UV meters in terrariums: Which SOLARMETER ® is the right one – 6.2R UVB or 6.5R Index?

For many reptiles, UV light is not an ‘extra’ but an essential part of species-appropriate care. Among other things, it influences vitamin D₃ synthesis, calcium metabolism, activity and well-being. A balanced light spectrum with UV content also determines whether they can perceive their surroundings in true colours.

However, unlike for reptiles, UV radiation remains invisible to the human eye; we cannot perceive it. A simple check, such as for temperature and visible light, is therefore not possible for us. This is where UV measuring devices come into play.

Below, we compare two proven handheld measuring devices that are frequently used in terrarium keeping – the SOLARMETER® 6.5R Reptile UV Index and the SOLARMETER® 6.2R Reptile UVB – and explain which device is suitable for which purpose.

The SOLARMETER® 6.5R Reptile UV Index – Understanding UV with the UV Index

The SOLARMETER® 6.5R Reptile UV Index Meter is the best-selling UV measuring device in terrarium keeping – and for good reason.

What does the 6.5R Reptile UV Index measure?

• It detects UVA and UVB radiation.
• The measured values are not displayed directly.
• Instead, the device uses them to calculate a UV index (UVI)

This UV index matches the so-called Ferguson zones, which describe the UV conditions to which different reptile species are naturally exposed in their respective habitats.

Why is this so practical?

The UV index is:

• 
  easy to understand
• interpretable in relation to species
• ideal for evaluating sunbathing spots in the terrarium

To put it simply:
👉 I measure at the sunbathing spot – and immediately see whether my animal is sitting in ‘its’ natural UV zone there.

This makes the 6.5R ideal for:

• the initial setup of a terrarium
• the positioning of UV lamps
• the assessment of basking spots for different species

The 6.5R is the most intuitive and practical tool, especially for keepers who follow Ferguson zones.

The SOLARMETER® 6.2R Reptile UVB – Measure UVB accurately and detect lamp ageing

The SOLARMETER® 6.2R Reptile UVB Lamp Meter takes a different approach.

What does the 6.2R measure?

• It measures UVB exclusively
• The measured values are output directly as physical values (e.g. µW/cm²)

Why is this important?

UV lamps ‘age’.
This does not mean that they suddenly go out – rather, the UV-emitting light source inside is continuously consumed, reducing the UV output of the light source. The UV output decreases. .

• How quickly this UV output decreases varies greatly from luminaire to luminaire, depending on the production process.
• This process is not visible.
• Even a lamp that still shines brightly may hardly emit any UV light.

This is exactly where the 6.2R shows its strength.

The big advantage of the 6.2R

With the exact measurements, you can:

• track the UV output of a lamp over months
• objectively determine when a light source really needs to be replaced
• avoid animals being ‘apparently well lit’ but actually undersupplied with UV light

An index display is less suitable for this ongoing monitoring and documentation – what counts here is the specific numerical value.

Which device for which purpose?

Conclusion: Two devices – two useful tasks

Both solar meters pursue different but equally important goals:

• The SOLARMETER® 6.5R Reptile UV Index helps to adjust the UV supply in the terrarium in a comprehensible and species-appropriate manner.
• The SOLARMETER® 6.2R Reptile UVB ensures that this supply is maintained permanently by monitoring the actual UV output of the lamps.

Many dedicated reptile keepers therefore use both devices in combination:
👉 The 6.5R for ‘Where am I?’ – the 6.2R for ‘How much longer?’

After all, a perfectly set up living environment is of little use to the animal if the UV lamps quietly and invisibly lose their effect over time.

Also worth reading: FAQ: UV measuring devices in the terrarium