Reptile & Amphibian Forums

From the uv meter group:

> Should the 10.0 bulb give higher output?
That is the funny thing about percentage
10.0 means 10% of the output is uvb.

So if a lamp has a total radiative output of 9W (which is reasonable
for a 23W tube), of which 3W are UVA and 0.6W are UVB than the lamp has
0.06W/9W*100% = 6.7% UVB (and 30% UVA)

If you now choose to use a less efficient visible phosphor and only get
a total output 6W instead of 9W you end with 0.06W/6W*100% = 10%.
Magic - without increasing the amount of uvb you changed the tube from
6.7% UVB to 10% UVB.

What do we learn from that? Percentage of UV does only tell you
something about the relative distribution of energy in the spectrum of
the light. It does not tell you anything about intensities.

If you keep in mind that tubes only emit visible and uv radiation but no
infrared and you calculate the percantage of uv from the sun on this
basis (not taking the full spectrum of the sun as a reference but only
the visible and uv radiation) you get something between 0.1% to 0.8%.
Skylight at noon on the other hand has something like 2.5% UVB.

So fluorescent lamps generally have a very unbalanced spectrum with far
too little visible light. Apart from their colour their amount of uvb
matches more closely skylight than sunlight (as does their homogenious
distribution of light in space).

This is a very good question!

Firstly, the 5.0 and 10.0 were first devised to indicate, roughly, the percentage (5% and 10%) of UVB from the lamp - as a percentage of total UV plus visible light. It is a fairly pointless figure. And as Sarina points out, this can be manipulated - intentionally or otherwise - simply by altering the amount of visible light.
This was started with fluorescent tubes... So the early production boxes had printed on them something like: 5%UVB 30%UVA (and therefore, they were supposed to be 65% visible light).

What happened then, was that these figures became "legendary" and everyone started putting 5% or 5.0, and later, when stronger phosphor blends were used, 10% and 10.0.
Some lamps - such as the ZooMed and Arcadia ones - did actually match these percentages reasonably well..(and still do, for the TUBES at least. I tested some ZooMed Reptisun tubes last year and the figures from the spectral analysis were:
5.0 tubes - UVB 6.3% UVA 22.8% visible 71.2%
10.0 tubes - UVB 9.1% UVB 23.7% visible 67.4%
The figures have been rounded to one decimal place so don't add up to exactly 100%)
Some other companies have not matched the figures with anything like as much accuracy. As phosphors are changed, the percentages - especially of UVA- vary. Most lamps have nothing like 30% UVA nowadays... and the amount of visible light has also altered a lot, since many tubes now have tri-phosphors instead of the older halophosphate.

However... once you get on to the compact lamps the 10.0 and 5.0 names become just names. It's very unlikely that a compact lamp will be 5% or 10% UVB, because compact lamps have much more intense visible light, for a start.

The other problem is that ZooMed have been changing their specs over the last couple of years.
I suspect that your Reptisun 5.0 Compact Lamp is the older specification (this has a phosphor with a much higher proportion of its output in the shorter wavelengths) whereas your Reptisun 10.0 Compact Lamp is one of the new generation, which has a much safer spectrum, closer to that of natural sunlight in the UVB range.

Here are the percentages from some of the Reptisun compacts from both "generations"..

OLD TYPE Reptisun 5.0 Compact: UVB 9.5% UVA 11.2% Visible 79.5%
OLD TYPE Reptisun 10.0 Compact: UVB 25.9% UVA 23.5% Visible 51%
NEW TYPE Reptisun 5.0 Compact: UVB 3.9% UVA 10.9% Visible 85.2%
NEW TYPE Reptisun 10.0 Compact: UVB 6.3% UVA 16.5% Visible 77.2%

Now, lets move on to your Solarmeter 6.2 readings.
The Solarmeter 6.2 reads the total UVB - a broad band of wavelengths, that includes some longer wavelengths that are "safe" but produce only a little vitamin D3; middle wavelengths which produce good vitamin D3, and very short wavelengths which do produce D3 but which also are much more hazardous and can burn skin and eyes.
The old-type Reptisun compacts produce much more of the very short wavelengths. They give higher readings on the Solarmeters - but the UVB is not as "safe". (The UVB from the old-type 10.0 compacts was so 'strong' in brand new lamps that at close range it caused harm, in fact.)
This is why ZooMed changed to a safer specification. Their new generation of lamps give lower meter readings; but the light does not contain any of the hazardous, very-short-wavelength UVB which is not found in natural sunlight.

