Glossary of terms so you don’t drown in a sea of lighting acronyms

Imagine that a client enters your grow shop and asks if you have high-PPFD CMH lamps because they've just happened to hear about them somewhere. Would you know what to say and explain what that type of lamp consists of? The acronyms used in lighting systems for indoor cultivation are so common that many get lost in a sea of initials. Most derive from English terms and have become a standard in the world of indoor lighting.

CFL (Compact Fluorescent Lamp)

Compact fluorescent lamps are those fluorescent coiled bulbs that we've all seen before. They include a built-in ballast and a standard E27 base, which means that they can be screwed into any domestic light fixture. They emit white light but can showcase different colour temperatures.

Warm white lightbulbs normally have colour temperatures of around 2700 to 3500K, whereas the colour temperatures of cool white bulbs range between 5000 and 6500K. Cool light is more suitable for the vegetative period, whereas warm light is more appropriate for the flowering phase. You can also find lamps with an intermediate colour temperature.

K (Kelvin)

The kelvin is the base unit of temperature that indicates the colour spectrum of a lightbulb. It is known as colour temperature. The higher the number, the bluer the colour (cool light), whereas the lower the number, the redder the colour (warm light).

Edison screw (ES)

The Edison screw is a standard lightbulb socket for electric light bulbs. It was developed by Thomas Edison in 1909 under General Electric's trademark. This type of fitting is characterised by the designation Exx, where 'E' stands for 'Edison' and 'xx' indicates the diameter of the connector in millimeters. For instance, the code E27 represents an Edison screw connector with a 27 mm diameter.

T Fluorescents (Tubular)

These are the typical fluorescent tubes used in office blocks. The 'T' means 'tubular', and the number indicates the tube diameter in eighths of an inch. Therefore, a T5 tube has a 5/8 of an inch diameter, and a T8 has an 8/8 of an inch or 1 inch diameter. T5 fluorescent lamps are the most popular choice amongst indoor growers as they're highly efficient and are available in several colour temperatures.

HID (High Intensity Discharge)

High-intensity discharge lamps contain a tube that is filled with several gases and metal salts at high pressure. The lamp produces light when an arc is created between two electrodes in the gas mixture. The most common types of HID lamps include mercury, metal halide, and high-pressure sodium.

MH (Metal Halide)

A metal-halide lamp is a type of HID lamp. Its arc is filled with a blend of metal halides, which are compounds between metals and halogens (such as sodium chloride). This gaseous mix produces a white light similar to natural daylight. It leans towards the blue side of the spectrum, which makes this type of lighting ideal for the vegetative growth phase. Lumatek and Philips are two prominent brands in the MH lamp sector.

HPS (High Pressure Sodium)

A high-pressure sodium lamp is an HID lamp that contains a sealed arc tube filled with gases like sodium, mercury, and xenon. These gases light up and produce a light with a yellow, red and orange spectrum, which is great for stimulating flowering, and is the reason why many indoor growers use HPS bulbs during this phase.

CMH (Ceramic Metal Halide)

Ceramic metal halide lamps are an evolution from metal halide bulbs, and are becoming increasingly popular amongst indoor growers since they can fulfill a combined role between MH and HPS lamps. They are composed of a really hot ceramic tube that ionises several gases and salts. The exact composition of this mixture determines the lamp's light spectrum. CMH lamps have a really high CRI (up to 96), which means that objects look almost completely natural under CMH light. In addition, they also contain much more red light than a standard MH lighbulb.

LEC (Light Emitting Ceramic)

LEC is the term popularly used to refer to this new CMH-based (Ceramic Metal Halide) technology. The two terms are used indiscriminately, depending on the manufacturer, and must not be confused with LED lighting.

LED (Light Emitting Diode)

A light emitting diode is a solid device that produces light when an electrical current flows through a chemical compound so it becomes excited and lights up. This technology doesn't require the heating of any filament. LEDs are highly efficient as grow lights because they produce more power per watt than other light sources, and also generate less heat.

LED SMD (Surface Mounted Device)

The main difference between the various types of LED lights is their bulb structure. Every design is different to prevent even the smallest heat emission. This is paramount to guarantee a longer lamp lifespan. In contrast to traditional lightbulbs, which emit heat outwards, LEDs do it the other way round: they emit heat inwards, where the diode is located. The more efficiently the heat is diffused, the less the LED chip will suffer. LED SMD lights are based on a group of diodes on a printed circuit board encapsulated in a semi-rigid resin. They can include blue, green and red diodes in order to create different colour combinations.

LED COB (Chip On Board)

This is a newer type of LED technology. Several LED chips are mounted directly on a board so they form one single module. Individual LEDs are small and work as a single light source, but in this case they appear as a lighting panel rather than a group of small lights.

CRI (Colour Rendering Index)

Colour rendering index is a quantitative measure of the capacity of a light source to faithfully reproduce colours in comparison with a natural or ideal light source. It is measured on a scale from 0 to 100 (the higher the number, the more realistic the colours). Therefore, a CRI of 100 means that the objects under that light look exactly as they are.

PAR (Photosynthetically Active Radiation)

Photosynthetically Active Radiation designates the spectral range of solar radiation from 400 to 700 nanometers that plants and microorganisms are able to use in the process of photosynthesis. It is, therefore, closely related to plant growth.

PPF (Photosynthetic Photon Flux)

Photosynthetic Photon Flux measures the total amount of photosynthetic active radiation (PAR) emitted by a light source per second, i.e. it tells us the amount of light produced by the source that plants can actually use. The unit used to express PPF is micromoles per second (umol s⁻¹). PPF does not tell you where the light goes, but it's an important metric if you want to calculate how efficient a lighting system is at creating PAR.

PPFD (Photosynthetic Photon Flux Density)

Photosynthetic Photon Flux Density measures the amount of light that actually reaches the plants and therefore can be used by them (or only on a particular surface). It is measured using a PAR meter using micromoles per square metre per second (mol m⁻²s⁻¹). PPDF is the most useful measure to indicate how much usable light a source can provide to your plants.

UV (Ultraviolet)

Ultraviolet light is a form of electromagnetic radiation with a wavelength of between 100 and 400 nm (nanometres). UV light is classified into three main types: UVA (long-wave), with a wavelength of 315-400 nm; UVB (medium-wave), with a wavelength of 280-315 nm; and UVC (short-wave), with a wavelength between 100 and 280 nm.