Hi,
Dont know if this well help, but halfway down this page
https://www.thetortoisetable.org.uk/tor ... r-housing/ is a section on lighting and heating, and here's a definitive article from the Tortoise Trust -- it might be long and rather complicated but should provide lots of information:
https://www.tortoisetrust.org/articles/lighting.html
I think most people use the mercury vapour combined heat/light/uvb bulbs, as you do and they are good. Just a quick question because 125W seems a bit powerful for an indoor table in summer -- out of curiosity, what temperature are you getting at floor level on a warm day, directly under the lamp, and how high is the lamp above the table? Because you need to frequently raise and lower the heat source in order to raise and lower the temperature in the table, that means that you are also increasing and decreasing the distance of the UVB source, and for that reason I prefer to have mine separate.
So I use a variety of reptile basking bulbs as the source for heat and light (I use a higher wattage in cool weather and a lower one in warm weather), and then a flourescent UVB tube for the UVB. There are various studies on which are the best bulbs, and I can't remember now, but you are aiming for brightness and a good spectrum. They come in halogen, incandescent and spot and flood lights, and I've tried all of them, but can't really remember which ones impressed me more. I think you would be fine with any of them. Don't get the infra-red or any other red light bulb.
I also find that it's best to get the longest UVB fluorescent tube that will fit over your table (my table is 7' long so I use a 4' tube), and in that way the tortoise will be exposed to UVB almost everywhere he is in the table. The best tubes are the T5 range, and should say either 10% or 12% on the box. Those are the highest grade. There are also compact UVB fluorescent tubes, but there have been various health concerns with them, and I think I would stick with the straight, long tubes.
With the fluorescent tube you also need a starter unit, something to hang it from, and a clip-on reflector that protects your eyes from UVB and also directs more rays down into the table. Something like this:
https://www.reptiles.swelluk.com/arcadi ... 4w-t5-tube It just clips on to the tube itself (UVB tubes produce almost no heat, so it's safe to clip the reflector onto it).
I have used a thermostat in the past, but don't use one now -- I just have my lights plugged into ordinary timers that are set to go on and off in the morning and evening. I think that with an ordinary thermostat, if it gets too hot, then it will just turn the bulb off, and with the sort of bulb you have that would also cut off the light and UVB. So I just go with timers and raise and lower the bulbs a bit as needed.
However, thermostats can be really useful, especially if you are out a lot during the day. The best thermostats, I think, are the Habistat range. I used to use a dimming Habistat -- something like this:
https://www.reptiles.swelluk.com/habist ... 600w-white and that worked pretty well. Be aware though that you can't use a dimming thermostat on the combined bulb that you currently have -- for that you would need an ordinary thermostat that just turns on and off. You could use a dimming thermostat on any other bulb that produces just heat and light, and also on the fluorescent tubes. I use this sort, but there are better ones:
https://www.reptiles.swelluk.com/habist ... 600w-white
Sorry, I've gone on far too long. Do come back with any more questions, and I hope that some of the information here is helpful.
Nina
