have just informed you.

 

fab

[davelin315]

Sounds like someone remembered their 5th grade science! I'm still on summer vacation so I might be mistating something, but here goes!

 

Shorter explanation, shorter the wavelength of the light in general the more intense it is (basically, a longer wavelength is less frequent while a shorter wavelength is more frequent). The longest wavelengths are radio waves which are in fact part of the electromagnetic spectrum. The shortest wavelength is gamma rays. If you were hit by radio waves, no big deal. If you were hit by gamma rays, see ya later!

 

Like fab said, we can only see certain parts of the spectrum. What we see is the colors of the rainbow (ROY G BIV, remember that?). Red, orange, yellow, green, blue, indigo, violet. The longest wavelength is always red which is why it appears at the outside of rainbows. The shortest is violet, which is why it's always on the inside. Violet is much more "intense" than red light, but the strength of the light is also dictated by... can't remember the term... distance from the "at rest". Think of a sine wave, it goes up and down. The higher the wave goes, the more powerful it is. Compare it to standing at the beach. The higher the wave, the more likely it is to knock you down. The more frequent the waves, the more you will get knocked down.

 

Don't know if I cleared anything up, but the light we can see is "weak". It may hurt to look at an intensely bright light, but it won't do a whole lot of damage unless it's carrying a lot of very powerful waves in it, such as UV. Ultraviolet light is what can get you. That's why you get a sunburn in the sun or even on shady days. The UV light is there whether you can "see" it or not. That's why you can do permanent damage to your eyes if you look at the setting sun. Even though the sun appears to be dim, the UV rays are still there and if you stare at it head on, boom, your eyes suffer. It's also like a UV sterilizer. We can see the glow of the light, but it's certainly not overpowering like a metal halide light. However, if you shine it on yourself, you'll burn your skin (and eyes) very quickly with UV lights before anything will happen with the MH.

 

Bet you wish you remembered your 5th grade light unit (I'm wishing the same thing right now since I have to teach it in about 2 weeks)!

[jason the filter freak]

I know the RGB spectrum, I'm not completely daft.

 

 

I mean to ask could the brightness actually cause harm to the fish, i.e. blind them everytime the lights come on.

 

I know the RGB spectrum, I'm not completely daft.

 

I slept though chem, not biology :wink: I passed my spectrometer test in 101 thank you. What I'm having trouble comprehending here is the units they use for LEDS, I'm not sure what they mean, I have a rough grasp of the spectrum in terms of 10K 20 K 15K etc. How ever in theory could this be duplicated with the application of LEDS?

 

My main question is what is 25,000MCD, 60,000 MCD, 15,000mcd etc what is MCD is it similar to or a sort of specrtum measurement? Or is it a measure of brightness like lumens, foot candle, candlepower (yes i relize those are diffrent types of measure)

 

So is it possible to get the correct amount of intensity out of leds to be as good as a MH buld, if you spend the time to make your own? Anyone care to shed some on the situation?

Edited August 27, 2006 by jason the filter freak

[dhoch]

I belive (but not 100% sure) that MCD is a measure of brightness.

 

As for creating one of these on your own to match MH you would want to do some spectral research. Actually the article linked above does some of that for you. Try to recreate the intensities and spectrum of a MH (or other type of bulb) with the LEDs.

 

You would probably have to get multiple types of LEDs.

 

Dave

[davelin315]

Hey Jason, no offense meant by the explanations. The "brightness" you see doesn't affect the amount of light a coral gets that is useful. A super bright fish tank might cause a fish to hide all day and heat up the water because of absorbed light energy, but it's not necessarily going to cause it to be too much "harmful" light.

 

Check out Sanjay's threads on RC. He does a lot of studies on lighting and how much PAR it puts out. The LEDs may or may not put out the same PAR, but if they are run of the mill ones chances are they won't put out a lot of UV light which is what corals need. An example of this is a halogen bulb. It may put out a ton of "brightness" but you couldn't put it over a reef and hope for the same results as a duller metal halide bulb in terms of "brightness".

 

The only thing that LEDs that are strictly for coloration would do (as far as the temperature rating in Kelvin) is make it appear more pleasing to the eye. Kind of like taking a soft white bulb versus a daylight bulb for a regular incandescent lamp. You may like the yellowish color or you may like the blue color, but all that is is a measure of what light is being reflected back to you because of the output. Corals will thrive under the proper lighting, we add different color spectrums so that we can see the colors that we want to see in them.

[fab]

MCD is a particular intensity measurement used for LEDs. It measures 'boresight' energy under specific measurement protocols (setup and procedures) and can be used to compare LEDs to each other. It is not that useful for an aquarist, particularly in comparing LEDs to non-LED lights.

 

Here is some background detail...

Imagine two light sources that emit light. One emits all of its light in a single direction, in an extremely tight beam. This first lamp is an LED. The other emits its light in all directions, light a conventional light bulb. Now imagine a test setup that places a small light intensity meter right in the narrow beam of the first light. Turn the light on with a specific amount of electrical current. The specific amount can be found in measurement manuals. Take a measurement and you will measure pretty much the total light output of that light. This is how MCD is measured for LED lamps. Now substitute the conventional light bulb in the measurement setup. Only a small fraction of its light will impinge on the intensity meter.

 

If you were given the two readings you would not be able to tell which light produced the most total light power; unless the LED reading was lower than the light bulb reading. More importantly, as an aquarist, you would have almost no useful information. The MCD measurements for LEDs is an on-axis measurement. It only represents the amount of light power emitted in what is called the boresight direction and for a specific amount of electrical driving current. LEDs were not originally very useful for area lighting devices. They were useful for pointing light in a specific, single direction. They produced very narrow light beams, e.g., 1-2 degrees. Now LEDs are available with wider beamwidths, e.g., 45- 90 degrees.

 

If you want to compare LEDs to other candidates for aquarium lighting, you must compare spectral composition, which you indicate you know all about. Look a the power spectral density charts and at total power output. Don't confuse light power output with power consumption.

 

One other note. Light energy is light energy. It doesn't matter whether it comes as a reflection off your girl friends eye or from a metal halide lamp. Light energy has a spectral composition that is measured by its power spectrum density. That is a measurement of the amount of energy at each wavelength of light that is emitted or reflected. If you want to compare lights you need to know the PAR produced by the lamp, which is the total phtosynthetically active radiation and its spectral power density. If you are doing this for an aquarium application, you need to also know the PUR rating of the lamp, which rates the 'useable' portion of the 'active' radiation. What is useable? It is that portion of the spectrum that the consumers of light in your aquarium actually consume.

 

Unfortunately, this information is expensive to develop for lamps and isn't readily available to consumers just for the asking. So you are stuck with word of mouth comparisons which are notoriously inaccurate, with reading lots of test reports where you have to worry about who paid or who may have influenced the author, or with conducting your own experiments.

 

fab

 

......................................................................................

 

Jason,

BTW the short answer to your original questions is a definite YES. YES, you can have too much light! Just as you can suffer from too much light, so can any other living organism. You can burn things with too much light, such as the retina of a fish's eye. If the light energy is in certain parts of the light spectrum you can kill tissue. This becomes particularly severe if the light intensity is high.

 

You must stay within the right range of light intensity at each color component of the light. That means there is a low intensity you want to stay above so the light component can do its good and there is a high intensity you need to stay below so you don't burn things up. At some color components, you may want to get down to ZERO intensity; e.g., at UV-b wavelengths.

 

How much light can your own skin handle?

 

fab