Watts (W) are a measurement of how much energy a lamp/luminaire uses. Traditionally watts have been used to describe how much light output you would get from a lamp, however this is becoming more and more unreliable with newer energy efficient technology. For example, with incandescent lighting a certain wattage bulb would indicate a fairly accurate light output range, however with LED Lighting, due to differences in technology used, a wattage does not necessarily guarantee a set light output. For this reason, moving forwards lamps will start to be described using Lumens instead of Watts.
New energy labelling regulations now require the packaging to state the accurate Energy Consumption (EC) of the lamp, measured in kWh/1000h, if it differs from an already stated wattage. In the vast majority of cases the EC will match the Wattage value, however for any lamps with external ballasts or control gears (e.g. fluorescent tubes, 2D's etc) the EC will be a little higher than the wattage. This regulation is important moving forwards as lamps become being described in lumens, it is still important to know the energy consumption of the lamp.
Voltage (V, Volts) is the term used to describe the 'force' of electricity within the electric circuit. The most common analogy for voltage is the electronic-hydraulic analogy, or drain pipe theory, which likens the voltage to water pressure inside pipes.
The voltage of mains electricity supply varies around the world, with the UK, Europe, and the Far East being 220 - 240V, whereas the Unites States currently measures as 120V. In terms of Lighting, the voltage of the lamp simply indicates the voltage at which the lamp is calibrated to function.
In simple terms, the lumens (lm) can be thought of as the 'total amount' of visible light emitted from a source. For lighting the higher the lumens value of the lamp, the more light it emits.
Lumens are also used to determine the Luminous Efficacy of a light source (how efficient it is a producing light), by calculating the Lumens per Watt (lm/W) for the lamp. The more Lumens the lamp produces per Watt of energy used, the more efficient it is at producing light.
Colour temperature is a standard method for describing colours for use in a range of situations. Colour temperatures are normally expressed in units called Kelvins (K). Note that the term “degrees Kelvin” is often used but is not technically correct. The colour temperature is for descriptive purposes only and does not relate to the actual temperature of the lamp.
The following chart shows the colour temperatures used for some of the most popular lamp types:
Incandescent light bulbs have been around over a hundred years, and are what people think of as the traditional or classic light bulb. This type of lamp produces light when an electric current passes through a filament wire, heating it to a high temperature until it glows.
The term Incandescence refers to an object emitting light due to its high temperature, and it differs from Luminescence, which refers to the emission of light by an object which is below the temperature required for incandescence.
Due to this method of light emission, incandescent light bulbs are highly inefficient, with only ~10% of the energy used being turned into visible light, and the rest being converted to heat. The luminous efficacy of an incandescent bulb is around 16 lm/W, compared to an LED lamp which is up to 70lm/W.
Halogen lamps are a type of incandescent lamp (see above) using a tungsten filament, which are also filled with a small amount of halogen gas (e.g. iodine or bromine) in a capsule.
This combination of a tungsten filament and halogen case causes a reversible chemical reaction known as a Halogen Cycle to take place, this reaction causes the evaporated tungsten to form a Halide with the halogen gas. Once at a high enough temperature, the halide disassociates (breaks apart), which deposits tungsten back into the filament, thus extending the life of the lamp. This reaction also keeps the lamp clear (in an ordinary incandescent lamp the filament is deposited on the inside of the glass bulb, reducing clarity).
Compact Fluorescent Lamps are a low energy alternative to incandescent type lamps. These lamps consist of a glass tube filled with mercury vapour and gas, with an electrode at either end of the tube. When an electrical current passes through the gas, it excites the mercury vapour, which releases ultra-voilet light. Because ultra-violet light is invisible to the human eye, a phosphor powder coating is apllied to the inside of the glass tube, the ultra-violet photons interact with this phosphor coating, causing it to fluoresce. The colour temperature of the lamp can be varied by using different types of phosphor coating.
An electronic ballast is also required to limit the current in the circuit to prevent damage to the lamp. In the case of fluorescent tubes and most commercial type fluorescent lamps, the ballast is added external to the lamp, in the circuit or built into the fitting. For most compact fluorescent lamps the ballast is built directly into the lamp in its base, allowing them to be used as direct replacements for classic incandescent lamps in the same fitting.
LED Lighting is based on Light Emitting Diode (LED) technology, which results in lamps with significantly reduced energy consumption, but with lifespan and luminous efficacy several times better than that of both incandescent and CFL lamp types.
LEDs use what is known as a semiconductor to produce light when an electric current is applied to it. It produces light because the electric current causes electrons within the semiconductor to move around, which releases energy in the form of photons (light). The colour of the light released is dependent on the material used as the semiconductor.
Because most semicondutors produce coloured light, to produce 'white' light that we can use for domestic lighting, a mixture of colours or a phosphor coating (similar to CFLs) is used to create light that appears white.
The main component of an LED is a 'chip' of semiconducting material, a semiconductor has the electrical conductivity between that of a conductor (e.g. copper wiring) and that of an insulator (e.g. rubber). This semiconductor is doped (intentionally introduced) with impurities, which modify the electrical properties of the semiconductor, in this case creating what is knows as a p-n junction. This p-n junction consists of a p-type (positively charged) side, and an n-type (negatively charged) side, with the negative side having a high concentration of free electrons, and the positive side having a high concentration of electron holes (the conceptual opposite to an electron, or the lack of an electron where one could exist).
When an electronic current is introduced, electrons and holes flow into the junction, and when an electron meets a hole it releases energy in the form of a photon. The wavelength of the light emitted is reliant on the band gap of the semiconductor used. The band gap is equivalent to the energy required to free an outer shell electron from its orbit about its current atom nucleus, to become a mobile charge carrier, and hence join with an electron hole.
The wavelength of light is what determines its colour, so by using different semiconductors with different band gaps, we can vary the colour of light that is produced by the LED