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Lighting Introduction to UV Lighting

Written by Tracie Kretzschmar, MS

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 visible and invisible UV light, which depends on the wavelength measured in nanometers. The particular wavelength tells you the type of light, whether it is UV or visible light, and if it is visible light and exactly what color it is.

The intensity or amount of visible and invisible light is 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 warmth or the color temperature of the light.


Technically, UVC emissions begin in the low 100 nanometers on the nanometer scale 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. Any lights 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, a crucial 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 most important wavelengths in Vitamin D3 synthesis are around 290 to 305nm. Therefore, the body will only manufacture vitamin D3 with proper UVB exposure.

A UV meter portrays the quantity of UVB emissions, which gives readings in µW/cm², or microwatts per square centimeter. This is simply the amount of UVB that the bulb gives out when measured at a certain distance so that 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, hour, or even daily for a dragon to meet their 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 it is regularly changed as recommended.

The excellent quality fluorescent tube bulbs must be replaced every six or so months for optimal output. Compact fluorescent bulbs tend to have a much faster decay rate than tube bulbs and should be replaced every 4-5 months. The Mercury vapor bulbs of the best brands are typically good for 8-12 months on average. If the reptile is offered consistent good quality UVB lighting, he will instinctively regulate his vitamin D3 levels by determining how long he needs to sit in a particular spot.


The last ultraviolet emission is UVA, a vital part of the spectrum. 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 our reptiles' most essential light for natural behavior. This wavelength of light stimulates feeding, breeding, and basking behavior and 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 an excellent temperature color. So we need to try and simulate as close to their light spectrum as possible. There is a chart called the Color Rendering Index, or the CRI. This measures the quality of the light, or how well it lights up things in their true colors, and is indicated on a scale of 0 to 100. To give you an idea, pure sunlight is around 100, and a good quality household lightbulb or the natural daylight fluorescent non-UVB tube is upwards to around 80-90 on the CRI chart. It will typically 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 halogen lights when the proper wattage is used for the correct tank size. They are incredibly bright and hot for basking. However, they tend to put out a lot of heat, so caution should be used with them and typically 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 of a bluish color should not be used due to their Neodymium coating, which dulls the hues for the reptiles. As a result, 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. Still, to reptiles, it blocks out the yellow hue on the light spectrum, which is essential for their activity. However, a regular household lightbulb is acceptable, as they are very bright & do not have any coating like daylight bulbs. In addition, 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 and put out little to no heat. Still, they will significantly 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 lamps 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; hopefully, the standards will improve. However, you should read Frances Baines' article at the end of this discussion in conjunction with this article to study the lamp brands and which ones are not good and which are. She has generously spent her time helping me with technical knowledge and learning. Her countless hours of testing, research, and writing reports and incredible expertise have not gone unnoticed.

Here is 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. So, a bright white basking light must be used in conjunction with a fluorescent tube UVB to enhance the full lighting spectrum 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 it emits usable UVB rays. Unless you are using a UVB meter and know precisely what the bulb is putting out, replacing a tube bulb of a good brand after six or so months for maximum output is best. The fluorescent tube bulbs should also be placed at most 6 inches for safety. 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. Typically most types produce enough heat just by themselves without any supplemental heating depending on the tank size and your setup or the time of year. It is recommended to use a bright white daytime non-UVB fluorescent tube or coil to enhance the overall brightness without adding 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 takes some planning to enhance the reptile's health and keep him healthy. It is best to do the proper research before 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 decide what lighting is the best and which you should avoid. That alone will save you time and money, so please read her lighting information. A good rule is that you usually get what you pay for, so if the UVB light is cheap and an unknown brand is not listed on her site or recommended by us, it may not be very good or potentially harmful. You do get what you pay for when it comes to UVB lighting.

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

Tracie Kretzschmar, MS
First release
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