Star Tortoises .net

StarTortoises.net

UVB & UVI Readings

Outdoor readings

All outdoor UV readings on this page were taken in the southern half of the U.S. using Solar Light Company's Solarmeters. These tables were created over a period of several years. Recordings in each table were done in a different month and/or year.

UVB was measured with the Solarmeter 6.2 digital UVB meter. It measures UVB in microwatts per square centimeter (µW/cm²). All UV index (UVI) readings were taken with the Solarmeter model 6.5. See the UV meters page for info on them plus an explanation of Ferguson zones used in in reptile lighting.

Tables 1-4 are UVB only readings.
Tables 5-6 are UVI only readings.
Tables 7-8 are combined UVB and UVI readings.

solarmeters 6.5 and 6.2

Solarmeter 6.2 (UVB) and Solarmeter 6.5 (UVI). Model 6.5, or the reptile labeled 6.5R, is the current standard for tortoise keepers.

Note: The UV chart on the face of the Solarmeter 6.5 above is NOT the reptile specific Ferguson zones chart, but a UV index scale (1-15) for humans to help avoid harmful exposure to UV radiation. Only the Zoo Med version and the new Solarmeter 6.5R version (R = reptile) have the Ferguson zone charts on the covers (not pictured). See the uv meters page for info.

Update 2020: Lugarti now also sells Solar Light Company's Solarmeter 6.5R under their label as the Lugarti Reptile UV Index Meter. It has the Ferguson zone chart on the front as well.

1.) UVB sky readings in May

For measurements in this table, the Solarmeter 6.2 UVB meter was pointed straight up at the sky (sky readings), but not directly into the sun (solar readings). Direct solar readings would be higher for UVB. Scroll down to charts with both sky and solar readings. Early May, sunny all day, DST time.

Format: Sky UVB readings are in µW/cm².

8:00 am = 30
9:00 am = 97
10:00 am = 165
11:00 am = 234
12:00 noon = 289
1:00 pm = 291 (highest UVB)
2:00 pm = 283
3:00 pm = 233
4:00 pm = 154
5:00 pm = 70
6:00 pm = 21

2.) UVB sky readings in Jul

Again, the Solarmeter 6.2 was pointed straight up at the sky, but not directly into the sun. Mid July, mostly sunny, but cloudy when noted.

Format: Sky UVB readings are in µW/cm².

7:00 am = 9
7:30 am = 20
8:00 am = 35
8:30 am = 68
9:00 am = 94
9:30 am = 160
10:00 am = 191
10:30 am = 102 (cloudy)
11:00 am = 127 (cloudy)
11:30 am = 120 (cloudy)
11:45 am = 246 (sunny w. clouds)
12:00 noon = 202 (sunny w. clouds)
12:30 pm = 346 (sunny w. light clouds)
12:45 pm = 356
1:00 pm = 356
1:15 pm = 360 (highest UVB)
1:30 pm = 348
2:00 pm = 327
2:30 pm = 305
3:00 pm = 275
3:30 pm = 232
4:00 pm = 191
4:30 pm = 152
5:00 pm = 109
5:30 pm = 72
6:00 pm = 47
6:30 pm = 23
7:00 pm = 12

3.) UVB sky & sun readings in Feb

For the following two tables, two separate UVB readings were taken with the Solarmeter 6.2 UVB meter. First, the UVB meter was pointed straight up at the sky (zenith). This sky reading value is listed first in the table. Then, the UVB 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 can 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 am and 8:00 am.

Temperature and humidity were also recorded. Temperature and humidity probe was placed in a shady spot just a few inches above the ground. Early Feb, sunny all day.

Order of values is: sky/sun UVB µW/cm² - Temperature °F - Humidity %.

7:00 am = 0/0 - 47 - 86
7:30 am = 4/2 - 47 - 85
8:00 am - 14/8 - 50 - 86
9:00 am = 46/57 - 57 - 80
10:00 am = 75/108 - 64 - 58
11:00 am = 133/164 - 70 - 45
12:00 noon = 151/193 - 75 - 35 (highest UVB)
1:00 pm = 141/187 - 71 - 43
2:00 pm = 92/125 - 72 - 44
3:00 pm = 60/88 - 73 - 39
4:00 pm = 22/28 - 72 - 40
5:00 pm = 4/2 - 69 - 40
5:30 pm = 0/0 - 68 - 42

4.) UVB sky & sun readings in Oct

Solarmeter 6.2 UVB meter. Readings format is sky / sun. Late October, sunny all day.

