Artificial grow lights

When Should I Use Artificial Grow Lights?


If you’re an avid gardener, you know that natural light is crucial to the growth of your plants. But what do you do if you live in an area with limited daylight or have a short growing season? Artificial grow lights can help you optimize your results and give you more control over your growing environment.

If you have a limited growing season, you’re short on outdoor space, or you want more control over your growing environment, artificial grow lights can help you to maximise results.

Do plants grow better in artificial light?

Artificial grow lights are an excellent substitute for natural light and can help boost the early growth of your chillies and other crops. Using a sunny windowsill has some benefits in the spring, but in the winter months, the amount and intensity of light are insufficient to support early germination and growth. That’s where artificial grow lights come in.

Crops like chillies and tomatoes require a long growing season, and getting a decent harvest when you live in areas with short seasons, or limited daylight can be challenging. If this is an issue, artificial grow lights can be a good solution.

Whilst using a sunny windowsill has some benefits in spring, in winter months, the amount of light and the intensity of the light is insufficient to support the early germination and growth of your chillies. The further you live from the equator, the shallower the sun’s angle, reducing the light intensity, so it’s all about location, location, location.

A significant benefit of using artificial grow lights is that you can use them anywhere you have power. Most people will use them in the home or a greenhouse. You may have a small corner in the shed or garage you want to use; many grow lights can help you utilise the space to grow your own fruit and vegetables. I’ve set up artificial grow lights in my potting shed, which gives me much more control over the growing conditions for my chillies as it’s a much smaller space than my greenhouses. I can manage the light and temperatures at this critical growth stage for my plants.

Grow lights can also extend your growing season. If, like me, you’re keen to become as self-sufficient as possible, you can use grow lights to grow salad and vegetables all year round.

When should I start using grow lights?

You don’t need to use grow lights as soon as you’ve planted your seeds. As long as the soil is warm, your seeds will get the energy they need to germinate. However, as soon as your seedlings sprout, turn on your grow lights.

Once seedlings have emerged from the soil, which is an exciting time for any gardener, they’ll start looking for light. If the light isn’t readily available, your seedlings can begin to reach for more light and get leggy.

With artificial grow lights, you’ll help your seedlings to grow strong and healthy from the outset. You want to give your seedlings the best start to life and reduce their risk of dying. If you’ve watched any of my youtube growing series, you’ll know that I find it so upsetting to throw away any plants, so I do everything I can to ensure they begin life as sturdy seedlings.


If your seeds haven’t germinated within a few days of planting, you may want to add a grow light to be safe; you don’t want to miss the first shoots breaking through the soil.

I’ve been growing chillies and other crops for many years, and I’ve tried many methods to get the best results. I swear by using artificial grow lights. When I transplant my chillies, I want to ensure they can grow into strong, healthy, highly productive plants. And, of course, these days, my livelihood depends on it!

How much light do my plants need?

You’re trying to replicate a summer day using artificial grow lights. Your plants need about 12-14 hours of artificial light and some supplemental natural sunlight. If they have no natural light at all, you may need to have your artificial grow lights on for 14-16 hours.

The amount of light your plants need varies depending on the growth stage and other environmental factors. Daily Light Integral (DLI) is the total light a plant receives in 24 hours, measured in moles per metre squared, per day. How much light a plant can absorb in 24 hours depends on plant age, health, temperature, humidity, and CO2 levels. More detail on the exact dose of light your plants need can be found below, so be sure to keep reading.

Grow lights are manufactured to focus on a small part of the light spectrum, optimised to be effective during critical growing stages, such as in vegetative growth and flowering/fruiting.

Understanding that humans and plants process light differently when selecting artificial grow lights is essential! Human eyes are sensitive to yellow and green light, whereas plants are sensitive across the entire light spectrum. Because we process light differently from plants, lights that appear bright and intense to us are often ineffective for plants.


As discussed above – if you have a good amount of outdoor space, you do not need to use grow lights for the entire season. It would be best to have them once your seeds sprout and until the weather improves enough for you to transplant them outdoors or into a greenhouse.

What is the best type of artificial grow light to use?

The best lights designed for horticulture to get the best results when growing crops. Fluorescent lights and LEDs offer the most effective light intensity you need and are designed to be more efficient than standard household lighting.

Fluorescent lights are great for early-stage growth but may only be up to the task for part of the growing season. They are my favourite types of lights to use for young seedlings!

The best lights for horticulture are fluorescent lights and LEDs. Fluorescent lights are great for early-stage growth but may only be up to the task for part of the growing season. LEDs are more efficient than fluorescents and offer more control over light intensity throughout the growing season. They’ve also become more affordable and typically last longer. Below are a few recommendations, if you’re looking to purchase lights:

Whats the difference between Lux, Lumens and PAR?


