100w is plenty and you would never really need more than that unless you have something like a 7 foot viv. There isn't really a best one its just what one suits your viv the best if you have a little viv a 40w spot bulb would be enough. You need a basking temp of around 105f-110f and a cool end of 80f-85f so just get the one thats best suited to you.

If your bulb has a high enough basking temp but isn't heating up the viv enough get a bigger bulb put it higher off the ground.

I dont know why it would make a 40w bulb turn on but if its only 40w it would probably be ok to plug in with out a stat untill morning

 

40 watt should be fine thats what mine are on just move the probe for the dimmer closer to get the temps up

 

As long as the 100w gets the temps right stick to it. have no idea why the 40w bulb doesnt work if the stat is working with a 100w bulb.

 

I always have a good supply of spare lightbulbs just incase they do blow as you never can tell how long they will last, i got my last lot from Lightbulbs direct
Light bulbs, halogen lamps, spot lights and tubes by mail order in the UK

Really cheap and i got 10 so i wont have the probleof running out any time soon, they do the reflector bulbs which i think are just as good as any of the reptile branded ones, gets my temps just right.:no1:

 

i belive it has something to do with the amps running through the system on the dimmers the habistats do say 40 watts shouldnt be used with them.

 

bugger i must be getting old lol mine are on a 60 watt:blush: