LED or HID lights? Important questions to consider

LED or HID lights? Important questions to consider

LED or HID? In this article we will try to help you understand the differences between these two lighting systems, to help you choose the most suitable system for you. 

List of contents

1.What is LED technology?

2. Technical specifications of LED for cultivation

  • PAR (photosynthetically active radiation)
  • PPF or photosynthetic photon flux
  • PPFD or photosynthetic photon flux density

3. LED and HID

  • Intensity and spectrum
  • Energy efficiency
  • Illumination and reg frequency
  • Distance between light and plants
  • Energy self-sufficiency

4. Final considerations


In today's article we aim to reflect on one of the most important aspects of indoor cultivation, lighting. If you are new to growing, you will have seen that there are several options, not only in terms of light output, but also in terms of the type of lights you can find. Today we will focus on the most popular ones, namely LED panels and traditional HID or high intensity discharge (sodium vapour, metal halide lamps, etc.).

With this post we are not claiming that LED panels today are better or worse than the rest of the grow lights, but simply that they are different options (with very wide price ranges) from which the grower will have to choose according to his needs and growing conditions. However, given the improvements in LED equipment in recent years, it is very likely that this type of lamp will conquer the market in the near future.

Modern LED fixtures, such as this Solux DreamCatcher 720W, have excellent performance and a very competitive price.

1. What is LED technology?

LEDs (light-emitting diodes) are diodes that emit light by means of a semiconductor through which a DC voltage is passed. Nowadays there are various LED technologies for cultivation, all of which are more efficient than traditional HID (high intensity discharge) lighting methods, making them a much more environmentally friendly, durable and economical option in most cases.

A few years ago, with the appearance of the first LED panels, a hopeful future opened up in the field of horticulture; many people were exchanging information in forums and trying their hand at creating these types of lamps in an artisanal way, and although there was not a lot of information, it was felt that they would be the way of the future.

Well, it took a few glazes to prove that in most cases (not always) they are the best choice. Quite the opposite of the early days, when efficiencies were not 100 per cent satisfactory and sodium lamps (HPS) were unrivalled, appropriate spectra were not very clear due to lack of research and purist defenders of discharge lamps and gearboxes criticised them to death.

Once you realise that you want to grow with LEDs, the most important thing to keep in mind is the right choice for your space. There are many platforms and companies that offer LEDs at really low prices, with results that look more than promising, but in most cases they do not deliver what they promise: that 1000-2000W LED equivalent to the output of a standard 1000W HPS with a power consumption of 150-220 or 300W does not exist, so forget it. To verify that it is a suitable system for cultivation, it is necessary to examine the light that can be assimilated by plants by consulting the data sheet.

In LED technology we cannot use the traditional measurement system, we have to abandon lumens, candelas and lux and start using measurements such as PAR, PPF and PPFD. It is important to choose the right equipment and make an investment you will not regret; the most likely thing with cheap equipment without technical specifications is that you will only waste time and have to buy another piece of equipment in the future.


2. Technical specifications of LED grow lights

Here are the data that should be offered by LED grow lights in the data sheet:

PAR (photosynthetically active radiation)

This is one of the most important points: PAR measures the light required (scientists call light 'electromagnetic radiation') for plants to carry out their photosynthesis.

Light is defined by different wavelengths, which are responsible for the formation of the spectrum. Well, PAR and FFPD are the part of these light spectra (electromagnetic radiation) that plants can assimilate (use) to carry out their photosynthesis, depending on several important points: the amount of light produced by our LED equipment, how much the plants can assimilate, and the amount of light the plant receives during the photoperiod.

Thus, PAR is the energy required for plant mass production by plants, the wavelength for green and exuberant growth, and is somewhat higher for optimal flowering; it is between 300nm and 800nm, the so-called physiological radiation.

PPF or photosynthetic photon flux

The PPF measures the total amount of light emitted by our LED equipment per second (the amount of PAR emitted) and the measurement is expressed in μmols/second. We could say it is the equivalent measurement to the lumens of traditional HID fixtures, but in PAR light, because lumens are actually used for the human eye and PPF for plants.

PPFD or Photosynthetic Photon Flux Density

The most important unit to consider when growing with LEDs is the photosynthetic photon flux density, known as PPFD. It measures the amount of PPF in a given area, which is what we need to focus on when choosing our LED based on the growing area (μmol/m2/s). It is subject to several variables besides area, such as the distance between the LED and the plants' spots, or the type of material used on the walls of our culture (reflection). By adapting our LEDs to the plants, using a good material (with good reflection) for the interior walls or reducing the cultivation area, the PPFD also increases.

3. LEDs and HID

Now that we know a little more about LED lighting and its measurement methods, we will make a brief comparison with HID, sodium vapour lamps (HPS) and metal halide lamps (HM) in cultivation.

