From my experience additional UVB works great. I'm using 2 Agromax 2ft. bulbs for my bloom area and Arcadia reptile bulbs with 12% UVB for my little veg area. It makes sense to harden them up against UVB so they get used to it from the beginning. To use it only for the last few weeks can cause some serious issues especially when you use the more powerful Agromax or Solacure bulbs. The hardening process takes around a week. Imagine you want to put a houseplant outside in full sunlight. She will need a shady spot at the beginning until she gets used to the sun's UVA/UVB radiation. With UVB its almost the same.
Reptile bulbs can be used all day long together with the mainlight. I'm using the last veg week to harden the plants up and start with 2+2h UVB treatment. From bloom week 3 or 4 (when the plants start to show the first trichomes) I start to increase it slowly untill they get the full 12h for the last two weeks.
Agromax and Solacure are 5 times stronger and their light extends a little deeper into the UVB range. Reptile bulbs have also only very little UVB output below 300nm, Agromax and Solucure spectrum goes down to 280nm. For this reason a reptile bulb needs much more time to trigger the UVR8 receptor. The lower the wavelength the more energy a photon transports. That means a 280nm photon has much more energy than a 300nm photon. For this reason it is impossible to use these bulbs for 12 hours without getting heat stress. You also need twice as much distance and you should split the 1-2 hours UVB treatment to 4x 15-30 minutes to avoid heatstress and wilting leaves.
The test results below are with and without UVB and show a significant improvement in thc content. Plants getting UVB are also more colorful especially purple strains look more beautiful. The terpene profile will also change and a plant getting UVA/B smells different like the same plant getting no UVA/B.
I like the Solacure bulbs because of their built in reflectors but the old T12 standard is outdated and siutable balast are rare.
The Agromax bulbs use the latest T5 standard and siutable ballasts are widely available. You can also use dimmable T5 ballasts which is a huge benefit because each strain tolerates a different amount of UVB light.
I have currently 5 mostly sativas in my little cab, 3 of them tolerate less UVB and already show heat stress while the other two have no problems. Distance is 16-20" and bulbs are on 3 times the day for 25 minutes. Most of the damage occurred when I tried to give them 2x 2h around day 30. Since then I've reduced it to 3 times 25 minutes and hardly any new damage has occurred till now. Currently its day 47 and I expect another 3-5 weeks.
This is an Amnesia x BlueDream cross(F1) and you can see upwards curled fan leaves. She has nice white and orange pistels from the beginning.
This one is a BlueDream and she is at least 4-6" higher compared to the AxBD cross above.
No heat stress, no curled leaves... she looks like she needs another 5 weeks.
