What's the difference between Halogen, Metal halide, LED and incandescent

[brooke.belanger]

I was curious as to what the main differences are between Halogen, Metal halides, LED and incandescent lights affect reef tanks and how they affect corals and help them to grow. I'm considering getting corals and would like to understand how the lights work.

Also anything about the lumens or kelvin of light intensity information would be helpful. I have a vague idea, but I don't really understand all of it.

[gaberosenfield]

The difference between the kinds of lights is the mechanism by which they generate photons (light "particles"). No serious reefers use halogens or incandescents because they consume huge amounts of electricity and produce huge amounts of heat per photon. You would go bankrupt and boil your tank if you tried using incandescent lights to grow corals!

The three main types of lights people use to grow corals are T5 fluorescents, metal halides, and LEDs.

T5s are the cheapest to set up initially and have many options for bulb colors and combinations. But they require frequent bulb changes and many bulbs for a decent sized tank. T5s produce light by pumping an electric arc (think like a big spark) through a glass tube that has all the air sucked out (vacuum tube) and a tiny bit of mercury inside. The electricity excites the mercury atoms inside the tube and causes them to release high energy photons (in the UV spectrum). These photons hit a phosphor coating on the inside of the tube (the white or colored part of a fluorescent tube; the glass itself is clear), which causes the atoms of the phosphor to become excited. The phosphor coat then releases lower energy visible light which we (and corals) can see (and use to grow). T5s are also the least efficient in terms of electricity usage per photon produced.

Metal halides cost a bit more to set up but produce much more light. Even really big tanks only need a few of them to grow corals. The bulbs still need to be replaced every once in a while but not as often as T5s. There are also quite a few color options available. Metal halides produce light in a similar way to T5s. The difference is that, instead of a phosphor coating, the mercury is mixed in an inert environment (under argon gas) at high pressure with compounds called metal halides (e.g. sodium iodide or indium bromide). An electric arc excites the mercury and vaporizes all the components in the bulb. This excites the atoms of mercury and metal halides, causing them to release photons. The UV photons are filtered out by UV filters in the bulb (and often an extra one is placed outside of the bulb in the fixture). The biggest downside to halides is how hot they get. They produce more light per unit electricity than T5s, but they produce so much more light that they still get VERY hot. You will definitely need active cooling system (e.g. fans) to keep them cool, especially if you put them in a canopy.

LEDs cost the most to initially set up by far. But they produce the least heat, very rarely need replacing (only once a decade if they are really taken care of), can be controllable (e.g. you can dim them, or even dim some colors and not others to change your color spectrum), take up the least space, and are by far the most efficient in terms of photons per unit electricity. LEDs produce light by pushing electrons across a junction between two different kinds of semiconductors. As electrons move from the higher energy semiconductor to the lower one, they must release energy. To do so, they release photons, which are focused by the LED to make the light we perceive. Many LED systems still require active cooling systems, but some do not. The downside, other than initial price, is that LEDs are the newest of these lighting technologies and some reefers aren't convinced they grow corals as well as the older "tried and true" methods. However, many people are using them and growing corals just fine, so I tend to think that LEDs are very capable of growing corals.

Definitions

Lumen: a unit of measurement for visible light. Note that this is not the intensity of light, but rather the "amount" of light. Thus, a 1000 lumen light concentrated into one square meter might seem quite bright, but spread out that light over 10 square meters and it will seem very dim. More lumens in the same area means a brighter light.