Order of values is: sky/sun UVB µW/cm² - Temperature °F - Humidity %.

6:00 am = 0/0 - 52 - 73 (dark)
7:00 am = 0/0 - 51 - 72 (lighter)
7:30 am = 1/1 - 52 - 71 (sunrise 7:12)
8:00 am = 8/6 - 55 - 71
8:30 am = 22/24 - 60 - 61
9:00 am = 38/53 - 63 - 50
10:00 am = 84/117 - 66 - 43
11:35 am = 156/186 - 67 - 42
12:00 noon = 172/201 - 69 - 46 (highest UVB)
1:20 pm = 179/189 - 71 - 43
2:00 pm = 165/187 - 70 - 44
3:35 pm = 72/86 - 73 - 33
4:00 pm = 41/73 - 72 - 33
4:50 pm = 20/11 - 71 - 33
5:10 pm = 10/9 - 70 - 33
5:35 pm = 3/2 - 70 - 35 (sun low)

5.) UVI readings in Dec

These UV index (UVI) readings were taken outdoors with Solarmeter 6.5 UVI meter in the southern part of the U.S. during the shortest day of the year (Dec 21). The meter was pointed at the sky. Sunrise was at 6:59 am and sunset at 4:51 pm. Weather was cloudy most of the day. Late December, mostly cloudy, but sunny when noted.

Order of values is: UVI - Temperature °F - Humidity %.

7:00 am = 0.0 - 50 - 83 (sunrise)
7:15 am = 0.0 - 50 - 83 (sun up)
7:30 am = 0.0 - 51 - 84
8:10 am = 0.0 - 51 - 83
9:00 am = 0.2 - 54 - 84
10:00 am = 0.3 - 55 - 82
11:00 am = 0.5 - 57 - 81
11:30 am = 0.9 - 58 - 80 (partial sun)
12:00 noon = 0.9 - 60 - 76 (highest UVI)
2:15 pm = 0.4 - 63 - 63 (sunny)
3:10 pm = 0.1 - 63 - 61
4:00 pm = 0.0 - 62 - 69

6.) UVI readings in Dec

These UV index (UVI) readings were taken in the southern part of the U.S. day after the shortest day of the year (above) with Solarmeter 6.5 UVI meter. Since the previous day was so cloudy, I took new readings on this sunny day with a clear blue sky (Dec 22). Notice how the UVI readings somewhat are higher than on the cloudy day before. Late December, sunny all day.

Order of values is: UVI - Temperature °F - Humidity %.

7:45 am = 0.0 - 51 - 73
8:10 am = 0.1 - 53 - 72
8:30 am = 0.2 - 55 - 69
9:00 am = 0.3 - 55 - 69
9:30 am = 0.4 - 58 - 68
10:00 am = 0.7 - 66 - 44
10:30 am = 1.0 - 69 - 36
11:00 am = 1.3 - 70 - 34
11:30 am = 1.4 - 69 - 33
12:00 noon = 1.5 - 68 - 37 (highest UVI)
12:30 pm = 1.4 - 68 - 38
1:10 pm = 1.2 - 68 - 36
2:05 pm = 0.7 - 68 - 34
2:30 pm = 0.4 - 67 - 35
4:00 pm = 0.0 - 64 - 45

7.)  UVB & UVI readings in Apr

UVB was measured with Solarmeter 6.2 (µW/cm²) and the UV index (UVI) with Solarmeter 6.5. Meters were pointed straight at the sky. These readings were taken at the very end of April on a warm, sunny day. Temperature and humidity were recorded as well. Late April, sunny all day with few clouds.

Order of values is: UVB - UVI - Temperature °F - Humidity %.

