Lumens or kelvins?

[dshin1]

can someone please clear up what to look for when purchasing lights? is the lumens or kelvins more important. also at what lumens is the light optimal for coral?

[Phurst]

The color spectrum of the light si primarily what you're going to be concerned with.Spctrum is commonly measured as degrees Kelvin. Generaly speaking, the higher the color temperature, the bluer the light is. 6500K is pretty yellow light. 10,000K is brigt white, and 20,000K is pretty blue. Generaly speaking, reef lighting will fall between 10,000K and 20,000K. The exact color temperature is largely personal preference, with lighting clsser to 10,000K giving better growth, and 20,000K better coloration.

Lumens are a measure of percieved light intensity, and will vary depending on bulb type and wattage. Typicaly reefers are concerned only with color temperature and bulb wattage, although the efficiencies of a given bulb type and it's reflectors does come into play as well.

If you want to talk intensity, typicaly PAR (photosyntheticaly available radiation)and PUR (photosyntheticaly USABLE radiation) are the figures we would be concerned with, and can be determined uing a PA meter, although PAR values can be estimaed based ton the bulb type, wattage, manufacturer, ballast type and reflector type.

Was there something specific you were wondering about?

[dshin1]

thank you reef monkey. that clears up a lot. so what your saying is the most important aspect is the spectrum? get 10000k for best growth. what about the wavelength? LFS is telling me i need to keep my lights at a range of 420-480. is that the same as 10000k? i just looked at some threads and some are using LEDs. can LEDs reach 10000k-20000k? sorry for the questions, just trying to learn.

[Phurst]

Yep, LEDs can easily hit the 10-20k range and even higher.

Spectrum and Kelvin are closely related. Light in the 420nm (nano meter) range is what's called "actinic" lighting. Those are the very blue, to almost purple lights you se on many reef tanks. Light in those wavelengths tends to bring out the natural flouresence of many corals. While actinic light is not strictly necessary, many people prefer to use primary lighting in the 10,000K range to get good growth, and use actinic lighting to offset the yellowish cast bulbs in that range can produce.

You surely don't want all of your lighting in the actinic range. While corals will use some light in that range for photosynthesis, it's mosty for our own personal aesthetics.

For example, my main lighting is 2 400 watt metal halide lamps with 10,000k bulbs, and 2 54 watt T5 flourescent tubes that are actinic because I find the overall effect pleasing. I could certainly go without the actinic lights and the coral wouldn't care a bit.

What kind of lighting are you considering? Flourescent, LED, metal halides? What sixe tank are you looking to light and what would you like to keep in it?

BTW, Reef Monkey is just my title around here
I go by Phurst

[dshin1]

sorry phurst. and thanks again for all the info. i have 2 vho 220 watt lights and 4 60 watt all 46.5 inches. i have some coral and clams and they seem to be doing fine but there seems to be a lot of algae growth all of a sudden. i haven't changed anything, feeding is the same, cleaning is the same, nothing new has been added. my friend suggested i need new lights. i wanted to find out more for myself and ask some questions. and i think the vho are 10000k the other ones i can't remember.

[Phurst]

LOL, no need to appoligise.

As bulbs age, the spectrum of light they emit tends to shift more towards yellow. Algae tend to prefer more yellow light, even down into the 5,000K range. That's one way we know it's getting time to change our bulbs. How long have you been using the bulbs you currently have. Flourescent bulbs are reccomended for replacement anywhere between 6 months and a year. IMO a year is really pushing it. I replaced my PC bulbs every 6 to 8 months.

[dshin1]

i guess around a year. i'll get new bulbs as soon as i can. i hate cleaning alge. the less the better.