Color temperature: the temperature required of a theoretical perfect black body radiator to produce the color spectrum of a given light. In layman's terms, you know how a piece of iron turns red when you heat it up enough? If you keep heating it, it turns white. And if you keep heating it some more (in an oxygen free environment so it doesn't turn into rust), it turns bluish. Theoretically, you can keep heating up the iron until it produces any wavelength of light (in reality the atoms would break down at some point, but that's why I said a "theoretical perfect black body radiator"). At any given temperature, the hot iron will produce a certain amount of light of a certain set of wavelengths (e.g. colors). For example, if the iron were a perfect black body radiator, at 6500 degrees kelvin (a temperature unit equal to celsius temperature minus 273 degrees) the iron would produce a light spectrum identical to that of sunlight on a clear day at sea level on earth. At 12000 degrees kelvin, the iron would produce a spectrum similar to sunlight on a clear day under 10 meters of water. The hotter the iron gets, the more blue-shifted the spectrum gets. Hence, the 20000 kelvin lights look very blue.

[brooke.belanger]

Wow. Thank you so much for the detailed response; that answered all of my questions!

[gaberosenfield]

No problem! I'm glad to help. May I ask what size tank you're running? It seems like most people with small tanks run LEDs. A lot of people with small to medium tanks use LEDs or T5s. And most people with large tanks tend to run metal halides. I'm not sure it really matters too much, as all can grow corals, but there are differences in terms of the amounts of light they can produce and sizes they come in. For example, it wouldn't make much sense to run a 15 gallon tank off of a metal halide. Even the small metal halides would have to mounted many feet above the tank to keep from bleaching every coral in there!

[mbingha]

Originally Posted by gaberosenfield

The difference between the kinds of lights is the mechanism by which they generate photons (light "particles"). No serious reefers use halogens or incandescents because they consume huge amounts of electricity and produce huge amounts of heat per photon. You would go bankrupt and boil your tank if you tried using incandescent lights to grow corals!

The three main types of lights people use to grow corals are T5 fluorescents, metal halides, and LEDs.

T5s are the cheapest to set up initially and have many options for bulb colors and combinations. But they require frequent bulb changes and many bulbs for a decent sized tank. T5s produce light by pumping an electric arc (think like a big spark) through a glass tube that has all the air sucked out (vacuum tube) and a tiny bit of mercury inside. The electricity excites the mercury atoms inside the tube and causes them to release high energy photons (in the UV spectrum). These photons hit a phosphor coating on the inside of the tube (the white or colored part of a fluorescent tube; the glass itself is clear), which causes the atoms of the phosphor to become excited. The phosphor coat then releases lower energy visible light which we (and corals) can see (and use to grow). T5s are also the least efficient in terms of electricity usage per photon produced.

Metal halides cost a bit more to set up but produce much more light. Even really big tanks only need a few of them to grow corals. The bulbs still need to be replaced every once in a while but not as often as T5s. There are also quite a few color options available. Metal halides produce light in a similar way to T5s. The difference is that, instead of a phosphor coating, the mercury is mixed in an inert environment (under argon gas) at high pressure with compounds called metal halides (e.g. sodium iodide or indium bromide). An electric arc excites the mercury and vaporizes all the components in the bulb. This excites the atoms of mercury and metal halides, causing them to release photons. The UV photons are filtered out by UV filters in the bulb (and often an extra one is placed outside of the bulb in the fixture). The biggest downside to halides is how hot they get. They produce more light per unit electricity than T5s, but they produce so much more light that they still get VERY hot. You will definitely need active cooling system (e.g. fans) to keep them cool, especially if you put them in a canopy.

LEDs cost the most to initially set up by far. But they produce the least heat, very rarely need replacing (only once a decade if they are really taken care of), can be controllable (e.g. you can dim them, or even dim some colors and not others to change your color spectrum), take up the least space, and are by far the most efficient in terms of photons per unit electricity. LEDs produce light by pushing electrons across a junction between two different kinds of semiconductors. As electrons move from the higher energy semiconductor to the lower one, they must release energy. To do so, they release photons, which are focused by the LED to make the light we perceive. Many LED systems still require active cooling systems, but some do not. The downside, other than initial price, is that LEDs are the newest of these lighting technologies and some reefers aren't convinced they grow corals as well as the older "tried and true" methods. However, many people are using them and growing corals just fine, so I tend to think that LEDs are very capable of growing corals.

