Star Tortoise Garden @
Star Tortoise Garden @

Indoor UVB Lighting

Sun is best

The best UVB source for tortoises is the sun. Tortoises really ought to have an outside enclosure, even if they can only use it part time. In addition to the necessary UVB exposure, outdoor exercise, like walking and climbing, is immensely important for tortoises' well-being. Weather permitting, let your adult and subadult tortoises roam outdoors as much as possible and take young ones outside for shorter outings.

If you live in a warm climate and your tortoise spends most of his days outside with free access to the sun, you won't need to use UVB bulbs if he's briefly housed indoors. Cost of UVB = $0.

On the other hand, if you live in a cooler climate with a short outdoor season, it's important to use reptile UVB lights indoors in addition to non-UVB basking bulbs and heaters.

Indoor basking & UVB

Star tortoises and other grassland (dryish area) species need access to hot basking areas and UVB to stay healthy. The UV output of reptile bulbs varies. Some of them provide both UVA and UVB, while others only supply UVA or no UV at all. Check the box labels.

The whole body of the tortoise should be warmed by the basking bulb, not just a small spot on top of the shell. If your tortoise is big, you’ll need a large heat panel or a group of heat lamps to cover a wide enough area.

You can provide UVB with long reptile UVB fluorescent tubes, reptile mercury vapor bulbs (MVB's), or the new reptile metal halide UVB lamps.

Place the basking bulb(s) and UVB source(s) at one end of the enclosure. The other end should always provide a more shaded, non-UVB area for the tortoise to retreat to as needed.

The UVB area should be a large zone from the most to least intense radiation. UVB should be at the max under, or right next to, the basking bulb(s) and then taper of to nothing over a large area. Just like with basking, the whole body of the tortoise should be covered by the UVB light, not just a little spot on the shell.

Lamp safety

1.) Quality

When purchasing UVB lights, always buy good quality reptile specific bulbs from trusted manufacturers like Zoo Med and Arcadia. Zoo Med is an American company and their products are easy to find. Arcadia is a European brand and their products are still harder to find in the USA.

Cheap copycat bulbs of unknown brands can emit dangerous UV radiation, for example, a too high level, the wrong wave length, or the wrong type. Tortoises need UVA and UVB, but not UVC which is harmful to them.

It's best to buy UL listed and prewired reptile lighting and heating products. Any DIY electrical wiring can be a fire hazard. Unless you know what you are doing. :0)

2.) Follow manufacturer's instructions

Always attach lighting and heating devices securely and according to the manufacturer's directions. Improperly installed tortoise enclosure fixtures can become loose and fall off causing a fire. House and garage fires have started this way.

Also, do check the minimum installation height for your specific UVB lamp and the recommended Ferguson UVB zone (see UV meters page) for your species.

3.) Lamp stands & brackets

Zoo Med reptile lamp stands work well with most dome type light fixtures. These stands have a little foot plate that goes under the enclosure to keep it in place. They are adjustable in height and depth and allow you to position lights exactly where you want them. They come in two sizes. I like the bigger stand, model LF-20, better because it has a larger foot that makes it more stable.

Other types of reptile lamp holders include Exo Terra's Light Holder Bracket and Repti Zoo's Dome Lamp Brackets for 2 lamps. These holders attach to the side of the enclosure.

4.) Caution with clamp lamps

Avoid attaching light fixtures by their clamps. Clamp fixtures can slide down to one side, or even fall off, and start a fire. Using a reptile lamp stand (see above) and a light fixture that has a metal hanging loop is a safer way to install lights. If you absolutely have to use clamps, try double securing them with welding clamps. Welding clamps have a very strong grip, but other extra heavy duty steel spring clamps work as well.

5.) Wall hooks & brackets

UVB and heat lamps can also be installed securely by suspending them from sturdy ceiling hooks or wall brackets. Light fixtures that have built-in hangers, for example, domes with metal loops on the top, are easiest to use. Lamps should not be hung by their cords.

6.) Smoke alarms

Keep hot bulbs away from any flammable materials like plastic enclosure covers or nearby curtains. Do install smoke alarms in your tortoise room, garage, basement, or wherever you keep your heated indoor enclosures.

reptile UVB fluorescent tube sizes

Linear (long) reptile UVB fluorescent tube sizes. T-12 with a 1 1/2" diameter is the oldest size, T-8 (1") was the common size before the new T-5 HO tubes (5/8") were released. Reptile T-5 HO tubes are stronger and put out twice the light and UVB of the older the T-8 tubes.

