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Burmese & Indian / Sri Lankan Star Tortoises
(G. platynota & G. elegans)

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Other Stars

• Starred tortoises
• Radiated tortoise

Angulate Tortoise
(Chersina angulata)

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Note: Not all reptile light bulbs provide UVB. Read the product info on the package carefully!

UVB Readings

w. Solarmeter 6.2

UVB reading on a sunny spring morning at 8 a.m. DST

Outdoor UVB - Spring (sky readings)

These readings were taken in the southern half of USA using the Solarmeter 6.2 digital UVB meter. The Solarmeter 6.2 measures UVB in microwatts per square centimeter (µW/cm²).

For measurements in this table, the UV meter was pointed straight up at the sky, but not directly into the sun. Direct solar readings would be higher for UVB. Scroll down to a comparison of sky/solar readings. Sunny all day (early May).

Highest UVB reading for that spring day was 291 at 1 p.m. DST.

Outdoor UVB - Midsummer (sky readings)

Again, the UV meter was pointed straight up at the sky, but not directly into the sun. UVB is measured in microwatts per square centimeter (µW/cm²). Mostly sunny, but cloudy when noted (mid July).

Outdoor UVB - Early spring (sky/sun readings)

For this table, two separate UVB readings were taken. First, the UV meter was pointed straight up at the sky (zenith). This sky reading value is listed first in the table. Then, the UV meter was aimed right at the sun (direct solar reading). This direct reading is the second UVB value in the table. In other words, the format is sky/sun.

Direct UVB reading shows the maximum UVB a tortoise may receive if basking in the full sun. Usually, the direct reading is higher than the sky reading, but this may be reversed around sunrise and sunset. For example, see the UVB readings at 7:30 a.m. and 8:00 a.m.

UVB is measured in microwatts per square centimeter (µW/cm²). Temperature and humidity are also recorded. Temperature and humidity probe is placed in a shady spot just a few inches above the ground. Sunny all day (early Feb).

Indoor UVB - Reptile lights

Active UV Heat MVB (5 mos old)

I usually hold the UVB meter 12" from the bulb. This is probably the most common reading distance among hobbyist (allows data comparison). However, to measure the amount of UVB your tortoise is actually exposed to, you'll need to hold the sensor at the level of your tortoise's back or head.

Above is the UVB reading under a 100W 5-month-old T-Rex "Active UV Heat" mercury vapor bulb (MVB). Note: This bulb is not same product as the T-Rex's newer, lower UVB output "UV Heat" bulb.

Reptile basking bulb

UVB reading under a 75W reptile basking bulb. This one is Zoo Med's "Repti Basking Spot Lamp." This type basking bulbs provide light, heat, and UVA, but no UVB.

ReptiSun 5.0 fluorescent bulb (1 yr old)

UVB reading under a one-year-old Zoo Med "ReptiSun 5.0" linear (long) fluorescent bulb. Fluorescent UVB bulbs should be replaced every six months or so, if you use them as your main UVB source.

Update: The newer thinking is that Solarmeter 6.5 UV index meter is actually more useful for measuring reptile UVB lights than the traditionally used Solarmeter 6.2. Solarmeter 6.2 reads the whole UV spectrum, while Solarmeter 6.5 is sensitive to the specific part of the UVB spectrum which creates vitamin D3.

Read more about reptile heat & UVB bulbs and the Solarmeter device on the lighting & heating page.