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Metal Halide Lamps

Metal halide lamps are excellent lamps for reptiles because …

  • … their spectrum is very close to the solar spectrum in the range 350 nm to 800 nm. This enables full colour vision for tetra-chromatic reptiles.
  • … they are very bright. It is easily possible to create a bright basking zone with up to 100'000 lux brightness - just as bright as the sun outside at a sunny summer day.
  • … the amount of visible light and infra red light is well balanced. In a distance, where 100'000 lux at the basking zone is reached, usually also the temperature comes close to the basking temperature in natural sunlight.
  • … the light looks beautiful. A terrarium with a metal halide lamps gives the impression of real sunlight.
  • … metal halide lamps are very efficient, the do not consume much energy.
  • … they are mass produced for lighting in retail industry, so they are reasonably cheap to buy.
Spectrum of 4200 Kelvin ceramic metal halide (Osram), CRI>90
Spectrum of 5000 Kelvin quartz metal halide (Osram), CRI>80
Spectrum of iwasaki metal halide, CRI=96

However, they do have some disadvantages:

  • They are largely unknown to most people. And most people do not like to use lamps, which they do not know.
  • You can not buy them in standard stores, especially usually not in pet stores.
  • Metal halide lamps can not be dimmed.
  • Metal halide lamps need a few minutes to reach full brightness when you switch them on.
  • Metal halide lamps need even more time to cool down, when you switch them off. So you need to wait 10-20 Minutes before you can switch them on again. The are “switch on in the morning and switch off in the evening” lamps.
  • The need a ballast. Most people only know household bulbs that have the ballast (if they need one) included in the bulb (leds, compact fluorescent “energy saving” lamps …).
  • They need high voltage to ignite and therefore need a special fixture and special cables.

These disadvantages are only minor in the context of terrarium lighting, and once you are used to metal halide lamps, the thing about the electrics does not seem that complicated any more.

Side note: UV-metal halide lamps, like the brands solar raptor, lucky reptile bright sun, … have a different spectrum. Their visible and UVA light is not as nice, the spectrum is spiky and the amount of UVA is quite huge.

Spectrum of 6000K UV-Metal halide lamp Lucky Reptile Bright Sun Desert

Different metal halide lamps and their usage

There is a huge variety in metal halide lamps for different applications. Metal halide lamps range from 20W to several thousand watts and come in different shapes and sizes.

Metal halide lamps with E27 fixture

These lamps seem easiest at the beginning, because they look like normal incandescent bulbs and also some reptile metal halide lamps from the pet store have this form. But often they are more expensive and you need to do all the electric wiring yourself.

Lucky Reptile Bright Sun
Electronic ballast Lucky Reptile Bright Control Pro

Although these lamps have a normal E27 base, they must not be used with normal (plastic) E27 sockets. Metal halide lamps are ignited with 5000 V and a normal E27 would not withstand this strain. You must at least use a ceramic socket, best is a socket that is specified for 5kV ignition voltage.

ceramic socket with label “4/250”: 4 A and 250 V - widely used for metal halide lamps but not ideal
ceramic socket with label “4/250/5kV”: perfect for metal halide lamps

This high ignition voltage and a stable current during operation is generated by the ballast. The ballast is switched between the wall plug and the lamp.

Two kinds of ballasts exist: Electronic ballasts and conventional ballasts. Conventional ballasts are heavier, sometimes make a buzzing noise, waste more energy, but are more robust against voltage fluctuations. Sometimes conventional ballasts are divided in three parts: A coil, sometimes called ballast, a condensator and an ignitor (pictures below). An electronic ballasts is always only one device, they are much lighter, consume less electric energy, sometimes they produce a high frequency noise. In most cases I would recommend electronic ballasts. The wiring is printed directly on the electronic ballast. Attaching the cables is technically very easy, but depending on the legal regulations in your country, your insurance and your willingness to take risks, you should ask an electrician to check your installation.

Always use a ballast that is specified for the same power as the lamp! Never use a 150W ballast or a 50W ballast for a 70W lamp! You risk an explosion of the lamp, and the lamp is filled with toxic mercury. Even if the lamp does not explode, the lifetime is reduced because the power does not fit to the lamp and the spectrum of the lamp is altered. Metal halide lamps do not function like normal incandescent household bulbs, so do not try to transfer your experience with these lamps to metal halide lamps!

electronic ballast: The white cable (bottom) goes to the wall plug. The black cable (top) goes to the lamp socket. Blue and brown wires are only interchangeable for the white mains cable, because the wiring diagram does not specify any direction. For the black cable to the lamp, the thick brown wire has to go into the top connector as the wiring diagram indicates with the flash symbol.
socket: the brown L-wire goes to the bottom contact, the blue N-wire to the ring contact.

