Читать книгу Blackwell's Five-Minute Veterinary Consult: Reptile and Amphibian - Javier G. Nevarez - Страница 42

Another challenge in selecting the proper UVB bulb is the fact that bulb strength or percentage UVB emission does not directly translate to its effectiveness in stimulating vitamin D3 synthesis in the body. There are in vitro models to assess the efficiency of UVB light (Burger et al, 2007) but these are impractical in a clinical setting. We must rely on the reputation of the manufacturer to ensure the bulb is of good enough quality. How much UVB a particular reptile species requires is another question, without a clear answer. In general terms, reptiles should have exposure to a minimum of 13–20 μW/cm² UVB irradiance with tropical species needing as much as 30–40 μW/cm², and desert species requiring as much as 150 μW/cm². Much research is needed to confirm this information, but it is a starting reference point. In nature, UVB exposure will vary with time of day, cloud covering, and so on, but in captivity the exposure level will be fairly constant while the bulb is turned on. Providing hiding places and a gradient of UVB light can help to reduce UVB overexposure although in practice overexposure is not as common of an event.

One practical option is to measure the UVB irradiance using a hand‐held radiometer. While expensive (approximately $250.00) these units are available to the general public. Their accuracy has been questioned, but they remain a good tool for the average reptile owner. A radiometer can be used to measure UVB irradiance of a bulb at any distance to determine how much UVB is being emitted and to record the decay of transmission over time. For example a 10.0 linear fluorescent bulb may emit 50 μW/cm² at 12 inches when first purchased but after 6 months, the irradiance at 12 inches may have decreased to 25 μW/cm². While this may still be acceptable exposure, it certainly indicates decrease in the bulb’s effectiveness over time. This decay is normal but if one desires to provide a more constant UVB exposure year round, it may be time to purchase a new bulb. They can also be used to evaluate the effect of the screen or mesh cover on the effectiveness of a bulb to help clients select the most appropriate bulb for their set‐up. Some newer radiometers measure ultraviolet index providing scale from minimum to very high while others provide readout based on the Ferguson zones to help determine the UVB exposure. These radiometers are advertised as being able to measure the appropriate UVB dose for vitamin D3 synthesis although that claim has not been verified.