UV burn on plants?

[Tom]

Hmm, the 6.5 is what they also used in that article i linked
http://www.uvguide.co.uk/phototherapyphosphor-tests.htm
which says they got an index of 2.3 off the Reptisun 5.0. I don't see that they specify at which distance that is, but it does say "recorded with the UV Index Meter at the distance at which the Solarmeter 6.2 reads exactly 100 µW/cm² of total UVB." My little brain is getting overloaded.
But the gist of that page is that these bulbs do put out wildly excessive amounts of UV in the narrower band of UV that is specifically needed by our tortoises. Measured with the same meter you have.
Of course the article is 8 years old and the bulbs may have been modified since.

And i do have an aluminum reflector, and my mint plants have responded as if they were getting fried.

All I can tell you is what I got from my bulbs, and a few other people's bulbs with my meters at a given distance. Distance matters tremendously in this case. Even one inch difference gets vastly different results. I can get 2.3 off of a Reptisun 5.0 if I put the meter close enough.

 

[jaizei]

For more comparison, I have a 4-5 year old MVB that gives me readings of 7.1 from 12" and through a screen.

What does the 6.2 show when you're getting 7.1 on the 6.5 @ 12"?

 

[Tom]

216.

 

[Loohan]

The mint leaves did turn white, or greenish-white. I then put the pot in a sun room for weeks, and the stalks lenghtened and new, green leaves came out.
Meanwhile, i had switched to my spare bulb of the same brand and type. And also was growing the pothos in the tote with no problems. I returned the revitalized mint plant to the tote. I have had no further problems with leaf burn.
I conclude that the first bulb puts out way too much UV.

 

[Loohan]

Aargh! 2 days after posting that, and now the mint is turning whitish again in the same way!
But the pothos now also in there seems unaffected, even though closer to the light.
So maybe it is just something weird about mint. I have grown this mint for 20 years, in full sun in TX, in full sun and shade in AR, and never seen it do this outside.