Last updated: December, 2009
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What is Ultraviolet Light?
To better answer that question I need to break down the spectrum into its parts, to demonstrate how it can be measured. Light is energy in the form of waves or particles that can be measured by specific meters and spectrometers.
This spectrum includes both the visible and invisible UV light, which depends on the length of the wave being presented which is measured in nanometers. The particular wavelength tells you the type of light, whether it is UV light or visible light, and if it is visible light and exactly what color it is.
The intensity or amount of light both the visible and invisible light are measured in microwatts per square meter (uW/cm2). Visible light can be measured in Lux or Lumens which indicates the brightness, or also in Kelvins which measures the warm or the color temperature of the light.
Technically on the nanometer scale, UVC emissions begin in the low 100 nanometers and go to 280 nanometers. The UVC wavelength emissions have no benefits to our reptiles and serve no purpose to reptiles other than to damage cells, and their DNA, causing death if the wavelength is low enough. The most common use of UVC is for sterilization methods such as lab and hospital equipment. Obviously, any lights that are tested with a good UVC meter and spectrometer and found to be emitting UVC emissions should be avoided at all costs.
The next wavelength emission is UVB, which is a very important spectrum of light needed by reptiles to help enable Vitamin D3 synthesis and to aid in helping to prevent Metabolic Bone Disease. UVB emissions begin at 280 nanometers and go up to 320 nanometers.
The wavelengths that are most important in Vitamin D3 synthesis are around 290 to 305nm. The body simply will not manufacture vitamin D3 without the proper UVB exposure.
The quantity of UVB emissions is portrayed by a UV meter which gives readings in µW/cm², or microwatts per square centimeter. This is simply the amount of UVB that the bulb is giving out when measured at a certain distance, so a reading might be 10 uW/cm2 at 12 inches, or 50 uW/cm2 at 6 inches, and so on.
It is virtually impossible to predict the exact number of microwatts needed per second, minute, hours or even daily for a dragon to meet his or her requirement of UVB exposure. What we can recommend, to ensure that they are receiving adequate UVB exposure, is to make sure that the UV light is a tested bulb from a reputable company and that is it regularly changed as recommended. The good quality flourescent tube bulbs need to be replaced every 6 or so months for optimal output. The compact flourescent bulbs tend to have a much faster decay rate than the tube bulbs and should be replaced every 4-5 months. The Mercury vapor bulbs of the best brands are normally good for 8-12 months on average. If the reptile is offered consistent good quality UVB lighting he will instinctively regulate his own vitamin D3 levels by determining how long he needs to sit in a certain spot.
The last ultraviolet emission is UVA, which is a very important part of the spectrum too. This begins at 320 nanometers and goes up to 400 nanometers. This is very visible light to reptiles from 350nm to 400nm. Although we can’t see it, it is a most important light for natural behavior in our reptiles. This wavelength of light stimulates feeding, breeding and basking behavior as well as a general overall sense of well-being.
Visible light is from 400nm to 750nm for humans but as stated before, reptiles can also see UVA from 350nm to 400nm.
Color Rendering Index
Reptiles, in general, and specifically bearded dragons do not do well under the warmer color temperature of lights such as Kelvin readings under 4500, because these lack colors at the blue end of the spectrum and the UVA, so to the reptile it must look like sunset all of the time. A sunny day outside is roughly 6500 Kelvin or possibly a bit higher, which means it is a cool temperature color. We do need to try and simulate as close to their light spectrum as we can. There is a chart called the Color Rendering Index or otherwise known as the CRI. This measures the quality of the light, or basically how well it lights up things in their true colors and is indicated on a scale of 0 to 100. Just to give you an idea pure sunlight is around 100 and a good quality household lightbulb or the natural daylight flourescent non-UVB tube is upwards to around 80-90 on the CRI chart. It will normally have 5000-6500 Kelvins too.