MVB's, long UVB tubes, and deep domes

MVB UVB bulbs of different brands are not all the same size even if they are the same wattage. Two 100W MVB's are shown with small and large deep domes (top left). Zoo Med reptile lamp stands are great for hanging lights on tortoise tables and tubs (right). I use the larger size stands. Zoo Med T-5 HO UVB tubes and a light fixture (bottom left).

Long T-8 UVB tubes (old style)

Zoo Med's ReptiSun fluorescent UVB tubes have been popular for years. They are available as 2.0 UVB, 5.0 UVB, and 10.0 UVB bulbs. For grassland species like star tortoises, the 10.0 bulb is better than the weaker 5.0.

Most tortoise keepers have switched from the old style T-8 tubes to the newer, stronger T-5 UVB tubes, especially in larger enclosures. Due to their higher UVB output, T-5 tubes can be installed higher above the tortoise.

Long T-5 UVB tubes (current style)

Two well known brands of the newer T-5 HO (high output) UVB tubes for reptiles are available in the US: Zoo Med and Arcadia. These T-5 HO UV tubes will not fit in the old style T-8 fixtures. They require T-5 specific fixtures.

1.) Arcadia T-5 tubes (update 2011-2012)

Note: Arcadia items are still harder to find in the US, but Reptile Basics sells Arcadia products, including UVB lamps, on amazon.

2.) Zoo Med T-5 tubes (update Nov 2012)

3.) Zoo Med LED UV hoods (update Apr 2014)

UVB tube fixtures & reflectors

I use Zoo Med and Arcadia fixtures for my UVB bulbs, but shop light and strip light fixtures can also be used to hold the long UVB fluorescent bulbs. Always check the size info to see if the fixture is made for the older, fatter T-8 tubes or the newer, thinner T-5 HO tubes.

Using reflectors with UVB bulb fixtures maximizes the light and UVB output by directing it all into the enclosure. Always check the minimum installation distance on the box to keep the UVB at a safe level for your tortoise. Ideally, use a UVI meter as well to create the appropriate Ferguson UVB zone for your species. See UV meters page.

long T-5 HO fluorescent UVB tubes

T-5 HO fluorescent UVB lamps for reptiles by Zoo Med and Arcadia. Fixtures photographed in 2012. Current models may differ.

Compact (short) UVB bulbs

Compact reptile UVB bulbs are short fluorescent bulbs that usually, but not always, screw in just like regular light bulbs. They can be straight or coiled (spiral) in shape. For tortoises, long UVB tubes are preferred over these compacts.

Compact UVB bulbs have created a lot of controversy among tortoise hobbyists. Some keepers say there are fine to use when properly installed overhead, while others swear compact bulbs have caused severe eye problems, even blindness, to their tortoises.

Potential problems with compact UVB bulbs:

1.) Possible eye damage

Some years ago, several reptile keepers reported eye problems in their animals due to the very intense UV radiation from some compact fluorescent bulbs at short distances. These bulbs have now been replaced with new, improved designs. Read the 2007 special report [offsite] by UV Guide UK.

2.) Small UVB zones

Even the best quality compact fluorescent UVB bulbs are not the best choice for tortoises because they cannot provide large enough UVB zones at sufficient intensity. The UVB gradient is intense: too strong and possible harmful at close distance and too weak at a usable distance. (Source: Dr Baines, UVB Meter Owners group)

3.) Possible initial UV spikes

Compact fluorescent bulbs, especially older models, may have an initial burn-in period when the UVB output is higher than normal. For example, with the older Zoo Med compact bulbs the period of high light and UVB output lasted about 150 hours. During that time, it was best to place the bulb higher than usual or to preburn it away from the tortoise enclosure.

Mercury vapor bulbs (MVB's)

Just like with the compact fluorescent UVB bulbs, there has been manufacturing problems with mercury vapor bulbs (MVB’s) in the past. For example, some MVB's from batches JI, KI, LI produced after Oct 2009 were affected. These defective MVB's emitted abnormally short wavelength UVB radiation and increased the risk of an eye problem called photo-kerato-conjunctivitis. (Source: UV Guide UK)

Several brands of MVB's are on the market, but it's safest to stick with respected, well known ones. Zoo Med's PowerSun UVB bulbs (80w, 100w, 160w) and Arcadia's lamps are are popular.

