. What are your night temps? Reason I ask is there is quite a bit of misleading info out there, a night drop in temps is very healthy for a BD and you shouldn't need any night time heating unless its dropping to around 10c.
If you do though I would recommend neither of those options. Firstly there should be no visible light at night, whatever the colour it will disturb your dragons sleep. A heatmat can be dangerous for a BD as they don't recognise heat from below too well and if it reached a dangerous temp or generates a hotspot, albeit unlikely it could burn your dragon. They are also useless at increasing ambient air temps so would only be of use if your dragon was on top of it. For a BD night time heat should only be provided by the use of a CHE, this on low will raise the ambient temp of the viv and should always be run on a thermostat.
Hope that helps, Tom.