UV or not UV?
Everything you need to know about UV
What is UV?
Light
UV or Ultra Violet is a type of lightning that is invisible for the human eye. As you probably know, light is electromagnetic radiation that moves in waves. UV has a very short wave length and thus a high frequency. Therefore UV contains a lot of energy and is even able to trigger chemical reactions in organic molecules.
Types of UV
There are 3 types of UV lightning. A, B and C. UV A  (wave length: 320-420nm) has the longest wave length which is able to penetrate glass. UV B (280-320nm) plays a big role in the regeneration of the earth's ozone layer. These waves cannot penetrate glass. The last type of UV, UV C (100-280nm), is very destructive to the skin. All waves with a wave length smaller than 100nm are known as Roentge.
UV and reptiles
Vitamin D3 and MBD
As told above, UV can trigger chemical reactions in organic molecules. When UV B comes in contact with the skin, production of vitamin D3 is triggered. This vitamin is crucial in the activation of calcium in the body. Calcium is needed to produce and maintain bony structures. When calcium from food intake is activated, the body can use it to build bones. In this way, metabolic bone disease (MBD) is prevented. But here is the danger: when the body gets vitamin D3 while there is no calcium intake, the vitamin will activate calcium from the body's bones and thus trigger MBD. The calcium will be pulled from the bones. Vitamin D3 can thereby prevent MBD and trigger MBD! Therefore it is super important to maintain the right balance between calcium and vitamin D3!
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Reptiles can maintain this balance by themselves by regulating their vitamin D3 production in the skin. But only if you offer them UV B lightning. They can decide to bask when they lack vitamin or go hiding when they have plenty. If you only provide D3 as a food supplement, you can overdose your reptile, causing MBD.
Communication
You might have forgotten about this part, but UV A lightning actually plays a big role in animal communication. We are unable to see UV, but other animals can! Like birds, reptiles and insects for example. Animals might look totally different to each other then they do to us, because we can't see their magical UV reflecting colors! These colors are only visible when UV light shines on their bodies. When you don't provide UV lightning, your animals cannot see these colors either and you take away a part of their vision and communication.
What with nocturnal reptiles?
"Nocturnal and crepuscular animals don't need UV lightning because they don't see daylight." WRONG! (Sun)light gets everywhere by bouncing from one object to another. Even shadow places receive a bit of light waves. The thing with nocturnal animals is that they are more efficient with the uptake of UV B in the skin. They do use it but they need less to produce the same amount of vitamin D3 compared to diurnal animals! This means they do need a UV bulb, but a different one from day active reptiles.
Cancer
Be careful with UV. Too much is never a good thing. If your UV bulb is too strong, your reptile might end up with cancer or burned skin. Therefore it is important to buy the right bulb for your reptile. The next paragraph shows you all you need to know!
Correct use of UV bulbs
Identification of my reptile
Different types of reptiles need different types of lamps. Their ecology determines their skin protection against sunlight and their efficiency in vitamin D3 production. Desert species can cope with the fierce burning sun while with shadow dwelling, tropical geckos cannot. Dr. Gary Ferguson made it easy for us by making a UV Index (UVI) with 4 zones.
Zone 1: 0.4 – 0.7 UVI (shade)
Zone 2: 0.7 – 1.0 UVI (mostly partial sunlight)
Zone 3: 1.0 – 2.6 UVI (mostly full sunlight)
Zone 4: 2.6 – 3.5+ UVI (midday full sunlight)
Therefore the first thing you have to do is to identify to which zone your animal belongs to. Crested geckos are in zone 1. If you are wondering about other reptiles, you can find a list here:
https://www.reptilecentre.com/blog/2020/09/which-ferguson-zone-is-my-reptile-in/
Correct lamp in the correct place
Not all UV lamps are the same. There is a large variety in TL's and bulbs on the market. Make sure you buy the lamp who provides the right Ferguson zone. The intensity of your UV light also depends on the distance between the lamp and the animal! The closer to the lamp, the higher the UVI. Always read on the box at what distance your animal should stay from the lamp. If it is harmful to be closer than 20 cm to the lamp, don't provide a basking spot 10 cm underneath the lamp. If the ideal distance is 20 cm from the lamp and you only provide a basking spot 40 cm underneath the lamp, it is not going to help either.
Testing
It is a bit vague to just believe the lamp is doing what it should while you can't actually see what it is doing. Light bulbs are not always doing what they should be doing accoring to the box. Therefore, you can measure the UVI with a solarmeter or a UVI radiometer. you can measure the intensity of your lamp at the distance you want. These things can cost up to €300 though. The cheapest way to measure the UVI is with a UV lamp testing card which has a strip that changes color depending on the UV intensity.