Everything you need to know about grow lights

We all probably learnt in school that plants need light to survive and photosynthesise - of course if you're growing outside this will come from natural sunlight...but what about if you're growing inside? That's where grow lights (sometimes called propagation lights) come in. 

What is a grow light? 

Grow Lights are specially designed to provide seedlings, cuttings and young plants with the light they require to grow healthily, avoiding leggy growth and yellow leaves that can occur when there isn't enough natural light. Our Gardening Angels have put together a few of the most frequently asked questions about propagation lights to help you with your growing! 

What type of light is best for growing plants indoors? Can I use any light?

One commonly asked question is can you grow plants with regular light bulbs indoors? The answer is, not necessarily. For optimum growth, most plants need the right light spectrums, which might not be provided by typical household bulbs. Some houseplants will be fine but if you are propagating seeds and cuttings, or want to really boost the flowering stage of plants such as tomatoes and chillies, opting for some proper grow lighting is best.

What’s all this about light spectrums? What light spectrum is best for plants?

In order to properly grow, plants need two types of light - blue light to promote foliage growth, and red light to promote flowering and fruiting. Both types of light spectrum come from natural sunlight but not all bulbs will be the right type. When you're looking for propagation lights, you'll notice they'll be labelled with numbers like 2700k or 6500k, which is a reference to the where on the colour spectrum the light given off by the bulb is. A 6500k propagation light (like our propagation LEDs) will give off a 'colder' blue light, perfect for early growth, while a 2700k (like these flowering LEDs) will issue a 'warmer' red light to promote flowering and fruiting. 

You can also get full spectrum lights or dual spectrum lights, such as our T5 Propagation Lights and All Season LEDs. These lamps can be used from propagation right up until fruiting with no need to change to a different spectrum light.

How many watts do I need to grow plants or seeds?

Leafy edibles such as lettuces need around 30 watts per square foot, but fruiting plants such as tomatoes and chillies need a minimum of 40 to 50 watts per square foot. To work out what wattage you need, simply multiply the square footage of your growing area by the number of watts you plan to provide (between 30 and 50); then divide by the number of watts supplied by the bulbs you plan to use.

How close to my plants should a grow light be?

Ideally you should be placing your lights six to twelve inches over seed trays - our Vitopod Light Support Kit holds propagation lights at the correct height over your propagator for you.

How much do grow lights cost to run?

Both our T5 and LED lights are very cost effective to run - to get the best out of them you should bear in mind the environment they are in. If they are in a room with natural light coming in, you, of course, won't need to use them as much as if you have them in a dark room, shed or grow tent. 

The cost per hour for the lights depends on the light size and your unit cost per kilowatt. To give you a rough idea, our largest T5 Propagation Light uses 39watts per hour. You will typically be charged per kilowatt per hour, usually somewhere around 10 to 20p per kilowatt hour.

From this, you can see that the cost per hour is very low, even with two lights on your propagator.

How long should grow lights be switched on for?

When we look at how long to leave lights on for, we need to think about imitating the seasons. When in the propagation stage,  we’re trying to imitate the late spring/summer, so we’d suggest 16 to 18 hours light per day. It's important you don't give longer than this - vegetable seedlings need eight hours of darkness too!

To encourage blooming, we want to imitate autumn, shorter hours and redder light. The plants will think winter is coming so must reproduce. We can imitate this by reducing the hours of light to 12 hours per day and changing the lamp to the 2700k which is the (red) colour.

Worried about forgetting to turn lights on and off at the right times? Plug your grow lights into a programmable timer - this will turns the light on and off at the same time each day, ensuring the vegetable seedlings get the right amount of light.

What time of year should I use grow lights in?

Generally, your lights should be used during the dark winter months, when it's too cold to grow seeds outside and you certainly won't be getting 16 hours of natural daylight! We recommend using lights between the months of October to April in the UK.

What’s a lumen and how many do I need?

Lumens measure the light intensity output from lights - they're used to measure light levels and how well you'd be able to see in the dark based on the output. 

One lumen = one candle

When you're using grow lights you need to take into account spectrum as well as lumens as you need to know the type of light as well as how much light is given off. 

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 Featured Products: 

Sunblaster T5 Propagation Lights - From £30

T5 Propagation lights can be used over a propagator or seed trays at the start of the season to prevent legginess and yellowing, and then in autumn place them over mature plants to help with late stage growth and ripening.

The lights can be used as single units or up to 8 can be linked to cover a larger space and plugged into a single socket. 

Our lights use very little power thanks to their super-efficient nanotech enhanced reflector. The reflector increases lumen availability by 300% and diffuses light deep into the plant foliage.

Key Features

~ Typical lamp life: 10,000 hours.
~ Weight: 100g
~ The power cords have an on/off switch
~ Include clip-on fixing points for you to attach twine or a chain for hanging 

 

Blue LED Propagation Lights - From £35

Our LED lights for propagation deliver a blue light spectrum of 6500k. 

~ Complete - include a built-in reflector 
~ Long life, up to 50000 hours
~ Low running costs - Extremely efficient at converting power into useable light
~ Dust and splash resistant IP Rating: IP44
Link up to 7 light strips together to cover a larger growing area
~ 3 Year Warranty

These LED lights are available in 5 lengths, from 30cm – 120cm, so you can choose the best size for you. 

Red LED Flowering Lights - From £35

Our LED lights for flowering deliver a red light spectrum of 2700k. 

~ Complete - include a built-in reflector 
~ Long life, up to 50000 hours
~ Low running costs - Extremely efficient at converting power into useable light
~ Dust and splash resistant IP Rating: IP44
Link up to 7 light strips together to cover a larger growing area
~ 3 Year Warranty

These LED lights are available in 5 lengths, from 30cm – 120cm, so you can choose the best size for you.

 

Purple LED All Season Grow Lights - From £35

These brilliant LED lights deliver a purple dual light spectrum of 6500/2700k - this makes them perfect for all seasons.

Use them to give seeds an earlier and healthier start - no yellow leaves and no leggy stems. You can then also use them over more mature plants to help with late-stage growth and flowering. 

~ Complete - include a built-in reflector 
~ Long life, up to 50000 hours
~ Low running costs - Extremely efficient at converting power into useable light
~ Dust and splash resistant IP Rating: IP44
Link up to 7 light strips together to cover a larger growing area
~ 3 Year Warranty

These LED lights are available in 5 lengths, from 30cm – 120cm, so you can choose the best size for you.