I've had a look at my own readings; those of Kevin's (great photos on your post, Kevin) and yours, Louis...
Kevin's readings are from tubes, so this makes direct comparison rather difficult.
Louis - how did you take your readings? Were they from the side of the compact lamp, (ie. with the lamp not in a dome) or were they from underneath, ie. with the lamp hanging down, and the meter aimed up at the "end" of the lamp? Or was the lamp inside a dome, and measured from below?
All these will make a lot of difference to the readings.
Here are my readings from a new-style Reptisun 10 Compact at 12", after 105hrs of use:
from the side - 25uW/cm2
from below - 9 uW/cm2
from below in ZooMed "deep dome" - 20uW/cm2

The requirements of different species are best met by trying to re-create the species' favoured micro-habitat in the vivarium. So if you know where the animal lives in the wild, and its basking habits (or not as the case may be) you can judge its likely choice of UVB exposure (eg. basking in morning sun only; never basking; sitting in full sun at any time of day; getting small amounts of sunlight filtering into its daytime sleeping position..etc)and a basic concept is to provide a similar gradient (from the maximum naturally chosen when basking, to virtually zero in the animal's sheltered area)so the reptile can freely decide what UVB it obtains.
But the lamp you choose will depend as much upon the size and type of housing, and its heating arrangements, as upon the species' requirements. You can't use a mercury vapour lamp, obviously, over a tiny vivarium and it's very impractical to use a fluorescent tube for sun-basking species in a large enclosure....

The other difficulty is in using the intensity in uW/cm2 (eg. as given by the Solarmeter 6.2) as the tool for choosing your lamp. Because all lamps have different spectra, if you have even two very similar lamps (eg two fluorescent tubes) giving readings of, say, 100uW/cm2 these lamps may have a completely different vitamin D3-producing potential from each other and from 100uW/cm2 of sunlight.
But there are ways round this.

Thanks
an interesting post!

Thanks Mightybd.

As far as the solar glow I have been using...

Hello Wayne,

do you have an ExoTerra SolarGlo? Their radiation varies very high... some are almost "killers" others should not be called "UV-lamp".
I wrote an article trying to subsume Frances' knowledge and my own readings of about 200 german lamps within a few pages.
It was written in german, but I tried to translate it in english.

I would be very interested in your all opinions and critique on the article (also if "my english" is plain .

This is the link:
http://groups.yahoo.com/group/UVB_Meter_Owners/files/Current recommendations on UV-supply of reptiles.doc

Best wishes from Schwelm,
Ingo

Many have confirmed what I said about that mv bulb Im using...

the bulb varies a great deal in light production and intensity and needs be tested before use.

My particular bulb runs on the very lean not too intense side.

Roughly a uv index of 1.2 - 2 max.

This uv radiation intensity does not put the animals at harm. Especially in a 4 foot long enclosure with plenty of hides.

I have not read his article yet.

Alright I read all of that post, and still wonder what bulb is the right one for bearded dragons. I use a exoterra solar glo 125W at 14" some of you put them within 12" or less, when I do that I get 130F temp readings.For my smaller dragon I use a reptisun 10.0 18" tube 12" high and I don't use a screen on either of them. What is the best bulb to use and how far away is right? What do use and what do recomend? My vet says the only one to use is the powersunUV through a screen at 12" to 16". She highly reccomend real sunlight for 30minutes twice a week. What do you use?
Thanks

I've always used Zoo Med 10.0 Linear Tubes about 12" from the basking spot. I've had many dragons radiographed over the years and they always had good bone density. Linear tube distribute light and UVB over a much larger area. Increased light makes dragons more active and promotes appetite.

I use Mega Ray bulbs for my Iguana.

Well what size/type bulbs depends on what size enclosure your trying to heat and what ventilation it has.

I try to create a nice gradient. The powersuns are decent but need to be all the way on one side of the enclosure with enough room for them to get well enough away from the bulb if they so desire.

Your surface temps directly under the bulb will approach the 130 mark. Should not be over that. And the size of the enclosure factors in yet again.

If your using smaller than a 2 foot high by 4 feet long by 3 deep you will need to increase the distance from the 125 watt bulb.

The 125 watt is a good bulb along with a florescent strip light for that size enclosure.

