Bulb spectrum discussion

[Jeff120]

I am interested in the 6 bulb lot of 96W 6700K plant daylight. Let me know right before you order though.

I also have a question. Right now I have 12000K bulbs above my 125. Would the plants benefit more from 6700K bulbs?

My understand is that plants cant absorb the blue waves. 12000 is more of a white/blue then the 6700k-its a full spectrum. So in theory your plants should grow better in about 5000-10000K light. Someone correct me if I am wrong

[Cristy Keister]

Plants can most efficiently use red light, blue is second best, with green being the least useful. However, blue light penetrates deep water better than red light. So if you have a very deep tank you might try combining 64000k-67000k daylight bulbs with 10000k-12000k bulbs.

[tomterp80]

I'm interested in this discussion given my mission to improve lighting in my tanks. Here's an excerpt from the AH supply site, discussing bulbs. It includes saltwater applications but towards the end is general in nature, so I post the whole text. Also, somewhere I read that a bulb around 5000k enhances red in plants and fish, so I was thinking of including one bulb at 5000k among others that are around 6700k. Per AH supply:

** Bulbs with a Color Temperature of 5000K through 7800K are appropriate for freshwater planted aquariums. There is no practical difference regarding plant growth, but there is an appearance difference. Bulbs around 5000K have a warmer daylight appearance similar to early morning light. Bulbs around 6400K or 6700K have an appearance more like daylight in the middle of the afternoon under a clear blue sky. The 7800K bulb are just slightly bluer than the 6700K but maintain a balanced, daylight spectrum.

For marine aquariums, you'll want to mix 7800K or10000K bulbs with Blue bulbs in a ratio of 1:1 or 2:1 or use the Combo bulbs which have one tube that is 10000K and the other tube dark blue actinic.

For Blue actinic bulbs we provide a description rather than a color temperature so you'll better understand what appearance to expect. Those bulbs called Bright/Medium Blue put out most of their light between 400nm and 500nm. Those called Dark/Deep Blue put out most of their light between 380nm and 450nm. Both have their primary spectral peak at around 420-430nm. Actinism is a property of radiation which, in the visible spectrum, has wavelengths between 380nm and 500nm.

General compact bulb info:

The Rated Life of a bulb, as supplied by the manufacturer, is an average of how long the bulb will light. About 2% light for 180% of the rated life, about 2% light for 20% of the rated life, though by far the vast majority fall close to the manufacturers' averages. The rated life of most tri-phosphor compact fluorescent bulbs is 8000 to 12000 hours. For an aquarium application, the effective life is usually about 12 to 14 months -- or longer if your total lighting is high relative to the needs of the species in your tank, especially for freshwater setups.

The Color Rendering Index (CRI) for all 5400K and 5500K bulbs is 91-92. That's "excellent" in CRI talk. All other bulbs in the 5000K to 10000K range have a good CRI in the low 80's. A common Cool White fluorescent bulb usually has a CRI in the low 70's. That's considered "fair." CRI's below 70 are considered "poor." Note that CRI is irrelevant for marine setups when the aim is to simulate the appearance under many feet of water rather than to simulate the appearance of colors under full spectrum light. Blue actinic bulbs used on marine setups usually have a CRI in the 20's or 30's.

The difference between CRI 92 and CRI 84, for instance, doesn't mean that all colors are rendered with 8% less accuracy with CRI 84. It only means that certain colors that depend on the wavelengths that the CRI 84 bulb is lowest in will be rendered somewhat less accurately. It is likely that the CRI 84 bulb will supply all the wavelengths necessary to render all colors you are interested in very well. That's why a CRI in the 80's is considered "good."

A lumen is essentially a measurement of brightness to the human eye and is therefore very heavily weighted to the middle wavelengths of light that the human eye responds to most readily. As such, this measurement is not very helpful for aquarium applications since the middle wavelengths are the least important to aquarium inhabitants. To focus on lumens can be very misleading. For instance, the 55W 5000K bulb in the chart above has 4200 lumens while the 55W 6700K bulb has 4600 lumens. Yet these bulbs have the same total light output. The 6700K bulb simply has a little more of its output in the middle wavelengths.

[SCMurphy]

We have discussed this and similar topics a bit around here.

http://www.gwapa.org/forum/viewtopic.php?t=72

http://www.gwapa.org/forum/viewtopic.php?t=307

http://www.gwapa.org/forum/viewtopic.php?t=786

http://www.gwapa.org/forum/viewtopic.php?t=1065




14

[DelawareJim]

I agree with Cristy, a mix is best. The peak sprectrum for photosynthesis is roughly 420 nm at the blue end (like actinic 03 bulbs) and 680 nm at the red end. A curve showing peak utilization of the spectrum for photosynthesis shows a peak at 420 nm (blue), a valley in the middle (green) and another peak at 680-700 nm (red). The 680 nm wavelength is the most efficient for powering photosynthsis but also the less able to penetrate water than 420 nm. 420 nm is best for growing stocky, full, well balanced plants. 680 nm is best for fruit and flower production and tends to give leggy growth if used exclusively over time.

Your best bet is actually probably something on the order of a 4-bulb system with 1 actinic, 1 grow bulb (those funky pink things), and 2 daylight somewhere in the range of 6,700'K to 10,000'K.

Cheers.
Jim