Update 2022: Arcadia recently released a new MVB bulb, the "D3 Evo Basking Lamp." This bulb was specifically developed for the 110-120v USA and Canadian markets and not converted from European 240v bulbs like other MVB's. According to Arcadia, this totally new design eliminates the problems that have plagued US MVB's previously.

1.) MVB dimensions

Not all MVB's are the same physical size. In other words, MVB's of the same wattage from different manufactures can vary in depth and width. Wider bulbs create larger basking areas which is good.

2.) MVB fixtures

MVB's are wider and deeper than regular household bulbs, so they require larger light fittings. Because MVB's stick out when placed in traditional reptile bulb holders, I like to use the larger 8 1/2 inch Zoo Med's Deep Dome or Fluker's Sun Dome fixtures with them. These two domes are almost identical; only the hanger wire shape is different.

Larger deep dome style bulb holders are long enough to totally cover MVB's. They also have a hanging loop which makes it easy to install them. No slippery clamps. They work well with reptile lamp stands.

You can also use work lights, utility lights, or brooder lights to hold reptile bulbs, although many of them are too shallow for MVB's. Utility lights can be equipped with fastening clamps, hanging hooks, or both. Utility lights usually have a high wattage rating.

MVB's should always be positioned vertically, in other words, straight down. Not at an angle.

3.) MVB wattage

MVB's have high wattage, typically 100-275W, and they get very hot. Thus, they may not be suitable for very small enclosures. Placing them in high humidity vivariums can be problematic as well.

Do check that your light fixture takes the high wattage of your MVB. For example, deep dome type fixtures are rated for 160W max and mini deep domes for 100W max.

4.) MVB installation height

Do follow the MVB installation instructions on the packaging. Do not position the MVB lower than the minimum distance recommended by the manufacturer. Typically, the MINIMUM installation distances are: 100W flood MVB at 12" (30 cm), 160W flood MVB at 18" (46 cm), and 275W flood MVB at 24" (61 cm).

Adjust the bulb position up or down, but above the minimum installation height, to achieve the ideal basking temperature. If the basking area is too hot, you can lift the bulb higher. If the area is too cool, you may need add a second basking bulb or switch to a higher wattage MVB.

Measure the minimum distance from the top of the tortoise, not from the ground. High wattage MVB's can get very hot and burn the tortoise if placed too low.

Ideally, use a Solarmeter 6.5 to measure the UVB output (UVI) and adjust the bulb height according to the Ferguson zones (see UV meters page) as well.

5.) Don’t shake MVB’s

Avoid touching, bumping, or moving MVB's to prevent an early burnout. It's best to hang up MVB's and not place them on top of screens that get opened all the time.

If a MVB goes off by itself, wait a few minutes. These bulbs can turn off when they overheat and will later turn back on by themselves. That is, if they are not burned out. Also, after being switched off, MVB's will not relight for at least a minute.

6.) Not for vivariums

MVB's are sensitive bulbs and may not be suitable for high humidity vivariums like those used to raise star tortoise babies. MVB's can also get way too hot for such small, closed areas. If you do install an MVB inside a vivarium, use a fixture that allows the air to circulate freely around the bulb to prevent heat build up. Better yet, use a long UVB tube with an incandescent basking bulb instead.

7.) Encourage pyramiding?

Some star tortoise keepers have noticed that baby star tortoises raised under hot MVB's may pyramid more severely than when using basking bulbs with more gentle heat. To combat this effect, run the MVB bulb for a only few hours in the middle of the day. For the rest of the day, use an incandescent bulb for basking. Also check that the MVB is not placed too low and too close to the tortoise's top shell to avoid shell burns.

Metal halide lamps

Metal halide reptile UVB bulbs are newer to the market. They provide visible light, heat, UVA, and UVB and are considered to be superior to MVB's. Metal halides' light output is bright and naturalistic. Unfortunately as of this writing, their beams are narrow and the UVB decays fast.

Two examples of these lamps are the Zoo Med's Powersun H.I.D. Metal Halide lamp and the Exo Terra's Sunray lamp. They must be used with metal halide lamp specific fixtures. Dr Frances Baines and others have started testing these bulbs. You can read their findings and recommendations at the Facebook Reptile Lighting group.

Web links

Related pages: UV meters, UVB readings

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