kelvin vs. wattage

[kenny2064]

so i know that typically you want about 2+ watts per gallon for lighting my question is this would a 70 watt k2 viper be enough for a biocube 29 with a 14k bulb or would I have to substitute the bulb for a 20k bulb to compensate the low wattage...I think i understand the rule of thumb where kelvin is the spectrum of light where the wattage is the power while both are important would a 70 watt k2 viper be enough for a bc 29...i dont have sps at all have mixed zoas, blasto, shroom, a sunflower (i think) but let me know

 

[Chris Jury]

As you say, the color temperature is reported in Kelvins. In practice, most everything above 10K or so doesn't correspond remotely to any blackbody spectrum, and therefore 12,13, 14, 15, 20, 50K, etc. bulbs are laballed as whatever the manufacturer decides to label them as In general, the higher the Kelvin rating, the bluer the light looks to most people, but again, it's totally arbitrary depending on what the manufacturer decides to call the bulb. For instance, a 14K bulb of one brand may look as blue or bluer to you than a 20K bulb. A 14K of another brand may look much whiter to you. I'd try to see any bulb in person to get an idea of what it looks like, if possible. Different bulbs WILL vary in their brightness (intensity) though, and this often has nothing to do with color temperature rating for bulbs in this range. For instance, bulb 14K bulb from manufacturer A may be dimmer than 20K bulb from manufacturer B. However, 14K bulb from manufacturer C may be a lot brighter than either of the others. I'm not sure how many 70 watt bulbs Sanjay has had a chance to test yet, but his lighting guide here is a great resource for bulb decisions.

For that size tank with the animals you have, I think a 70 watt bulb of pretty much any sort should work very well. There's no inherent advantage of a 20K over a 14K or vice versa. Oh, and as for the watts per gallon guideline is utterly useless. If you wanted light-loving clams and corals in this tank, I'd use a 250-400 watt halide (or equivalent). For the animals you have, I'd say that the 70 watt halide is on the high end of what you need in terms of light intensity. The animals care how much light is hitting them, and not how many gallons of water are in their aquarium. Watts per gallon is a guideline best forgotton IMHO

cj

 

[kenny2064]

thanks for the info was getting a little information overload while doing my research on what lighting to go with....so much information out there its sometimes hard to make decisions

 

[sogreedy23]

so i know that typically you want about 2+ watts per gallon for lighting my question is this would a 70 watt k2 viper be enough for a biocube 29 with a 14k bulb or would I have to substitute the bulb for a 20k bulb to compensate the low wattage...I think i understand the rule of thumb where kelvin is the spectrum of light where the wattage is the power while both are important would a 70 watt k2 viper be enough for a bc 29...i dont have sps at all have mixed zoas, blasto, shroom, a sunflower (i think) but let me know

Kelvin is independent of wattage and as Chris posted, Kelvin is pretty arbitrary. Watts per gallon is useless because depth is a huge part of PAR values and different Kelvin ratings produce different amounts of par. For the most part, blue bulbs will have lower par at an equal distance. 70 watts is going to be a little low and I'd personally say 150-250 should be the target for SPS and clams (150 being ideal for a nice mixed reef, 250 for SPS dominant). 70watts for your zoa/ softy tank is good for now, just know that you'll need to upgrade when you want to expand your corals.

I have my 70 w viper on my 7.5g cube and had it on my 10gal before I upgraded to T5s. Good luck on your new set up, gotta just keep reading man!

 

[tosiek]

The main factor (to make it easy to choose) you are looking for when choosing bulbs is their PAR ratings at different depths. Its not THE deciding factor on what lamp per depth and size of tank but it will help you pick the bulb needed for the tank if you can't decide what wattage to use. Things like 29g AIO tanks and small 20g breeders and the like are hard to get higher wattage setups ontop of them and because of the depths you can get away with less wattage setups like 70w vipers and such.

Purely as an example you can think of it as a 70w bulb 6" off the surace of the water @ a 7" deep point in the tank will give you par ratings equal to a 250w bulb 12" off the surface of the water @ a depth of 15-20". Along those lines. So you should be able to get away with keeping SPS or clams as long as they are within 8-10" of the 70w lamp and still meet the light intensities for the specific animals. 150w is what you want to shoot for in a 29g if you want to keep clams and SPS successfully anywhere in the tank for the most part.