Below is some information on how we measure light intensity and the amount of light a plant can use; these measurements can help you make the best choice for grow lights. But, if you’re not confident in making the right selection, I can offer some guidance based on the tests I’ve done on various grow lights, so if you want an honest review, check out my lighting videos.

As you can see by the above image, lumens give a bigger bias towards the light spectrum that humans are sensitive to, namely green and yellow. Whereas PAR measures evenly across the visible spectrum of light, including the ends of the spectrum, that plants react well to (red and blue).


Lumens measure light intensity, but lumens measure human sensitivity to light, so lumens alone are not useful for plants. There’s a saying, “Lumens are for humans”!

LUX (Luminous Flux)

LUX is a measurement of how many lumens are falling on a surface area of a metre squared. Lux will help you gauge where the light should be positioned in relation to the canopy of your plants.

PAR (Photosynthetically Active Radiation)

PAR is a rating that is more important for plants. It refers to the wavelengths of light that plants use for photosynthesis. PAR is typically measured in micromoles per square meter per second (μmol/m²/s), and it is an essential metric for growers to ensure that plants receive enough light energy for optimal growth. The three terms commonly used when discussing PAR measurements are PPF, PPFD, and μmoles.

PPF (Photosynthetic Photon Flux)

PPF refers to the total number of photons emitted by a light source each second, measured in micromoles per second (μmol/s). PPF is a measure of the amount of light energy emitted by a light source, but it does not take into account the area over which the light is spread. Therefore, it does not provide an accurate measurement of the amount of PAR available to plants.

PPFD (Photosynthetic Photon Flux Density)

PPFD is the amount of PAR that reaches a specific area, measured in micromoles per square meter per second (μmol/m²/s). PPFD takes into account the area over which the light is spread and is a more accurate measure of the amount of PAR available to plants. To measure PPFD, a PAR meter is used, which measures the amount of PAR that is reaching a specific area at any given moment. The reading on the PAR meter is in μmol/m²/s.

How far away from my chilli plants should a grow light be?

You should position your lights depending on the type of light and the crops you’re growing. You’re aiming for around 2500 lux at the canopy of your chillies, increasing to 6000 lux after a month.

Remember that leaves have a limit to how much light they can absorb every second.

So depending on the stage of growth, I’d recommend the following amounts of light:

  • Seedlings – no more than 100 µmol/m2/s
  • First few months after germination – no higher than 400-500 µmol/m2/s
  • Fully mature plant – 900-1200 µmol /m2/s

As I mentioned, PAR meters are expensive, but if you’re using a modern, full-spectrum LED grow light, then the graph below may help:


I correlated readings from a cheap Lux meter and PAR meter readings. If you get a cheap Lux meter, these measurements will help indicate the light levels to aim for. Remember, the recommendations in the graphs above are a safe starting point. Feel free to increase your light output, but do it gradually over a period of days and monitor the health of your plants.

Below are a couple of links to PAR and LUX meters I would recommend if you’re keen to monitor your growing environment closely:

Your plants will tell you if they’re not getting enough light, they’ll start reaching to try to get more light and become unhealthy and weak.

Equally, if they get too much light, you’ll see signs of bleaching, curling up, darkening or even burning of the leaves. Take care not to give your plants too much light, as you’ll end up with an unhealthy plant, and it may even die.

Adjust the brightness of your light until you get the readings you need based on the stage of growth of your plants. If you aren’t able to adjust the brightness of your lights, then move them closer or further away from the canopy of your plants (Light intensity follows the inverse square law, meaning if you double the distance of your lights from your canopy, it reduces the light to a quarter of its intensity)

If you want more details on light measurements, then watch this dedicated youtube video:

When should I stop using grow lights?

The ultimate light for plants is natural sunlight, so you should stop using artificial grow lights as soon as you can get your plants outside safely. Your seedlings should be strong and healthy, and you’ve seen the last winter frosts.

Introduce your seedlings to the great outdoors in stages. Move them outside for a few hours daily, steadily introducing them to sunlight to harden them off. You can increase how long you leave them outside over time.

Be sure to put your plants back under the grow lights when you move them back inside. If you stop using the grow lights, your plants will again start reaching for the light, and you’ll risk them getting leggy and weak.

Ideally, it would be best if you moved your plants outside a couple of weeks after the last frost – the last thing you want is for the frost to kill off your seedlings and ruin your season completely. Waiting until the right time will result in earlier and larger harvests.

Of course, if you have no or limited outdoor space, you may need to use your grow lights for longer or all year round.

Conclusion, When To Use Artificial Grow Lights?

So, if you’re keen to start growing your own crops, growing in challenging conditions, or looking to improve your harvests, then artificial grow lights can help you get started.

If you found this article helpful, consider subscribing for alerts when new articles are published; alternatively, watch my Beginners Guide to Growing Chillies, which includes information on grow lights and more.

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