Definitions

Lumen: a unit of measurement for visible light. Note that this is not the intensity of light, but rather the "amount" of light. Thus, a 1000 lumen light concentrated into one square meter might seem quite bright, but spread out that light over 10 square meters and it will seem very dim. More lumens in the same area means a brighter light.

Color temperature: the temperature required of a theoretical perfect black body radiator to produce the color spectrum of a given light. In layman's terms, you know how a piece of iron turns red when you heat it up enough? If you keep heating it, it turns white. And if you keep heating it some more (in an oxygen free environment so it doesn't turn into rust), it turns bluish. Theoretically, you can keep heating up the iron until it produces any wavelength of light (in reality the atoms would break down at some point, but that's why I said a "theoretical perfect black body radiator"). At any given temperature, the hot iron will produce a certain amount of light of a certain set of wavelengths (e.g. colors). For example, if the iron were a perfect black body radiator, at 6500 degrees kelvin (a temperature unit equal to celsius temperature minus 273 degrees) the iron would produce a light spectrum identical to that of sunlight on a clear day at sea level on earth. At 12000 degrees kelvin, the iron would produce a spectrum similar to sunlight on a clear day under 10 meters of water. The hotter the iron gets, the more blue-shifted the spectrum gets. Hence, the 20000 kelvin lights look very blue.

I already knew most of what you posted, but what an incredibly well thought out post. this kind of information sharing is why I love this site! I did not know about the Kelvin rating of lights, so I learned something new, thanks :thumbup:

[brooke.belanger]

I have a 40g FOWLR tank at the moment; it's more tall than it is long
I'll just give you a little more info too:
2 clowns
1 firefish
1 yellow tail damsel
1 coral beauty
Crushed coral for the base
And currently just small crappy LED lights that came with the tank good when I bought it
Already have a protein skimmer
And a koralia 750 powerhead

[gaberosenfield]

@mbingha: I'm glad you enjoyed my post! I totally agree with you about this site. There are tons of very smart, well read, and experienced people here who are very willing to share information. And BTW, I am not an expert on optics or anything, I just read a lot and took a lot of chemistry and physics courses in college. So if an actual expert on optics reads my post and finds something that isn't quite right, PLEASE correct me! I think this site would be even better if everyone wanted to be corrected

Back to you, brooke.belanger: At that size, you could go with any of the above three lighting options. I probably wouldn't go with metal halide if I were you, but that is just my opinion and I have seen awesome looking 40s and even 30s with metal halides. I am partial to LEDs because I like technology and low maintenance and LEDs give you both They are also cheaper in the long run because you don't need to replace the bulbs, but it will take years for the initial cost + running cost to equal out. There are tons of proponents of T5s, so the choice is yours. If you do chose to go the route of LEDs, I would stay away from the DIY stuff. I did that on my last nano (20 gallon DT). It worked very well as far as growing corals, but the time and stress it took me to build it all was not worth the 30% I saved off buying a pre-made light that would've looked a lot better too. Also be sure to get a dimmable LED fixture if you go that route, because they are typically capable of being far brighter than your corals need/want them to be!

[brooke.belanger]

Yeah I'm definitely a little too lazy to try and do the setup myself! From a the reading I've done and the input you gave me, I believe the T5 is the way I'll go. Thank you so much for all that information! I'm actually learning about all that black body radiation is school as well haha, so everything you said made a ton of sense. Thanks again!

[gaberosenfield]

Ahh reefing! It suddenly makes physics, chemistry, and biology so much more relevant to our lives

[mbingha]

Originally Posted by gaberosenfield

Ahh reefing! It suddenly makes physics, chemistry, and biology so much more relevant to our lives

Haha yes it does. I'm going to be building my leds along with an arduino controller (jarduino) and I wish I had taken a circuits class as an elective back in college. Of course at the time I would have never considered adding to my course load, engineering was hard enough as is lol.

[brooke.belanger]

I enjoy how science students are the ones to mostly get reefs and aquariums!