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Lighting Introduction to UV Lighting

Written by Tracie Kretzschmar, MS in February, 2008
Last updated: December, 2009

Many people have become very inquisitive regarding Ultraviolet Lighting. There is a lot of information to sift through to truly grasp the entire meaning of what UV is and how it relates to our reptiles and their health. I am presenting a very basic article on UV but it will give you an idea on how to make more of an educated purchase on your next UVB light as well as the remaining full spectrum lighting needs for your reptile too.

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.

Choosing lamps​

Non-UVB lamps​

Our goal should be to simulate the natural daylight or sunlight spectrum as much as possible.

I encourage the use of halogen lights when the proper wattage is used for the correct size of tank. They are incredibly bright and hot for basking. They do tend to put out a lot of heat so caution should be used with them and normally should not be used in tanks smaller than a 20 gallon.

Ideally, they should be controlled by a dimming thermostat, for safety. The natural daylight household bulbs that are of a bluish color should not be used due to their Neodymium coating which dulls the hues for the reptiles. It appears brighter to our eyes, but not to the reptile's eyes. The Neodymium is a coating that is put on to increase the color rendering index falsely giving it a perception of a brighter light but to reptiles, it blocks out the yellow hue on the light spectrum which is important for their activity. A regular household lightbulb is fine to use however, as they are very bright & do not have any coating on them like the daylight bulbs do. The Kelvin readings or color temperature for regular household light bulbs are relatively high.

The natural daylight fluorescent coils and the natural daylight fluorescent tubes are safe to use, put out little to no heat but will greatly increase the overall brightness of the tank.

So, it does take a good amount of planning to determine what type of lighting will best suit the setup that you will be using.

None of these daylight lamps produce UVB, though.

UVB Lamps​

There are several types of UVB lamp available to the consumer today. There are fluorescent tube bulbs, coil and compact lights and mercury vapor bulbs. The particular brands will not be discussed due to the lighting industry constantly revolving and changing and hopefully the standards will be improving. I will recommend that you read Frances Baines' article at the end of this discussion in conjunction with this article to study the brands of lamp, and which ones are not good and which ones are. She has so generously spent her time with me helping me with technical knowledge and learning. Her countless hours of testing, research, and writing reports do not go unnoticed and her expertise is incredible.

Here is just a little bit more on UVB lighting in general. The fluorescent tubes are generally speaking, lower UVB output bulbs and do not generate much visible light or heat at all, so a bright white basking light must be used in conjunction with a fluorescent tube UVB to enhance the full spectrum of lighting and heating for your reptile. It is also recommended that while the tube may continue to come on for well over a year, that doesn't necessarily mean that it is emitting usable UVB rays. Unless you are using a UVB meter and know exactly what the bulb is putting out it is best to replace a tube bulb of a good brand after 6 or so months for maximum output. The flourescent tube bulbs should not be placed any closer than 6 inches for safety as well. They should run 3/4ths of the length of the tank with the basking light very close to the tube, on one side of the tank so that the reptile gets UVB at the same time it is basking.

Mercury vapor bulbs are high-end lamps; good quality ones produce heat, light and high UVB. Normally most types produce enough heat just by themselves without any supplemental heating depending on the size of the tank and your setup or the time of year as well. It is recommended to use a bright white daytime non-UVB fluorescent tube or coil just to enhance the overall brightness without adding any additional heat. It is also noted that it is best not to use a mercury vapor bulb in tanks under 40 gallons as it can lead to overheating injuries. Always check the temperature at the basking spot and in the cool end, with ANY reptile lighting.


UV lighting is quite complex and does take some planning in order to enhance the health of your reptile and keep him healthy. It is best to always do the proper research prior to purchasing your dragon or reptile so you can have the correct bulb in place before ever getting him. It will save a lot of heartache once you have your reptile. Also, Frances Baines' website and lighting charts can help you make a more educated decision on what lighting is the best and which ones you should avoid. That alone will save you a lot of time and money, so, please make sure to read her lighting information. A good rule to follow is that you normally get what you pay for, so if the UVB light is cheap and an unknown brand and not listed on her site or recommended by us, then it may not be very good or even potentially harmful. You do get what you pay for when it comes to UVB lighting.

To view Frances Baines' website please go here: UV Guide UK - Ultraviolet Light for Reptiles - UVB reptile lighting on test
Special thanks to Frances Baines' contributions for me.

Tracie Kretzschmar, MS
BD .org
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