We sell Mega-Ray mercury vapor UVB bulbs, so treat this page as what it is: a retailer’s summary of other people’s measurements. Every figure below is linked to its primary source, and the last section lists what the data does not support — including several claims that used to appear on this site and have been removed.
There are three independent sources of test data on Mega-Ray lamps. All three are the work of Frances Baines MA VetMB MRCVS, the reptile-lighting researcher behind UV Guide UK and the lead author of the BIAZA UV-Tool.
The measurements, at a glance
| Measurement | Result | Source |
|---|---|---|
| UVB lost after 12 months, self-ballasted lamp | ≈15% (280 → 240 µW/cm² at 12″) | Baines, 2006 |
| UVB lost after 18 months, same lamp | ≈17% (233 µW/cm² at 12″) | Baines, 2006 |
| Burn-in loss, first 90–105 hours (7 lamps) | 3.5% average, range 0.6–5.7% | Baines, 2006 |
| Change at 105 hours, current 100W / 160W | +4.5% / −19.8% | Baines, 2014 |
| UVC emission | None detected; glass blocks below 295 nm | Baines, 2014 |
| Ferguson zones covered, 100W and 160W | All four (Zones 1–4) | UV-Tool, JZAR 2016 |
How much UVB does a Mega-Ray lose over a year?
A self-ballasted Mega-Ray — the type sold here — lost about 15% of its UVB output over its first full year, and about 17% after 18 months of daily use. It started at 280 µW/cm² at 12 inches, read 240 µW/cm² at twelve months, and 233 µW/cm² at eighteen. After the first week it decayed by less than one percent a month.
Burn-in — the sharp early drop most UVB lamps show — was measured on seven lamps and averaged 3.5% (range 0.6–5.7%) over the first 90–105 hours, which the report calls “extremely low for a UVB-emitting lamp.” For comparison, it notes: “we have tested other well-known brands of mercury vapour lamp which have decayed as much as 60 – 70% in their first 100 hours.”
Method. Nine lamps supplied by the maker between 2004 and 2006; a Solarmeter 6.2 broadband UVB meter plus a UV-VIS spectrometer; burn-in charted on seven lamps and long-term decay recorded every 1,000 hours on three.
The limits, stated by the tester. Only two lamps ran a full year, so the long-term sample is n = 2 — and the second lamp, an externally-ballasted type that is no longer made and that we do not sell, lost 66% in a year and 82% by eighteen months. Her own conclusion on the pair: “results are less conclusive with one lamp decaying by 66% but the other by only 15%, which is a remarkably low rate of decay… In yet another respect, mercury vapour lamps appear to be a very variable product.” The test lamps were provided free by the manufacturer, and the 2006 report’s author’s note describes the team as “interested amateur herpetologists” offering “personal opinions” — research-grade equipment, but not a laboratory certification.
What has been measured on the bulbs sold today?
The 2006 lamps were an earlier design. The current coated PAR38 100W and 160W were re-tested in October 2014 with a Solarmeter 6.5 (UV Index), 6.2 (UVB) and 8.0 (UVC) plus an Ocean Optics spectrometer. Over the first 105 hours the 100W showed a 4.5% increase in output averaged across all distances and the 160W a 19.8% decay — “neither of these figures are cause for concern.”
Two findings from that report are the reason we describe the bulbs the way we do:
- No UVC, no non-terrestrial UVB. “These lamps appear to be constructed from glass which effectively blocks wavelengths below 295 nm, but transmits significant amounts of UVB in the wavelengths required for vitamin D3 synthesis. There was no evidence of any UVC or non-terrestrial UVB.”
- A wider beam than a bare PAR38. “The application of an inner semi-transparent coating effectively diffuses and spreads the light, creating a considerably wider beam than is usually possible with a PAR38 bulb.”
What this report does not give us: any long-term decay figure for the current design. The 15% and 17% numbers above come from the 2006 self-ballasted lamp. Nobody has published a measurement of today’s lamp beyond 105 hours — including us, and including the manufacturer. The same report also warns that readings above UVI 8 close to the lamp are levels “I would not recommend for use over live animals,” which is why minimum distance is not optional.
Our own replacement guidance stays at every 6–12 months, or whenever a UV Index meter says the output has fallen below your species’ zone — regardless of what the decay data suggests is possible.
Is Mega-Ray rated for my species’ Ferguson zone?