We will look at all the factors to be taken into account to be successful in indoor cultivation in a grow tent. Lighting, ventilation (intake and extraction), temperature and humidity, irrigation and marinade, and preventive phytosanitary treatments.

Intensity and spectrum

LED panels are, in most cases, dimmable in intensity and have a full spectrum (the older one of growth and flowering), so they are good for carrying out the complete plant cycle. With conventional HID equipment, the bulb options available are: Mercuri (HM or metal halide lamps for growth), Sodi (HPS for flowering) and mixed (growth and flowering). However, we must bear in mind that after the first harvest, HID bulbs start to lose efficiency. With LEDs, on the other hand, many manufacturers guarantee up to 60,000 hours of use without losing efficiency and a 5-year guarantee on their equipment. During this time, many HID bulbs have to be replaced in order not to lose efficiency, resulting in money being paid back (production decreases with HID equipment from the first recall).

Due to the full spectrum of most LED equipment, a goat's head grown under LED has a terpene quality very similar to that of an outdoor cultivation, developing a much fuller aroma than using other types of lighting.

Energy efficiency

Speaking of shortage, an important factor to take into account is heat loss. We all know that energy is neither created nor destroyed, but transformed; therefore HID lamps transform a large part of their energy into heat (not just lumens). This fact can be positive or negative depending on the grower's situation; it loses efficiency, but in places where temperatures are low it can help to maintain the correct values within the crop, whereas with LEDs the ambient temperature will vary too much due to their poor heat generation.

In colder places we will have to use some kind of heater or install the cultivation tent in the right place, while in spring-summer it allows us to grow our crops without problems of high temperatures, at the same time as in HID cultures we will have to turn off the lights or install an air conditioner because of the high temperatures they generate. It must also be borne in mind that, due to their temperature output, HID lamps cause a considerable drop in humidity if the plants are not in good shape and generate adequate transpiration, which is why in many cases a humidifier will be necessary in the growing and pre-flowering phase.

With the concept of converting energy into heat (much greater in HID bulbs) we can already deduce that there is a loss of lumens, unlike LEDs, which enjoy greater PAR and efficiency. Every grower knows the temperature and humidity parameters of the location of his crop, so he will have to choose the most convenient system.

A word of advice: Because of the boom in the cultivation of automatic indoor plants, they need a photoperiod throughout their life cycle of 18 hours of light and 6 hours of darkness to achieve optimum results, Hydroponics recommends the use of LED panels for this task, because with a HID system on 18 hours a large amount of heat is generated and it is difficult to maintain the right humidity for the first few weeks (which should be around 75%). On the other hand, we have to take our lighting company's bill into account; 18 hours of light per day is a lot for a HID...

Lighting and fertilisation frequency

As we have said, the higher the temperature, the higher the evaporation (low humidity), which is why HID crops have to be watered more frequently, resulting in more wasted fertiliser.

With LEDs you have to be careful about this, as plants do not drink as much, although working with lower temperatures and more PAR it is common for plants to need an extra supply of calcium and magnesium. It is important to bear in mind that it is important not to overdo watering when growing with LEDs, as excess water tends to evaporate more and the longer it goes on, the more it can cause nutrient blockages in the roots. We must water as much as necessary, without overdoing it.

Distance between light and plants

It is important to emphasise that in both HID and LED cultures we must leave a prudent distance between our light and the plants' spots. In the case of LED we can always bring it closer once the flowering period has started, but not too far away. If we do not have enough information about our LED from the manufacturer, the best thing to do is to start with a prudent distance of 30-45 cm from the vegetation and see the reactions; if the plants stretch too far in search of light, we will move it a little closer.

As the light emitted by LEDs is very similar to sunlight, the plants leave much less distance between nodes (they grow more compactly) than those grown with HID, offering much more optimal development/production. However, possible pests are much more comfortable under LEDs, which we cannot solve by observing/monitoring the plants and using preventatives.

LED lights are usually placed at a shorter distance from the plant spots than HID equipment.

Energy self-sufficiency

Last but not least, LEDs are currently not 100 per cent self-cultivating, which will change over time. Today, we can already find very good LEDs at a very competitive price that can be paid back in a short time, not only because of their higher efficiency and low maintenance (HID bulbs have a cost and the price of light is always higher).

4. Final considerations

We often don't think about it, but LED technology makes it possible to use a solar panel system or a wind turbine, which is practically impossible with HID lamps... Today, there are already growers who have a self-sufficient system of solar panels that allows them to be a little more independent from electricity companies, reducing their electricity bills not 100% but significantly thanks to LEDs and home photovoltaic systems, or by means of wind turbines.

If you are an experienced home grower or if you want to get started in the exciting world of cultivation, the options when it comes to lighting are numerous. It is a matter of choosing the most suitable one based on various growing parameters and, in particular, budget, although if we think long term, LEDs are perhaps the best decision at the moment.


Find here our wide selection of HID and LED lamps!

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