10. I am not familiar at all with Metal Halides. Can you elaborate more about this type of lamp. Do you perhaps have a Metal Halide Spectograph that you can share with us? -Q contributed by Kevin Zamp-
Metal halide lamps are basically mercury vapor lamps with added compounds of various metals and halogens inside the arc tube. There's a great description of these here: http://en.wikipedia.org/wiki/
The exact combination determines the color of the light produced, and it is much brighter than an ordinary mercury vapor lamp. A good quality 70W flood will produce maybe 75,000 lux at 12 inches... that's illuminance at full sunlight levels. Obviously you don't need to have the lamp so close... placed at a greater distance, the light will cover a much wider area but still provide intensely bright illumination.
The other impressive thing about metal halides is that ones with "daylight" color balance (around 5,000 - 6500K) have so many "spikes" of light at different wavelengths, produced by all the different chemicals, that the spectrum is almost continuous. This makes for extremely good color rendering - the spectrum is more like sunlight than any other lamp.
This chart shows the spectra of sunlight, one of the best metal halides, the Iwasaki/Eye Lighting Color Arc PAR36 (sold for human use) and a mercury vapor lamp for comparison.
They are all externally ballasted, because they need really precise control of their operation. And just any old ballast won't do. The quality and color of the light is extremely sensitive to the current flowing through the arc tube. High quality ballasts are needed to avoid flicker, frequent cutting-out and re-starting, and loss of the full color spectrum.
They are ignited by a 4KV initial pulse from this ballast. This requires excellent electrical connections and fixtures designed to handle that sort of voltage, as well as the heat. Anything less - moisture or dirt in the terminals, for example, or too long a cable between ballast and lamp - and the lamp may fizz and sputter, but it won't ignite properly. (They take a few minutes to ignite and reach full brightness anyway, often with assorted flashes and flickering).
The Solarmeter 6.2 is the most versatile and useful broadband meter available; I wouldn't be without one. But like all broadband meters, it can only measure what it "sees"; and it sees the whole spectrum from UVC to a short distance into the UVA. This means it can't distinguish between a lamp that produces a lot of dangerous very short wavelength UVB from one which produces a lot of harmless long wavelength UVB. In other words, you can use it to monitor a lamp's decay, but you can't use it to decide how similar a lamp's output is to sunlight, or to compare one brand of lamp with another.
The 6.5 meter gives the readout in terms of the easily understood UV Index. If we know the basking habits of our reptiles, we can estimate the UV Index they would choose to expose themselves to, in the wild, and then decide how much UVB to offer. It's a very handy safety feature, too. The highest UV Index ever seen, at mid-day on the equator at sea level, is around 16 - 17. Reptiles would rarely venture out into that. So what would you do if you discovered your new lamp would expose your reptile to UV Index 100 or more? Sadly, this is no joke...I know some "spot" mercury vapor lamps still on sale today which emit extremely dangerous levels like that, at the manufacturer's recommended basking distances..
The only drawback with the 6.5 meter is that it's measuring such tiny amounts of light that the UVB from a fairly low-UVB fluorescent tube, at basking distances, will hardly register a flickering 0.1 or 0.2 on the meter. At the very limits of its resolution, the meter is not very accurate at such low levels.
But unfortunately, the 6.5 meter not be on every herper's shopping list, today.
It relies upon a SiC sensor. These are now considered outdated, and are being replaced by AlGaN sensors in most applications. The supply is now very limited; they are no longer being manufactured, and only one supplier, with dwindling stocks, now exists. The Solarmeter 6.5 with a SiC sensor has just unavoidably suffered a massive price increase as a result, although Steve Mackin believes he will be able to supply these very special meters for some time to come.
The AlGaN sensor is suitable for monitoring sunlight and lamps with spectra very much like sunlight. However, it does not respond well to short wavelength UVB and UVC, and as a result broadband meters fitted with AlGaN sensors do not give comparable results with many types of reptile lamp, and in fact the ones I trialled were unable to detect hazardous output from several lamps giving extremely high UV Index readings with the original Solarmeter 6.5 with the SiC sensor.
12. Let's say that we allowed sunlight into our reptile room. Even though it passes glass, does it still keep a lot of the spectrum below the UVB level? -Q contributed by Kevin Zamp-
No. Ordinary glass (as opposed to quartz glass) acts like a UV filter, progressively blocking shorter wavelengths of UV. Window glass blocks 99 - 100% of the UVB. It allows some UVA through (about 65% at 350nm) and almost all visible light (over 90%).
If you want to glaze a window to let in some UVB, though, special high-transmission glass (which is very low in iron) is available which will let some UVB through. In the USA, one such glass is PPG Industries "Starphire" Uncoated Ultra-Clear Float Glass. Two brands which can be purchased in the UK are Asahi Glass Company's Planibel Clearvision (28% transmission of UVB at 305nm) and Pilkingtons' OptiWhite (25% transmission at 305nm).
13. What do you think of external vs. internal ballasted lamps for MV and MH (if it comes that way) -Q contributed by Kevin Zamp-?
From the point of view of light quality, one might think self-ballasted (SB) mercury vapours would be better than externally-ballasted (EB) ones, because of the tungsten filament producing some continuous-spectrum, golden light to offset the very "spikey" spectrum and very poor colour rendering of the light from the mercury arc. They are marginally better; but the arc tube is so bright it overpowers the tungsten filament. In my opinion both SB and EB lamps should be combined with "daylight" full-spectrum lighting, ideally with a continuous spectrum, as I mentioned before.
The main reason for choosing an SB lamp would be to increase the heat at the basking spot. A 160W SB MegaRay produces a very suitable basking spot for my chuckwallas (up to 120F!) which is quite impossible with a 60W EB MegaRay. Conversely, an EB lamp would be much more suitable for use with montane species, requiring high UVB but lower temperatures.
14. So, as regards provision of the best light for reptile keepers, do you have any more tips that you can share?
If anyone asked me to summarize everything in just a few sentences, I'd probably say:
Research your species! Plan to mimic its natural light environment as far as possible.
"Select and combine" lamps to get the best spectrum you can.
Always, always check your temperatures.
Never buy anything just because it's really cheap. UVB lamps are health products, like drugs, not fashion accessories like plastic plants or food bowls. Would you buy a packet of pills if you didn't know what was in them?
15. Last, but not least, what is next for you? Any exciting researches you are going to do? Books to publish?
Right now, I just want time to update the UV Guide UK website!..... but one day, yes, I do hope to write a book on the subject. There is a lot going on at the moment, too, that I'm very excited to be involved with. For example, Peter Nunn at Alice Springs Desert Park has completed a marvellous survey of the voluntary UVB exposure of wild long-nosed dragons over a full year; we hope to write up this study with Dr. Gary Ferguson.
Thank you so much for this wonderful opportunity! I wish you many success for your future research.
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