Well, let's see here. You need to try to set up a temperature gradient in your enclosure. Since it's a 40 gallon breeder tank, it should be possible to set some fairly distinct gradients. What kind of heat sources do you have already available? Do you just have the Solar Glo as your heat source? If so, 160 watts is relatively high, so you should change to a lower wattage, or change to a different type of
UVB bulb (mercury vapor bulbs tend to give off a lot of heat, while most of the tube type UVB bulbs give off relatively lower amounts of heat). The
UVB bulb is necessary, and therefore, if you cannot afford to buy a different bulb or a lower wattage, you
could try purchasing and using a dimmer (this will let you adjust the heat and light output);
however, the issue with this is that because the MVB is your heat
and UVB source, you will be decreasing the heat
and the UVB output, in which case, you probably do not want to affect the UVB output (unless the UVB output is too strong, than dimming it a bit could work; however, you would need a proper way of making sure it was still putting out adequate amounts of UVB). Another alternative is to utilize a lamp stand of some sort to alter the height of the MVB from the enclosure, which would alter the amount of heat being put directly into the enclosure (the room might warm up a bit, though); however, once again, this causes problems in terms of whether or not the UVB at a certain height would be adequate if changed (the amount of UVB that reaches the bearded dragon is dependent on the distance between the source and the bearded dragon).
Honestly, the best way is to invest in a new type of bulb or a lower wattage. If you are able to change to a new type of bulb, try the Reptisun 10.0 tube type bulb. It should be cheaper than an MVB (the Reptisun 10.0 can be purchased for low to mid 20s, I believe), and releases less heat. You will most likely need to get another heat source, however, but these should be relatively cheap, as you can use common household light bulbs as a heat source in association with the tube type bulb, if necessary. You may have to invest in a specific light fixture for the light bulbs, but it shouldn't be too expensive, and the bulbs themselves are very cheap and come in a number of different wattages, making it easy to switch if you need more or less heat; in fact, just today, I changed my 60 watt bulbs to 40 watt bulbs to deal with the temperature change associated with the new spring season.
Some other ways, though not quite as accurate or reliable, could be to increase air condition within the room, and/or opening windows, if the temperature outside is cooler than it is inside. However, you will have to carefully monitor your bearded dragon's enclosure's temperatures, as these methods of decreasing the heat inside the room are relatively difficult to maintain.
Other than that, unfortunately, I can't really think of any other alternatives. Whatever you decide to do, just remember that a
UVB bulb is necessary, and that you need a cool side, a warm side, and a basking spot/area within the warm side (for specific temperatures, see my first post).