Why dont you try a 100 watt mv bulb instead of the 125 watt and move it slightly closer. Surface temp about 120.

It's all about gradient. The dragon will self regulate in the right setup with hides and a spot to absorb sufficient uvb.

I have talked to some breeders who have told me they dont use uvb at all. They use d3 supplementation and calcium supplementation and tell me they have had minimal issues.

So a lot is left to conjecture.

Trying to simulate the animals natural environment is the best.

A metal shroud around a mv bulb almost doubles the intensity directly under the bulb, and limits off a good portion to the sides.

This may be an option at distance to get more from the bulb but keep your temps in check.

You will need a nice brushed aluminum shroud to get the optimal results using this method and watch your distance if you shroud.

If you're using a shroud now with your surface temps being high you may consider drilling a bunch of holes in the shroud to let heat dissipate.

The surface temp directluy under the bulb is different than the ambient. This surface temp is always ging to run high directly under the bulb. The dragon is not going to wallow in that spot once it heats up. They will sit off to the sides.

In a dragon book I have the guy goes to Australia... after the dragon darts off his/her basking spot the guy quickly checks with a temp gun and it was 140 degrees.

Ambient on the hot side of the enclosure should be roughly between 100 - 110.

Ambient (air temp) on the hot side should be in the low 90's (90-92)

Proper basking (surface temp) for Bearded Dragons is about 105 for adults and about 110 for babies. Anything higher and the dragon will not bask and therefore will not get the benefits of UVB.

Those are low basking temperatures in relevance to nature. 105 is barely warmer than my body temperature. On a warm or hot day in the summer, the sun can burn flesh in 10 minutes. Think about it.

Bearded dragons are opportunistic baskers, not sun-loving desert creatures. Basking at higher temperatures affords them more time to search for food and shelter, and less time to become prey. Basking at lower temperatures means they will have do be exposed at ground level or above for longer periods of time and subject to more predation.

If 105 degree basking temps has brought you tremendous success with your dragons by all means, keep rockin. I think 120/130 temps make more sense though.

Captivity is not nature. The basking and ambient temps. I advocate in captivity have been proven over the decades.

Consider the origin BDmaster, they live in nature. A well thought out captive environment should be a replication of their natural environment.

With time and experience you will learn that the only way to duplicate the outdoor conditions is to house your animals outdoors. Now that seems pretty obvious to me.

I have seen and experienced the shortcomings of the "trusted" and "tried" methods.

It is all about gradient. Creating an environment that allows for the animal to self regulate at its own discretion.

This means creating a range from the maximum naturally chosen when basking and slightly above, (nearly a uv index of 4-5 for dragons) to virtually zero in the animal's sheltered areas or hides.

This so the reptile can freely decide what UVB (and heat) it obtains.

The sun is FAR hotter and more intense than we recreate in the artificial enclosures. FAR hotter

105 or 110 basking is good but that is like most likely providing them with a about a uv index of 1-2 or maybe 3 at most. That is stretching it.

So now you have provided them about 1 third of what they are able to access in the natural wild environment.

How is this best practice?

It is not.

If the dragon is literally (basking constantly) in the light/heat you provide. This means it is not hot enough and they should have access to more heat. 130 is about the max but access to a 120 surface temp is good. They may never use it but it's there if they so desire.

Gradient:

Zone 1: crepuscular or shade - UVI 0.7
Zone 2: partial sun or occasional sunbathing - UVI 1.0
Zone 3: partial to full sun - UVI 2.6
Zone 4: mid day baskers - UVI 3.5 and more

In other words...

105-110 surface basking is way too cool.

My armpit is hotter.

The UVB outage of even the best UVB producing bulbs in the market don't match what is available outside in natural sun. So having a hotter basking spot doesn't make any difference to the level of UVB available in a captive indoor environment.

The main reason having a basking temperature available that can reach around 120F is to provide a quick warm up for the dragons. I personally feel having a range of basking temps available is far more important than what temperature a single basking spot has. A dragon should have the option to move from temperature to temperature within its basking areas, not limited to one or two temperature zones.