6:08 am = 0 - 0 - 51 - 49
6:15 am = 0 - 0 - 51 - 49 (sun rise 6:10)
6:30 am = 1 - 0 - 51 - 47
6:45 am = 3 - 0 - 53 - 46
7:00 am = 6 - 0 - 55 - 39
7:15 am = 12 - 0 - 57 - 37
7:30 am = 19 - 0.1 - 59 - 36
8:00 am = 34 - 0.2 - 63 - 33
8:15 am = 38 - 0.3 - 64 - 33
8:30 am = 52 - 0.5 - 65 - 33
9:00 am = 62 - 0.7 - 67 - 32
9:15 am = 121 - 1.5 - 70 - 32
9:30 am = 133 - 1.7 - 71 - 33
9:45 am = 162 - 2.3 - 72 - 33
10:00 am = 181 - 2.7 - 73 - 33
10:30 am = 212 - 3.6 - 74 - 31
11:00 am = 247 - 4.1 - 75 - 31
11:30 am = 278 - 5.0 - 76 - 27
12:00 noon = 295 - 5.6 - 81 - 22
12:35 pm = 330 - 6.4 - 85 - 20 (highest UVB)
1:00 pm = 329 - 6.5 - 88 - 19 (highest UVI)
1:30 pm = 299 - 5.6 - 91 - 18
2:00 pm = 304 - 5.6 - 89 - 18
2:30 pm = 274 - 4.8 - 86 - 18
3:00 pm = 225 - 3.8 - 83 - 19
3:25 pm = 201 - 3.1 - 81 - 20
4:00 pm = 167 - 2.3 - 80 - 20
4:30 pm = 122 - 1.4 - 78 - 21
5:00 pm = 93 - 0.9 - 77 - 22
5:30 pm = 49 - 0.4 - 75 - 24
6:00 pm = 33 - 0.2 - 73 - 24
6:30 pm = 15 - 0.1 - 72 - 28
7:00 pm = 5 - 0 - 70 - 30
7:30 pm = 0 - 0 - 68 - 34 (sunset 7:40)

8.) UVB & UVI readings in Jul

UVB was measured with Solarmeter 6.2 (µW/cm²) and the UV index (UVI) with Solarmeter 6.5. Two separate readings were taken each time. Meters were first pointed straight at the sky and then directly at the sun. Readings format in the table is sky / sun.

These readings were taken mid summer in July on a warm, but cloudy and unusually humid (for this area) day. Summer rain is not common here. The clouds were quickly moving, so the readings were changing fast between meter changes. Thus, the UVB and UVI readings were not always taken in perfectly matching conditions.

Temperature and humidity were recorded with a thermometer / hygrometer that was placed in a shady spot under a bush and a tree. Mid July, partially cloudy day.

Order of values is: sky/sun UVB - sky/sun UVI - Temperature °F - Humidity %.

6:40 am = 4/2 - 0/0 - 71 - 99 (sunny)
7:00 am = 9/5 - 0.1/0.1 - 71 - 99 (partly cloudy)
7:30 am = 20/13 - 0.2/0.1 - 73 - 94 "
8:00 am = 37/34 - 0.4/0.3 - 74 - 86 (mostly cloudy)
8:30 am = 73/89 - 0.8/1.0 - 78 - 80 (sunny)
9:00 am = 108/137 - 1.4/1.7 - 81 - 76 "
9:30 am = 93/94 - 1.5/1.4 - 82 - 69 (partly cloudy)
10:00 am = 84/89 - 1.4/1.4 - 81 - 72 (mostly cloudy)
10:30 am = 109/113 - 2.0/2.1 - 82 - 58 "
11:00 am = 258/260 - 5.2/5.7 - 82 - 56 (sunny w. clouds)
11:30 am = 315/324 - 6.5/6.7 - 83 - 54 "
12:00 noon = 345/349 - 7.3/7.2 - 86 - 46 "
12:30 pm = 349/341 - 7.8/7.7 - 86 - 47 (mostly sunny)
1:00 pm = 352/347 - 8.1/7.8 - 86 - 49 (sun, highest UVI)
1:30 pm = 348/329 - 7.9/7.4 - 85 - 49 (mostly sunny)
2:00 pm = 330/287 - 7.1/6.4 - 86 - 49 (sunny)
2:30 pm = 309/300 - 6.5/6.3 - 84 - 50 "
3:00 pm = 276/283 - 5.5/5.3 - 85 - 51 "
3:30 pm = 236/231 - 4.3/4.3 - 85 - 51 "
4:00 pm = 196/206 - 3.3/3.5 - 84 - 51 "
4:30 pm = 107/95 - 1.6/1.4 - 85 - 49 (partly cloudy)
5:00 pm = 84/61 - 1.2/0.9 - 86 - 47 "
5:30 pm = 33/24 - 0.4/0.3 - 82 - 54 (cloudy)
6:00 pm = 3/3 0.4/0.3 - 80 - 59 (dark clouds, no sun)
6:30 pm = -  -  -  - (rain started 6:10)


Related page: UV meters for reptiles

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