Surface Temp. Vs. Ambient Temp.

Something I've always wondered, do you read temperatures off air/ambient temperature or surface/substrate/basking temperature? 

I am getting some forest scorpions (H.petersii) and I am currently setting up their enclosure, and I can't seem to get the warm side (ambient air temperature) warmer than 26.5C (79F) however when in contact with the base of enclosure I get about 34C (93F) - that's with no substrate, so with a good few inches of coco fiber I should get a nice cosy 30-32C. 
I am using a heat mat by the way.
Was also wondering how much of a thermal gradient you have? I understand to have 1/3rd of base covered with heat mat, but what temperature would be optimal for a cool side?
Another question I have is the photo-period requirements of scorpions. My main concern is that when I am working late into the night, and I have lights on in the room will this effect the nocturnal foraging behaviour and general health of the scorps? Also vice versa, when I can't be bothered to get up in the morning and open my curtains. 

Any advice/experience/input on any of these issues will be gratefully received.

many thanks      

Usually people don't recommend using heat mats for burrowing scorpions because when they get hot, they dig down. This works in the wild, but with a heat mat they just get hotter. Try using a ceramic heat emitter or place the heat mat on the side. That creates a heat gradient that is most desirable.

I have considered using an IR bulb or a ceramic bulb but I'm not sure how to implement it in my plastic RUB set-up? Any ideas?

(Probably using the bigger RUB with more floor space)
I was also under the impression that if the environment is not favourable the scorp won't go there? i.e. won't dig any deeper if it's too hot, or start another tunnel in a cooler area.

If you can get a hold of a bendable lamp or something like it, you could just bend it or place it over the top. I use this method.

I wasn't sure if it would melt the plastic/ penetrate the plastic effectively but thanks, I shall try this.
Any advice for my other questions in OP?

There is nothing wrong is using a heatmat with scorpions, but you must place it vertically on one side, never under the enclosure. This way you get a temp gradient as well.