The main disadvantage of a very high basking spot is the dragon heats up quickly and moves away from the basking area, thus not allowing it to spend as much time in a higher UVB outage 'zone'. This is especially true with spotlight type UVB bulbs, which may kick out more UVB but cover a far smaller area of the cage...Though Tube UVB bulbs only really produce between 5-10 units of UVB compared to the 20-250 units (sorry can't remember the name of the typical unit UVB is rated in...just know its a odd 'u' like symbol) depending on time of day, elevation and how close one is to the equator. Tube UVB lights have the advantage, if they are as long or nearly so, of the entire cage length, to spread UVB throughout the cage, instead of centered in one corner.

Basking areas that are very wide and angled, or stepped in design (or stacked like the Reese's stacks used by some reptile keepers) have the advantage of providing areas reaching a higher basking temp (say 120's F) and lower areas with temps ranging anywhere between 95-110F which still are spacious enough to allow a dragon to bask comfortably. Nor is it good to have basking areas really close to a heat or UVB bulb, this can risk contact between the dragon and the bulb, or put the dragon into a higher UVB Index zone which can be damaging to them. Mercury vapor bulbs do have a high UVB index within a certain distance..hence why it is recommend they be at a minimum distance or greater from the basking spot. Compact uvb bulbs also have a high light intensity which can be damaging to the eyes if dragons are too close to them. Certain brands of UVB (most of which are just no longer on the market or the manufacturers supposedly have changed to make them less a danger) can produce very high UV Index levels even at suggested manufacturer minimum distances.

Then there is the simple fact there still isn't alot known about how reptiles utilize UVB and just how much any given species requires to perform normal body functions. There is some thought that reptiles can 'shut off' production of vitamin D3 once they have produced sufficient levels needed for daily calcium processing. Changes in pigment or chemistry in the layers of skin/scales end up blocking most UVB thus allowing the animal to still move about during the day to maintain body temperature while reducing any damaging effects of over exposure to UVB. Or they instinctively seek sheltered areas where UVB is reduced (ie shaded areas).

Another fact is each dragon is an individual and their individual needs may vary. Even if a hotter basking spot is provided, it doesn't mean a dragon will use it, but it is good to have the option.

In my personal observation of dragon behavior, I find they take advantage of a hotter basking area first thing in the morning and right after eating. All other times they seem to bask in cooler areas (ranging between 100-110F) instead of a hotter 120 F basking spot. Thus, it may not even be necessary to have a hotter basking spot, I just feel it is good to provide one around 120F (but not necessarily 130F or more, at least not for bearded dragons).

In captivity having slightly lower top basking temperatures would require the dragon to bask longer to reach internal temperatures they need, but it does ensure they are also exposed to the highest possible UVB levels longer. As not many bulbs produce more than 75units of UVB compared to what can be pushed by the sun on a hot day, even before noon, I don't feel there is much risk of over exposure to UVB in a captive indoor setting. However there is risk of exposing dragons to too high of a UV index, if they are allowed to get too close to the higher UVB output of MVB's.

I will also like to point out that dragons can thrive in many different variations of environment. There are far more experienced keepers and breeders of bearded dragons on this forum than I am...many who do have variations in their husbandry practices. Some use hot basking temps with a good range of basking areas allowing access to various temps ranging from 95F to as hot as 125F, others stick to the 100-110F range only, with some cooler areas in the basking end of the cage. But what most always have, is a temperature gradient both in and outside the 'basking zone' or just simply the hot end of the cage.

As the majority of our readers and posters here are from North America...it is very difficult for any of us to say how dragon behave in their natural habitat....we just don't have the opportunity to observe them in the wild. What I do know about 'wild' bearded dragons, especially the 'Inland' bearded dragon which most of our pet dragons descended from, they come from a wide area in Australia, most a mix of arid and forested areas...which indicates they can thrive in both semi arid to light forested areas..which would have a wide range of temperatures. Thus they are rather adoptable to environments that cover the range of their natural habitats, so there is no 'one true method' in caring for dragons. They can thrive and remain healthy and longed lived in various conditions.

This being said, there are minimums that need to be met...Temperatures in the basking area do need to be at least 95F, with ambient temps around 80-90F, and a cool end around 75F. UVB light is needed, or if not provided, exposure to unfiltered sunlight for 15-30 min a day, or about 5 hours a week. (spread out over a few days of course). Or supplemental D3 provided (though I don't recommend a totally zero exposure to UVB method as UVB has other benefits besides allowing the body to produce Vitamin D3).

