Thermal bulbs

Thermal bulbs are all light sources that generate light from heat. These include the sun, incandescent and halogen incandescent bulbs

The Incandescent Lightbulb

Incandescent bulbs are the original form of electric lighting developed in the 19th century (see history). The first bulbs contained a carbon filament which was later replaced by a metal filament. In the 20th century, as a result of ongoing technical improvements, the incandescent bulb is widely used in all lighting fields.

An incandescent bulb typically consists of a glass enclosure containing a thin thread of coiled tungsten filament. Electric current flows through this conductive material, heats up and produces light. Light from an incandescent bulb is only a by-product, most of the energy (about 85-95%) is converted into heat. This heat ensures a high infrared content in the incandescent light, which provides the "feel-good factor".

Incandescent light bulbs usually contain a stem or glass mount attached to the bulb’s base which shields the filament and allows the electrical contacts to run through the envelope without gas/air leaks. Small wires embedded in the stem support the filament and/or its lead wires. The bases are standardized throughout Europe (E27 or E14), they work well on either alternating or direct current, so they can easily be used in any standard lamp/luminaire.

The colour rendering of the incandescent lamp is excellent, warm and easy on the eyes. Incandescent bulbs are compatible with dimmers, light up immediately when turned on and generate little electro smog.

As of 2009, many incandescent bulbs stopped being manufactured because they are being phased out of the EU and other countries due to their inefficient energy use. However, this only affects bulb production and there is no time limit on the sale of these incandescent bulbs which means they are still readily available in retail stores and on the internet.

Technical Data
Power: 25 to 1.000 watts, depending on the bulb
Luminous flux: 730 lumens at 60 watts
Luminous efficacy: 12-15 lm/W at 60 watts
Energy efficiency: E (from A++ to E, the lowest value in terms of efficiency)
Colour temperature: 2300 K bis 2900 K (warm white)
Colour rendering: 100 CRI (of 100, which is the best colour rendering value)
Lifespan: approx. 1000 hours



Incandescent bulbs do not draw any reactive power. They are simple and inexpensive to produce, easily disposed of, and free of mercury and heavy metals. They do not have a warm up period and come on at full brightness as soon as you flick the switch. Their luminosity does not deteriorate over time. Incandescent bulbs do not flicker, are easy on the eyes, promote sharp vision, cause no background noise, dim easily, have a sun-like full colour spectrum and the best possible colour reproduction.


Most of the energy is given off as heat, not as light.

Life span 1.000 hours? >>

In 1924, a group of leading lighting manufacturers in Europe and the US (including General Electric, Philips, Osram) established the 1,000 hours life limitation of the incandescent lamp when they founded a supervisory body called the ‘Phoebus cartel.’.

The Phoebus cartel, the first global cartel which later became highly controversial, introduced many of the current industry standards, such as the E27 and E14 sockets for incandescent lamps. Establishing a standard lifespan had a practical background - comparable parameters were created between the conflicting factors of lifetime, brightness and power consumption (longer lifetime meaning weaker light). Critics accused the cartel of preventing technological advances that would produce longer lasting light bulbs. It is indisputable that this cartel made decisions based on economic interests.

The Halogen Bulb

Halogen incandescent bulbs (low and high voltage halogen) are also thermal bulbs. They have been available since 1959 in many styles and forms, some of which are presented here. In these bulbs, the incandescent filament is very small compared to the incandescent bulb and is embedded in a quartz glass flask filled with halogen gases (iodine, bromine). The gas provides higher light output, longer life and reduces energy consumption.

In the case of high-voltage halogen incandescent bulbs, a small piston with gas is usually located in an incandescent glass bulb with an E14 or E27 socket. There are variants with G9 pin socket: these very small lamps, not enclosed in glass, may be sold without restrictions, even after 2018, because of their relatively high energy efficiency. Halogen lamps with R7 sockets (which are small glass rods, used among others in ceiling spotlights) are also among high-voltage halogen incandescent bulbs still on the market.

Low-voltage halogen bulbs, which have an even higher luminous efficiency and lifetime, are similar to those with a G9 socket (socket G4, 5 or 6 - unlike the G9 socket with round-bent metal connections, the low-volt socket has straight pins to plug in). These bulbs require a transformer e.g. usually found in the food of a floor lamps. Low-voltage halogen bulbs are often used for lighting systems such as recessed spotlights and ceiling spots. As with all bulbs powered by transformers, there is an increase in the electro smog.

In terms of quality, light from a halogen incandescent lamp is comparable to that of an incandescent lamp: it is slightly lighter overall, has excellent colour rendering, dims easily in the high-voltage version and largely electro-smog-free.

Technical Data: Low-voltage halogen bulb
Voltage: 12 volts instead of 230 volts for all high voltage lamps
Luminous flux: 770-1650 lumens
Luminous efficacy: 15-27 lm/W
Energy efficiency: B (from A++ to E, i.e. significantly higher in terms of efficiency)
Colour temperature: 800 K to 3000 K (warm white)
Colour rendering: 100 CRI (of 100, the best colour rendering value)
Lifespan:: approx. 4000-5000 hours
Technical Data: High-voltage halogen bulb
Power: depending on the bulb, 46 W corresponds to 60 W
Luminous flux: 700 lumens at 46 watts
Luminous efficacy: 10-19.5 lm / W
Energy efficiency: C-D (from A ++ to E, i.e. average value)
Colour temperature: 2700 K to 2800 K (warm white)
Colour rendering: 100 CRI (of 100, the best colour rendering value)
Lifespan:: approx. 2000 hours (twice as long as an incandescent light bulb)



High-voltage halogen incandescent bulbs are similar to incandescent bulbs: do not draw any reactive power, do not flicker and contain no mercury. They are well suited for spot lighting, generally silent, dim easily, have a sun-like full colour spectrum and the best possible colour reproduction.

Low-voltage halogen incandescent lamps can also be used in bathrooms or kitchens because of the low voltage. They are durable, consume relatively little power and are not affected by the phasing out as most energy-efficient thermal bulbs in class B.


Even with the high-voltage halogen incandescent bulbs, a lot of energy goes into heat not light. Iodine and bromine are harmful gases, however are only present in small amounts.

Low-voltage halogen incandescent bulbs always require a transformer and a special dimmer, which may be susceptible to interference, cause disturbing noise and electro smog.


Complete phase out of halogen bulbs in 2018! >>

The EU's Eco design Directive implemented regulations to phase out halogen bulbs (no longer being manufactured, but no time limit for selling off old stock).


  • low-voltage halogen bulbs (12V, 24V), efficiency class B
  • high-voltage clear glass halogen bulbs with base G9 and R7s, efficiency class C

Discussions for further regulations are underway regarding the phasing out of almost all light sources except LEDs by 2020 due to increased energy efficiency targets. Input and entries are being accepted until the summer of 2018.

We are putting together contributions to these discussions. We welcome competent supporters and co-contributors.

Important: sign the e-petition to preserve the halogen bulb – more signatures mean more chance of political change!