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The Exo Terra Solar Glo is, as advertised, a sun simulating bulb. Also known as mercury vapour bulbs (MVB), these not only emit light and heat but also UVB rays. These are essential for reptiles, and this type of bulb is one of the closest things to the actual sun you can provide for your captive herps.
These are really the budget MVB of the reptile world; they function well when they work, but are of a lesser quality than some of the other brands, and they don't last as long in terms of general wear and tear or UVB output. I have found it very difficult to get an answer as to when these bulbs should be replaced due to diminishing UVB levels, but as it happens it's not been something I have needed to worry about yet (more on why later). But it is worth noting that even when the UVB has 'run out' they will still illuminate and appear to be working, so you must keep a note of when you started using it to ensure you are always providing the necessary UVB. I know of people who use these for plant growth/in greenhouses once they replace them, as they still put out a lot of light and heat when the UVB is done.
These bulbs need to be suspended so they hang straight down, having them mounted at an angle, such as with a clamp on lamp holder, can cause flickering and shorten the life span. Also, they need large holders as they require a lot of cooling air flow around the bulb; if this is restricted the bulb will overheat an cut out. Overheating and cutting out further shortens the life span, and once one of these bulbs has been switched off it must be left for around 1.5 hours before turning it on again - this is to allow the filament to cool down fully. These bulbs are not suitable for use with thermostats of any kind for this reason, but can be used with a simple on/off timer to regulate the photoperiod.
Possibly the biggest advantage (other than UVB quality) of these bulbs over separate UVB / heat sources, is that they are neat. You only need one holder (albeit the huge ones) and one socket. This is a huge advantage for those of us who have large collections and not enough sockets! The downside of this though, is that if your bulb blows you are then without heat AND UVB and you must cobble together something, for heat at least, in the meantime.
I have one of these Solar Glo bulbs on my indoor turtle pond, and it has been really good; the heat and light it kicks out are plenty sufficient, and the beam is quite wide giving good UVB coverage. The turtles in the pond love basking under it! This is the only enclosure I have a MVB on so far, and I have to say how much I appreciate the tidiness as this indoor pond is at the back of my living room - the most public room of the house (and the only one with 24 square feet of safe floor space for it). It is a talking point, certainly! So I love that I only have one bulb and fixture over it because believe it or not I am actually very house proud and like everything to be in its place.
However I have had my fair share of issues with these bulbs; the first bulb I bought only lasted three months before it blew, despite me treating and mounting it optimally. It just didn't flick on one morning with its timer. The very same thing happened with my replacement bulb, after 3 months again. So I am on my third one in seven months! If I hadn't bought it from such an excellent company I would be fuming and my rating would no doubt be lower! Many companies do not offer any guarantee/replacement for bulbs (though it does appear to be becoming more available now), as their very nature make them fragile and obviously these companies cannot control how the bulb is treated once it reaches you. I bought mine from Zooplus.co.uk for £24.99 delivered. I planned to replace after 9 months-1 year, but so far have not had to think about that, since I've had a new one every 3 months!
But, when compared to other MVBs, the Solar Glo does come off favourably in terms of price. It is literally half the online prices of other leading brands, but these are higher quality and may be guaranteed for 1 whole year (Arcadia) or known anecdotally to last up to 2 years (Megaray) before the UVB diminishes enough to need replaced, so in all honesty it is false economy. The Solar Glo is a great introduction to the world of combined bulbs and is a good choice, particularly if you need to buy a new holder for it too (the large ones can be very pricey), as it will help keep the overall cost down.
I would recommend these to others if they were looking for the best price. Don't get me wrong, when they work they are perfectly fine and do everything they should do. But in my experience they are not a hugely reliable bulb. I would recommend they be purchased from Zooplus though, as that way it's win-win with their fabulous customer service. I would recommend another brand if price was no object though, such as Megaray or Arcadia both of which I think now retail for around £40 (not including P&P).
So I'll see what happens with bulb number 3, if I can afford to I will change to a better quality brand when it needs replaced, but if not I will continue to use these, so long as I can keep buying them from Zooplus!