So in an effort to stop a whole bunch of pointless 'my way is better than your way' or 'my way is the best way and your way isn't' back and forth squabbling, give your individual preferences in how bearded dragons should be kept.... whether or not somebody else posts their different version. The important thing to explain is there is no one way to raise healthy and thriving dragons.

To best help newbies into the hobby, is to get their husbandry up to the best 'average' of care. From there they can tweak as needed for their dragon's needs. If basking temps are within an acceptable range (ie 95-115F) with decent UVB exposure (8.0 or better tube light) with temperature gradient so the dragon can move out of the hot end at will...then that is best. If the particular poster is not getting a healthy dragon under the 'average' conditions, then tweaking the basking site to 120F etc. may work to bring that particular dragon into a healthy thriving stat.

Keep in mind Inland Bearded dragons have a wide range in Australia...some specimens may hail from cooler or hotter regions and thus may need different husbandry conditions compared to others.

Sorry for the long post...but felt this needed to be laid out.
-----
PHLdyPayne

"In my personal observation of dragon behavior, I find they take advantage of a hotter basking area first thing in the morning and right after eating. All other times they seem to bask in cooler areas (ranging between 100-110F) instead of a hotter 120 F basking spot. Thus, it may not even be necessary to have a hotter basking spot, I just feel it is good to provide one around 120F (but not necessarily 130F or more, at least not for bearded dragons)."

Some of my scaled buddies are very attentive to their circadian rythyms...they get a couple minutes of heat in before the lights turn off : )

My dragons seem to 'retire' for the night a good hour before lights out...but this doesn't happen every night. Many times my dragon just falls asleep where ever they happen to be when lights go out. Even if its on the basking spot or in a 'hide'.

Its hard to know what dragons are doing all day, when we have work etc forcing us from observing their behaviors. A vid cam recording the dragon's activities every day would bring alot of info...but not many people have that sort of thing set up, saving the vid file and then taking the time to go through it to observe what their dragon did all day.
-----
PHLdyPayne

The proper conditions in captivity should be an average of outdoor conditions. When the sun comes up basking temps are about the same as ambient and UVB is low. At noon the basking temps. are much higher, but by then dragons have found cooler conditions. In the afternoon the temps. and UV decrease and the dragons are out again. This is all variable based on the weather of the day and the time of year. Venting is unlimited.

In captivity, the lights come on and the enclosure heats up and stays hot until the lights go out, UV remains the same. Venting is limited by enclosure design. Like I said captivity is never like the wild and no one is able to adequately reproduce it. So we go with an average. A good average basking sopot temp. that allows them to digest their food etc. is 105ish. UVB should not be at levels found outside at noon but and average of what they would receive during the time of day they would normally bask. This is why the low levels of UVB put out by today's bulbs work without harm if used as the manufacturer intended.

Newbies like to think if 105 is good them 110, 120, 130 must be better. If being 18" from the UVB is good then 8" from it must be better too. There is a such thing as too much of a good thing.

Has more to do with many hours of trial, reading, and observation and less to do with a "more is better" mentality.

You have had it perfected since day one though.

Hence... BD Master

I agree with you PHlydPayne... it is situational and dependent on individual dragons in many cases.

They have individual preferences... some enjoy hotter weather some like it slightly cooler. They are able to adapt and thrive within reason.

gradient is the key

I've spent YEARS not hours of trial, reading, and observation. That's the difference between you and me.

Years... in vain.

You're a one stop shopping BS gourmet.

Here is the article he wrote pull it up though because it has pics:

Current recommendations on UV-supply of reptiles

Author: Ingo Diegel, Moellenkotter Str. 3g, 58332 Schwelm, Germany
www.tierarzt-schwelm.de email: praxis@tierarzt-schwelm.de