Yes, for the 100W and 160W, according to the only peer-reviewed assessment that includes them. The BIAZA UV-Tool (Baines et al., “How much UV-B does my reptile need?”, Journal of Zoo and Aquarium Research 4(1): 42–63, 2016) was co-authored with staff from Chester Zoo, Marwell, the Zoological Society of London, Durrell and Bristol Zoo. Its Table 2 assesses 24 lamps used in reptile husbandry, and lists “MegaRay PetCare — Mega-Ray 100W (2014)” and “Mega-Ray 160W (2014)” as able to provide a suitable UV Index for all four Ferguson zones — Zones 1 and 2 by the shade method, Zones 3 and 4 by the sunbeam method, depending on distance. Only five lamps in that table of 24 reach Zone 4.
| Zone | Typical basking UVI range | Maximum UVI recorded in the wild |
|---|---|---|
| Zone 1 — shade dwellers / crepuscular | 0–0.7 | 0.6–1.4 |
| Zone 2 — partial sun / occasional baskers | 0.7–1.0 | 1.1–3.0 |
| Zone 3 — open or partial sun baskers | 1.0–2.6 | 2.9–7.4 |
| Zone 4 — mid-day sun baskers | 2.6–3.5 | 4.5–9.5 |
Bearded dragons sit in Zone 3; red-eared sliders and other basking turtles in Zone 3–4; leopard geckos, crested geckos and corn snakes in Zone 1. Which wattage that translates to is on our which bulb for which species guide.
How far from the animal should each bulb sit?
These are the manufacturer’s own figures, from the distance and species letter supplied with our wholesale account. Measure from the face of the bulb to the animal’s back at basking height — not to the floor of the enclosure.
| Wattage | Minimum | Maximum | Optimum |
|---|---|---|---|
| 70W | 6″ | 12″ | 8–10″ |
| 100W | 12″ | 20″ | 14–16″ |
| 160W | 18″ | 24″ | 20–22″ |
| 275W | 30″ | 48″ | 36–42″ |
At minimum distance the bulbs produce roughly 150–200 µW/cm² UVB and 900–1,200 µW/cm² UVA; at maximum distance, 50–70 µW/cm² UVB. A mesh screen between bulb and animal deflects 20–40% of light, heat and UVB, so a lid means moving the lamp closer within the range. The manufacturer’s own caution is worth quoting: “All too often our clients mistake ‘minimum distance’ with ‘optimum distance’.”
The 275W is described by the manufacturer as a zoologist’s bulb, “NOT INTENDED FOR PERSONAL USE unless you need UVB within the optimum distance of the bulb for your habitat” — at a 36–42″ optimum it suits tall or institutional enclosures only. Mounted at typical home height it would badly overdose an animal.
Sources
- Baines, F. (2006). ReptileUV Mega-Ray Mercury Vapour Lamps for Reptiles — Test Report. UV Guide UK. Archived copy (the original site’s certificate has lapsed).
- Baines, F. M. (16 October 2014). Mega-Ray 100W and 160W test results. Reproduced in full on Our Reptile Forum.
- Baines, F., Chattell, J., Dale, J., Garrick, D., Gill, I., Goetz, M., Skelton, T. & Swatman, M. (2016). “How much UV-B does my reptile need? The UV-Tool, a guide to the selection of UV lighting for reptiles and amphibians in captivity.” Journal of Zoo and Aquarium Research 4(1): 42–63. Read the paper.
- Mega-Ray distance and species letter, supplied to wholesale accounts (figures in the distance table above).
Common questions
How often should a Mega-Ray bulb be replaced?
Every 6–12 months, or when a UV Index meter shows output has dropped below the range your species needs. Independent testing measured only about 15% loss in a year on a self-ballasted lamp, but that was a single lamp of an earlier design, and no long-term data exists for the current bulbs. Replace on the calendar unless you own a meter.
Do Mega-Ray bulbs emit UVC?
No. Spectrometer testing in 2014 found no UVC and no non-terrestrial UVB; the glass effectively blocks wavelengths below 295 nm while transmitting the UVB range used for vitamin D3 synthesis.
What Ferguson zones can a Mega-Ray cover?
The peer-reviewed BIAZA UV-Tool rates the Mega-Ray 100W and 160W as able to supply a suitable UV Index for all four Ferguson zones, depending on mounting distance — Zones 1 and 2 using the shade method and Zones 3 and 4 using the sunbeam method. Five of the 24 lamps assessed in that table reach Zone 4.
Not sure which wattage or how far away? Our species-to-wattage guide maps the manufacturer’s own table to common pets, and you can email us with your enclosure dimensions before you buy. We stock the 70W, 100W, 160W and 275W and nothing else.
