Mercury Vapour Lamps:
ZooMed Powersun UV 100watt Lamp
broadband meter readings and thermal gradient  
iso-irradiance charts
spectrum - UV + Visible light
spectral analysis - photobiologically active UV





Lamp Description

ZooMed Powersun UV 100watt Lamp
100watt, R95 self-ballasted mercury vapour lamp
ZooMed Laboratories Inc., 3650 Sacramento Drive, San Luis Obispo, CA93401, USA
ZooMed Europa, Klein Hagelkruis 13, B-2180 Ekeren, Belgium

                                                                                                          Lamp ref: BP19 (2012-2013)

Broadband Meter Readings

UV Index (Solarmeter 6.5) Total UVB (Solarmeter 6.2) and Illuminance (Lux meter readings)
New lamp (105hrs use)                                Distance from lamp surface (cm)
UV Index
Total UVB (µW/cm²)
4,260 3,270 2,590 2,060 1,680 1,420 1,200


Decay (reduction in UVI with use)
105 h (10 days normal use) 21%
no other data available
Electrical consumption 104 watts
Colorimetry (from spectral data)
CCT (human eye) 3,103K
CRI (Ra) (human eye) 61.2

Visible beam  (lamp to surface distance = 30cm)
The concentric rings drawn on the card are 5cm apart. This lamp produces a well diffused, wide beam.

Thermal Gradient  (lamp to surface distance = 30cm)
Surface temperature (°C) measured with infrared non-contact thermometer, on open bench.
Distance from lamp to bench = 30cm. Time to equilibrate = 2 hours

Distance from central point directly beneath lamp
0 cm 5 cm 10 cm 15 cm 20 cm 3 m (room temperature)
White wooden block 26.9 26.7 25.2 23.9 22.8 18.6
Unpainted wooden block
28.8 27.5 26.1 25.2 23.6 18.6
Black wooden block
30.6 29.4 27.7 26.2 24.3 18.6

At a reasonable basking distance in a well-ventilated vivarium, this lamp may be unable to create a sufficiently high surface temperature across a wide enough area to create a basking zone for sun-loving species. Additional lamps (such as incandescent lamps on a dimming thermostat) may be used to control basking temperatures.

Iso-Irradiance Chart       
The small tortoise (carapace length 15cm) is drawn to the same scale as the charts and is placed so that its eye level is 30cm beneath the lamp. This is solely to enable comparison between charts, NOT to indicate suitable lamp distances, which will vary according to individual species requirements.
NB: To help prevent glare and other eye problems from the visible light, and thermal burns from infrared radiation, even if UV output appears safe at close range, we also recommend a minimum distance of at least 30cm, and/or maximum irradiance around 100,000 lux (equivalent to very intense sunlight) from ALL mercury vapour and metal halide lamps.


This lamp has a very well-diffused, wide beam. This is creating a zone, at 30cm distance, that is approximately 40cm in diameter with a UV gradient between UVI 2.0 at its edges and UVI 3.0 at its centre.

Spectrum - UV plus Visible Light

A mid-day solar spectrum with the sun close to the zenith (Solar altitude 85.4°, location San Bartolomé, Gran Canaria, June 21st 2011 Local time 14:00h) is overlaid for comparison (but note the different irradiance scales).

Spectrum - UV in more detail

This spectrum has:

  • typical features of a mercury vapour lamp: extremely discontinuous spectrum ("spikes") very unlike sunlight.
  • no detectable UVC or non-terrestrial UVB (wavelengths below 290nm).
  • solar-wavelength (295 - 320nm) UVB output, restricted to "spikes" at 296, 302 and 313nm. These wavelengths are involved in vitamin D3 synthesis.
  • low short-wavelength UVA output (320 - 350nm). These wavelengths are involved in the control of vitamin D3 synthesis.
  • high long-wavelength UVA output, but restricted to one "spike" at 365nm - reptile vision includes long-wavelength UVA.
  • Visible light spectrum (wavelengths 400 - 750nm) mainly restricted to only four colours from the mercury arc, but with some additional continuous-spectrum light from the tungsten filament, primarily in the orange and red wavelengths - resulting in only moderate colour rendering (to the human eye).

Spectral Analysis - photobiologically active UV (wavelengths from 270 - 350nm)

  • There is significant UVB in the wavelengths which enable vitamin D3 synthesis in skin.
  • This lamp emits no hazardous UVC or non-terrestrial UVB (below 290nm).
  • There is some low-level continuous-spectrum UVB and UVA present, presumably from a phosphor in the inner lens coating.
  • However, compared to sunlight, the lamp has a greater proportion of its UVB in the shorter wavelengths. Hence the risks of cell damage (and also photo-kerato-conjunctivitis) from this lamp appears to be somewhat higher than with exposure to natural sunlight. This is a feature common to many brands of mercury vapour lamp. Caution is therefore necessary to avoid excessive exposure to this source of UVB.
  • The proportion of UVA from 320 - 335nm, important for natural prevention of excessive vitamin D3 synthesis, is very low. This is also typical of mercury vapour lamps. It is still unknown as to whether this has any long-term health consequences.



© 2013