For the bone metabolism of reptiles the supply of vitamins, trace elements, calcium but also UV-light (vitamin D meta¬bolism) is enormously important!
Many UV lamps give terrifying little UVB rays - or they just do not reach the animals sun place over the distance. Rickets in the young and osteomalacia (bone softening) in adult reptiles might occur.
The adequate UV illumination of the terrarium has been a big challenge for many decades to the reptile keeper. Long time, almost no light with sufficient capacity was available in stores... in contrast with the almost legendary Osram Ultravitalux 300W a real "UV-bullet" that could be applied only temporarily and with sufficient safety margin to avoid radiation damage.
Times have changed. Meanwhile, trade offers a wide selection of lamps and nearly every manufacturer in his praises as the best. Unfortunately, there are many models that give too little or no UVB spectrum, and others that can cause burns and eye damage in animals due to excessive radiation (or incorrect radiation quality (eg, UVC)).
Even for the experienced reptile keeper, it is difficult to find the right lamp without special instruments in the apparently endless supply of reptiles stores and online shops - especially as the manufacturer's instructions on the packages are often confusing and sometimes even wrong. Accurate information on the range of the emitted radiation are usually absent.
But this one is decisive for the life of our animals. With too large distance even the performance of the best UV-lamp falls flat itself, and too short distance can lead to life threatening burns.
The professional evaluation of lamps, newly developed or modified by the manufacturer, must be made by spectral analysis. Nevertheless, a handy UV-meter, like the solarmeter 6.5 by the company Solartech, which can be purchased at a relatively affordable price (compared to spectrometers) even by private owners, is a very useful tool for monitoring of UV lamps.
We have progressed own light measurements of the most common models (available in germany) and want to help with our results, to provide better UV rediation in terrariums.
The complete results of the study are based on the know-how of the Welsh vet Frances Baines that deals extensively with the assessment of UV lamps for years and receive global recognition of reptile keepers and veterinarians.
Reference measurements of sunlight on the Earth show that UVB rays in sun quality are characterized due to certain UV-Index values ("UVI".
In nature, UV index values from 0 to over 10 are measured by the solarmeter 6.5 (Ferguson et al 2009).
Definition of UV Index (Wikipedia.de 2010):
"The UV Index (UVI) indicates the sunburn solar irradiance and varies with the cloud cover, with the sunset, with the thickness of the ozone layer. It determines the necessary sun protection factor considering the irradiation time and the skin color (skin type and pre quinsy). In the predictions for that day the expected maximum value is given. In the German area in the months from May to August at noon the UV index is usually at 5 to 8. At 10a.m. and 4p.m., the values are typically about half as big. "

Solarmeter 6.5 (UV-Index)
This definition refers to human skin and a light which is similar with the sunlight spectrum and is therefore not directly transferable to reptiles and lamps with artificial UV spectra. But there are big differences in skin type. Chameleon skin, for example, substantially more UV-sensitive than the skin of bearded dragons and tortoises.
Nevertheless parallels in the classification of UV-indices are drawn. While applicable to humans UVI values up to 5 count as relatively harmless, values between 6 to 10 are to be classified as potentially and values over 11 as extremely dangerous to sunburns.
The author assumes that mainly the eyes and skin of more sensitive reptiles (various chameleons and phelsumas) are very similar to human skin and eyes and has repeatedly observed skin burns and eye damage in similar circumstances (e.g. UVI > 10).
Ferguson et al (2009) studied wild reptiles in their natural habitat and found that even the traditional "sun-baskers" avoid the extreme midday sun.
Ferguson recommends husbandry in an enclosure large enough to generate a UVB gradient. The animals can choose their place in the sun and the duration of sun exposure, and find themselves at any time in shady places - depending on the need for vitamin D synthesis.
As guidelines for the UVI levels in the vivarium Ferguson proposes the following classification (the "Ferguson zones" refer to the observations of the behavior of wild animals):

Zone 1: crepuscular or shade - UVI 0.7
Zone 2: partial sun or occasional sunbathing - UVI 1.0
Zone 3: partial to full sun - UVI 2.6
Zone 4: mid day baskers - UVI 3.5 and more

Animals in Zones 1 and 2 can be supplied with UV tubes or UV compact lamps.
For Zone 3 and 4, metal halide and mixed light bulbs are recommended.
The metal halide lamps, however, should be given the preference because of their excellent light output.
Natural UVI reference values can be useful in captivity for the positioning of the UV lamp. Depending on the original habitat of the captive reptile UVIs of about 1-4 should be available, since extreme values over 6 are only rarely and briefly used by wild animals (Ferguson et al 2009).

Lamp recommendations
Based on our measurements, the following bulbs are recommended to solar-like UVB radiation for reptiles. But be careful: if you buy at the store a number of lamps packaged and labeled exactly the same, there may be variations of performance from more than 100%! These inaccuracies are hardly avoidable by the manufacturing process, and occur even in the best of lights. The variations of the lamps are reflected in the sometimes enormous differences in the distance shown in the following recommendations.
For this reason the author recommends the purchase of a Solarmeter 6.5 to private reptile keepers for detailed measurements of the individual's own used lamps, as a valuable tool for distance determination and control of performance of UV lamps, which were previously assessed spectrometrically and found to be good.
The distance values refer to the main beam, which is the brightest spot on a sheet of paper lying under the cone of light (very important for the installation of tree branches and other solar place structures). Outside the main beam, the animals can be up to half the distance closer.