The cable from the ballast to the wall plug is like any cable from any other household device. The cable from the ballast to the lamp socket needs to be a special cable for high voltage. It should at least be a cable that is thermally more stable than standard cables. Best is a cable that is specified for 5kV ignition voltage.

cable “SIHSI-J 3 x 0,75mm²” for high voltage between ballast and lamp socket. The l-wire is thicker in order to cope with 5kV ignition voltage.
standard cable that must not be used with metal halide lamps.
ceramic socket with standard cable after operating a 70W bright sun for several months. Photo courtesy of “obiwuff”

If UV-metal halide lamps are available in your country, you can use the installation sets that are sold for the metal halide uv lamps.

Metal halide lamps used with housing and external reflector

Metal halide lamps with a housing are more widespread and used in many stores (clothing, food, cars …) with a rail fixture system. The housing contains the socket for the lamp, a reflector and the (often conventional) ballast. The adapter for the rail can easily be removed using some force and replaced by a normal cable with wall plug. In some countries, these lamps can be bought very cheap, when shops close and the lamps are not needed any more. In Germany the best place to buy them is ebay. If you know where to buy these lamps in your country, please leave a comment! These lamps are often fitted with a conventional ballast. You can continue to use this ballast, but if the ballast becomes noisy or is to heavy for your setup, in most cases, there is enough space in the housing to replace the conventional ballast with an electronic one.

There are hundreds of different housings and different reflectors. Some make very good lamps for basking zones because the collect all the light and heat in a small area. Others diffuse the light and can be used similar to fluorescent tubes for general lighting. And some reflectors are just badly designed and do not give a nice distribution of the light.

Different lamps exist. First, there are quartz and ceramic lamps. Their spectra do not differ much (see above), but ceramic lamps have a slightly higher colour rendering index (>90) than quartz lamps (CRI ~80), and ceramic lamps are more efficient (brighter when using the same power) and live longer. When you by a used lamp that contains a quartz illuminant, you can continue to use this. But when you buy a new lamp, I would recommend a ceramic one.

There are dozens of different sockets for metal halide lamps. You need to buy the one, which fits to the housing. Widespread in Germany are TS and T sockets. TS is a two sided lamp. It is more widely used with reflectors that spread the light. T is a one sided lamp that is very good in a round reflector to create a basking zone.

ceramic illuminat (opaque), T-socket (one sided)
quartz illuminat (clear), TS-socket (two sided)

The housing usually has a clear glass front in front of the lamp. Never remove this glass front! It protects you and your pets from glass splinters in the rare event, that a lamp explodes. It also protects the lamp from water drops, which helps to prevent an explosion. An - also very important - it blocks UVC radiation from the lamp, in case the lamp itself does not have a proper UV-stop.

Metal halide lamp with circular reflector, this kind of reflector is usually good to create a warm and bright basking zone.
Metal halide lamp with circular reflector, this kind of reflector is usually good to create a warm and bright basking zone.

Inside the housing of a metal halide lamp with conventional ballast. a: condensator, b: ignitor, c: coil, d: screw that connects the isolation wire with the metal housing, e: lustre terminal to connect to a cable with wall plug.
Same housing with conventional ballast replaced by an electronic ballast

Metal halide lamp with broad and flat reflector that causes a light distribution similar to a fluorescent lamp. Can not be used to create a warm and bright basking area, but very good for general lighting of a terrarium.

Where to buy

For used housings for metal halide lamps, search “70 W metal halide” on ebay. In Germany you will find houndreds of used lamps that were used in retail lighting before. In other countries this might be different. If you see metal halide lamps in retail stores (clothing, fruit and vegetable section of a supermarket, cars, …) you could ask the owner, where they buy their lamps.

For metal halide lamps with an E27 base, search “Philips CDM R” in google.

Once you have find the first lamp, you will surely find more and search for the best price.

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en/hqi/hqi.txt · Last modified: 2019/02/23 16:34 by

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