Perhaps someone could give me some more info on what a 6500k linear tube is used for. I spoke with someone briefly about it but my husband, being an electrician and all, thinks that a UVB linear tube can provide the same purpose as this light.
I need to know it's exact purpose and what does the 'k' stand for? Why is it 6500? .. Can I go without using one? I have some real plants in both of my enclosures but I want to make sure I'm providing my plants with sufficient a light source.
Any info is always appreciated. Thanks everyone!
Wow; its so hard to talk about light. As the previous respondent stated, the rating comes from "Degrees Kelvin"; Kelvin is usually used more in astrophysics than plant culture.
Yes, bulbs usually have a rating in degrees Kelvin. Color temp is only one aspect of the quality of light coming out a light bulb or tube. Others aspects are important in their own ways: spectrum, photosynthetically significant output, wattage, overall energy output, etc.
You will often see other terms that refer to light like lumens, lux, and microeinsteins per second per square meter. For plant lighting, you can ignore these. The wattage of the tube is significant. Longer tubes are better than shorter tubes. Closer is better. Direct light is better than filtered light.
Temperature of the bulbs is not critical. A 6500 K. is OK for plant growth, depending on the spectral output. Color temperature and spectral output are not tightly aligned. A "normal" light is a temperature nearer to 5500 K. This is sometimes referred to as a "daylight" bulb, as it is thought to be close to the color of an slightly overcast sky at mid-day.
Most of the bulbs that are optimized for plant growth have very little UV output; that is not what plants need. Plant lights usually have spikes in the outputs of the near-red and near-blue areas of their spectrums, because this type of light grows plants really well. "Gro-Lux" was a well-known brand of plant light. To our eyes, these lights look weirdly pink. For this reason, I prefer a daylight bulb such as "Vita-lite" or "Veri-Lux". They have a very white light. A 6500 K. bulb is a little "warmer", and most people seem to prefer this type of light.
Plants can use different wavelengths for photosynthesis, but they usually use the spectrum that comes from the sun best. Other areas of the spectra are less useful for plants. For instance, almost no plants use green light well. The same goes for mid UV, such as UVb. If the whole light output of a bulb was in the UVb band, plants would not grow well under them. As it happens, most of the bulbs we use for UVb have significant output in the bands that plants use for photosynthesis, so plants *will* grow under them.
With a combination of plant ( or daylight ) bulbs and UVb bulbs, everybody will be happy. This is what I use over my habitats.
Another huge factor for plant growth under lights is the quantity of light. For plants growing under fluorescent lights, more is better. Three or four 48" tubes is best for high-light plants, especially things like hibiscus. I use two or three Vita-lites to one Reptisun. For just plant growth, I use six T-5 tube fixtures; these are stunningly bright, especially before coffee.
For plant lighting, increasing the duration (daylength) can help make up for low light levels. A 16 or 18 hour day is fine for plants under lights. Tropical animals are not so flexible; they need to have a 12 or 12.5 hour day and so the longer period is not an option in their habitats. If you have a separate area for growing plants you might use longer days to get better growth.
The other major aspect of lighting for plant growth is distance from the light source. Light drops off very steeply from the source. Six inches is not half of three inches; its less. Closer is better. A deeper cage requires more light, or stronger lights to reach the floor.
Also, be sure to date your bulbs with an indelible marker with the installation date, and replace them every 6 months. Certain bulbs, like Vita-Lites will go for more than a year, but better to replace most types early. A meter can be invaluable here.
Hope some of that helps. Comments welcome.