The illustration on the right examplary represents the distribution of the UV rays of a lamp, and is far away from a conical linear spread.
In the center of the beam the animals are, for example, at a distance of 20cm a much higher "UVB exposure" suspended, as only about 10cm next to ...
It would like the animal itself can decide whether it can sunbathe and take UV-light or whether it is just warms up itself, it is important to install an additional heat lamp (eg, reflector lamp).
Light, heat and radiation intensity must be individually adapted to each terrarium size and well kept animal.

Zone 1: crepuscular or shade - UVI 0.7
Bright Sun UV Jungle 50W (Lucky Reptile): about 25-40cm *
Bright Sun UV Jungle 70W (Lucky Reptile): about 35cm
Raptor Solar UV Lamp 35W (Solar Raptor): about 40cm
D3 Reptile Lamp 15W 6% UVB (CRT) (Arcadia): about 25-30cm
ReptiSun 10.0 UVB 15W (tube) (ZooMed): about 45cm
Reptistar T8 15W (tube) (Sylvania): about 25-30cm

Zone 2: partial sun or occasional sunbathing - UVI 1.0
Bright Sun UV Jungle 50W (Lucky Reptile): about 20-35cm
Bright Sun UV Jungle 70W (Lucky Reptile): about 30cm
Bright Sun UV Desert 70W (Lucky Reptile): about 35-55cm
D3 Reptile Lamp 15W 6% UVB (CRT) (Arcadia): about 20-25cm
D3 Reptile Lamp 12% UVB 15W (tube) (Arcadia): about 45-50cm
D3 Compact Reptile Lamp, 26W (compact lamp) (Arcadia): about 35-40cm
Compact D3 Reptile Lamp, 26W (compact lamp) (Arcadia): about 35cm
Compact UVB Sun, 15W (compact lamp) (Lucky Reptile): about 35-40cm
Compact UVB Sun, 23W (compact lamp) (Lucky Reptile): about 35cm

Zone 3: partial to full sun - UVI 2.6
Bright Sun Desert 70W Flood (Lucky Reptile): about 40-55cm
Bright Sun Desert 70W (Lucky Reptile): about 25-50cm *
Bright Sun Desert 50W (Lucky Reptile): about 40-55cm *
Raptor Solar UV Lamp 70W (Solar Raptor): about 55cm
SolarGlo 125W (Exoterra) about 30-80cm *
SolarGlo 160W (Exoterra) about 40-60cm *

Zone 4: mid day baskers - UVI 3.5 and more
Bright Sun Desert 70W Flood (Lucky Reptile): about 35-50cm *
Bright Sun Desert 70W (Lucky Reptile): about 20-45cm *
Bright Sun Desert 50W (Lucky Reptile): about 30-50cm *
Raptor Solar UV Lamp 70W (Solar Raptor): about 40-50cm
SolarGlo 125W (Exoterra) about 20-80cm *
SolarGlo 160W (Exoterra) about 20-50cm *

Tubes and compact lamps need an effective reflector to achieve the measured values!
Basically because of the excellent light output metal halide lamps should be preferred.
*) The extreme differences of the individually measured lamps keep dangers that permit no general recommendations - they can only be objectified by measurements!

Supplement
UV filter: Normal window or vivarium glass is impermeable to UVB light. Therefore, the lamp must be either inside the terrarium (not reachable for the animal) or above the terrarium (eg, reflector cone standing above the metal gauze). Note, however, that for example the metal gauze attenuates UV radiation on their way to the animal by about 30-35%.
Therefore a general installation instructions for UV lamps is not possible!
The measurement of the actually achieved UVI values in individual terraria is the only reliable way to capture the animal incoming UV radiation.
Excursus: Comparison Solarmeter 6.5 vs. Solarmeter 6.2:
For several years the solar meter is 6.2 (Solartech) is increasingly being used in the terrarium. It measures UVB levels in the unit μW/cm2. During the measurement of nature (under the "real sun" with the values of about 100μW/cm2 by solar meter 6.2, the solar meter 6.5 shows UVI values of about 1.6 - 2 at the same place.
The following graph of the spectral sensitivity of both instruments, however, shows that the solar meter 6.2 (blue line) also still collects radiation within the UVA range (> 320nm), while the solar meter 6.5 (red line) clings very close to the vitamin D synthesis curve (black line).
The vitamin D synthesis undergoes its maximum at about 297nm. Harmful UVC radiation starts below 280nm.

