Lighting & Temperature

The Set-Up
UVB Lighting
The most important part of a dragon's enclosure is not a fancy food dish, a pretty flower or a cool basking platform, it's their UVB light. Without this light the dragon cannot absorb calcium and process other vitamins. It will become horribly disfigured and in most cases die due to Metabolic Bone Disease. These lights give a dragon they ability to break down their food and vitamins like the sun does for them in the wild. The best kind of UVB lighting is TUBE lighting. You need a 10.0 Desert Reptile bulb which are long, round tubes. Lighting should be no closer than 12 inches due to the UV output could hurt a dragon's eyes, but it should not be farther away than 18 inches or it will not reach the dragon. UVB should be kept turned on from 10-12 hours a day, every day. Using reflectors can also help more UVB reach your dragon.
Tip: UVB lighting needs to be replaced every 6 months in average, the UVB output will not last forever. Heat basking bulbs can be replaced just as they blow out, normally they last a year as long as they are not moved too often.
Night Heat Source
Picture
If you are housing your dragon somewhere in your home where the ambient temperature drops below 60F at night you need a night heat source. The best choice for this is a ceramic heat bulb. They emit no light just heat and won't disturb your dragon's sleep pattern, and they fit right into most light fixtures.
Bad Lighting Choices
NEVER USE: Coil or Compact UVB bulbs. These bulbs are most often used for tropical reptiles/amphibians with small and generally tall cages. They emit a more centralized UVB light, and as dragons require longer and lower cages these are not the ideal UVB lights for having UVB across an entire enclosure. Also they are hazardous to dragons eyes with a history of causing causing infections and eye issues, including blindness. Please do not ever use these lights for a dragon.
NEVER USE: Colored night heat bulbs, or any night at light. Bearded Dragons are Diurnal meaning they are active during the day and not active at night. When it is dark it is their instinct is to sleep just like you. These colored lights are meant for nocturnal reptiles and this light at night interrupts the dragons sleep pattern making them angry and unhealthy. Also dragons see color so using these colored lights as your basking lamp covers their enclosure in one color causing your dragon to be very confused, aggressive, agitated and can decrease their appetite.
Its Getting Hot in Here
Despite what people think bearded dragons are not desert lizards out roaming the sand dunes, they are more central and live in areas with brush, rocks and even pooling water. They need both heat and mild humidity in their enclosures to aid in shedding skin. Dragons need one side of their cage to be the 'hot side' for basking and one side to be the 'cool side' for cooling off. A heat basking lamp is needed on the 'hot side' of the cage for warmth and the temperature should range from 95-105F for adults. For hatchlings we suggest not allowing the temperature to go over 100F. And for the 'cool side' of the cage we suggest 80-85F for both adults and hatchlings. Nighttime Temperature should not drop below 60F. Proper heat ensures a dragon's ability to digest its food and stimulate blood flow. Make sure to stay in these safe ranges, you don't want to overheat your dragon or keep it too cool and make him/her susceptible to respiratory infections and digestive issues.  I keep our heat lights on for 8-10 hours in the fall/winter and 2-6 in the spring/summer, but I live in California. You have to figure out what works best for the climate you live in. Heat light watt amounts vary on your enclosure size, you will have to try different ones until you get the right balance of heat vs. cool.
Bad Heating Choices
There is such a thing as too hot when it comes to dragons. I strongly discourage the use of heat rocks and heat pads for any reptile not just dragons. They are notorious for causing burns as their temperatures can be very erratic. Also if a baby dragon falls into a deep sleep on top of one it could literally cook them if it got too hot and they were too tired to move. They also can super heat parts of cages and cause melting decorations and cracking glass.
Natural Sunlight

Keep in mind taking your dragon outdoors for natural light is great, but in no way will function as enough UVB for them. They need a minimum of 10 hours of sunning a day, every single day. I have seen dragon owners that keep their dragon's cage by a window and have sunlight shine in and they think they don't need to have a UVB bulb, this in incorrect. UVB gets broken down through glass of the window and the glass of the cage. Your dragon's life depends on their UVB bulb.
Know Your Stats
I can't stress enough how important it is to know the temperatures in your enclosure. The humidity of a dragon's enclosure is also important and could stay around 30-35 on a constant basis. The easiest way to monitor stats is a digital combo meter like the one below or a needle gauge meter. They are more accurate than the stick on strips, and they last longer too.
Get Automated
Timers are an easy way to set up your dragon's heat and UVB lighting. Simple timers are easy to use and can be found at any hardware or home improvement store. Timers are the best way to ensure your dragon gets the right amount of light and heat even if you aren't home to turn it off and on. You can buy ones at pet stores, but keep in mind you are paying more for them because they say they are for reptiles, the ones at home improvement stores do the exact same thing for less cost to you.