The solarmeter 6.2 therefore can be deceived by elevated UVA radiation. Now, if a lamp actually beams too little UVB radiation in the relevant range of about 290-310nm, but very much UVA radiation (> 320nm), then the reference values of 100μW/cm2 might be reached, although the lamp is not suitable as UVB light.
Therefore the solarmeter 6.2 should no longer be used to compare different bulbs, but the SM6.5 be given priority if we are to judge whether a lamp is appropriate for vitamin D transformation or whether a material is transparent in the vitamin D effective wavelength range. The assessment of whether there is also a higher risk of burns, must be left to the spectral analysis.

Annex
Important: If purchasing the solar meter please pay attention on the sensor! Order the meter with Siliconcarbid sensor (SiC), which is suitable for the measurement of UV lamps - the standard sensor can be used for the measurement of natural sunlight only!

Literature
BAINES, FRANCES, 2009: personal communication
Frances Baines is a vet and author of the website www.uvguide.co.uk.
FERGUSON ET AL. 2009: Voluntary Exposure of Some Western Hemisphere Snake and Lizard Species to Ultraviolet-B Radiation in the Field: How Much Should a Ultraviolet-B Lizard or Snake in Captivity Receive? Zoo Biology 28: 1-18
LINDGREN ET AL. 2008: Measuring Effective Vitamin D3-Producing Ultra Violet Radiation B Using Solar Tech Solar Meter 6.4 handheld UVB radiometer. Bull Chicago Herp. Soc. 43 (4) :57-62, 2008
Many thanks to Frances Baines and Sarina Wunderlich for their patience in answering all questions and improving and rounding out the script!

If you look at what he recommends...

Zone 4: mid day baskers - UVI 3.5 and more

20 centimeters for zone 4

which in turn equates to 7.9 inches

My exo terra bulb 125 watt is exactly 8 inches from dead center to the bottom where the substrate begins.

I measured it, and could take a pic.

6 inches from the bulb is where I take the measurements from roughly.

Actually closer because the solarmeter 6.2 is more than 2 inches from top to bottom.

I would never put my dragons at risk without reading on this first. I have belonged to the group for awhile and that is the reason I bought the 6.2

Additionally...

I use boxes as hides as they are easily replaced and... hallowed out logs bought and sold in stores.

The dragons need a gradient between both high intense uv and near to zero.

This is optimal.

To do this you need a decent sized enclosure.
Adults 4 feet long or more.

My dragons do not sit directly under the light for hours. Normally they are off to the side or in many different areas of the enclosure. Being forced to sit directly under the bulb and there would be issues. Surface temp is 126-127 directly down.

The other bulb is a reptisun 10.0 in their enclosure and it emits 20-30 uW/cm2 which is minimal uv and zero uv in the hides.

I have two other MV bulbs and have similar setups with those also. One hangs from an overhead device with a shroud. I have tested and played with these setups for hours.

Using a reptisun 10.0 18 inch bulb, a uva, and a mercury vapor on my zone 4 side.

They key to housing dragons is gradient.

Allow them enough room to self regulate as they are opportunistic sun worshipers. Clouds and the spinning of the earth provide a great amount of variation in the natural world. It has been talked about and some feel it is a good practice to rotate reptiles into new enclosures with different light setups after several months in one enclosure.

Do so...
after a thorough decontamination.

By doing so they get some variation in light and living conditions and gives them variety as found in nature.

Also you need to conduct a cool down and taper off the radiation intensity phase for brumation.

In nature dragons will cool down. When they do so it just so happens that there are not as many bugs outside in Australia.

The combination of less heat and less bugs is a cool down phase.

Gives their digestive systems a chance to rest also.

enjoy

Wait? But you don't have a 6.5 so you cannot measure UVI. You only have a 6.2 remember? It measures UVB. I have a 6.5 but I don't have your bulb to measure the UVI on.