Page 45 - Simply Vegetables Spring 2022

Metal halide lights give off a better light spectrum than the sodium and can be used on their own in garages or cellars as plants will get nearly the full spectrum, but they are not as energy efficient as the sodium lights. The LED will give a full spectrum and the newer models are more efficient than both the sodium and metal halide lamps.
The current LED lights will give up to 3.5μmol/w depending on the spectrum and in the near future could be up to 4.2μmol/w which is close to the expected peak efficiency for the lights. You need to be aware of how much light a lamp will produce for the electricity consumed, some are more efficient than others. LED’s are better than the sodium and metal halide lamps. A 60% efficiency means that 60% of the energy is turned into light and the remaining 40% into heat; this may be useful for heating the growing area or may need dispersing by opening the ventilators.
As stated above red and blue light are most important to the plant:
Red light causes vigorous growth, but
if used on its own produces malformed plants. Blue light corrects this issue and reduces stretching, also chlorophyll production goes up and the stomata on the leaf open allowing transpiration.
LED’s costs are reducing and the efficiencies increasing and there is also a
wider range of choice so now could be a good time to consider trying lighting. When installing get a qualified electrician to do the cabling and connections, and set the lighting the correct height above the crop (see the instructions). Also consider when and how long you are going to switch the lights as this will effect both the electricity consumption and the plant growth. Allow for at what stage in the crops life to use the lamps i.e. seedling, young plant or mature plant or its whole life.
At present LED lights are used commercially on lettuce, microgreens, salad leaves, tomatoes, peppers, cucumbers and young plug plants as well as very widely used in vertical growing / farming. Experimental work has shown an increase in crop yield and quality by using LED lights. It is important to consider which wavelengths to use to get the best effect on the plants, and how long to use them for as well as the best photosynthetic photon flux density. There is some evidence that LED lights can affect and possible improve flavour.
There are tailor made lamps to produce the wavelengths to give the best results
for the crop being grown. LED lamps have been shown to give an increase in root and vegetative development, reduced apical dominance, manipulation of crop flowering, fruit initiation and the development of sugar levels in some crops. The effect varies depending on the wavelength and crop grown, there are now light recipes
for different crops. These recipes are a combination of light spectrum, intensity, hours used, and the time of day. Using
the correct recipe controls the flowering, gives a higher yield, better flavour, reduced vertical growth and better basal branching.
The use of lighting in greenhouses is for two main reasons, one is to supplement the natural lighting (solar radiation) and the other is to control flowering of certain crops (photoperiodic lighting) which as we are a
vegetable society I will not cover! Supplementary lighting is mainly used
during late autumn, winter and early spring when the day lengths are short and natural light levels low. By using lighting
it increases photosynthesis and therefore plant growth, yield and plant quality. As a rough guide 1% extra light equals approx. 1% extra crop by dry weight, important if you want large crops. Members will most likely want to use the lighting during the winter to early spring period when they are starting off new crops.
Supplementary lighting can increase the speed to harvesting which can be helpful for early crops and saving growing time – useful for crop planning. If using lights the crop can be spaced closer together giving a higher yield per area. Using lighting in the autumn can extend the growing period giving a longer cropping period which may be useful for certain crops harvested up to Christmas.
When growing young plants or plug plants supplementary lighting is very useful as it gives bigger plants quicker and also plants that flower earlier. The lighting levels can be affected by the region of the country and experimental work has shown higher levels are required in the north than in southern areas.
Hopefully the above has whetted your appetite and you can consider whether they will be of use to you and help you to produce more or better crops. Choose the right lamps and ask for running costs so you know what it will cost you to run them and you do not get a shock when your electric bill arrives! Consider which crops you will use them on, how many hours and which wavelengths are best for your vegetables.
This article was written before the recent increases in energy costs so check out the running costs carefully baring in mind likely future energy costs.
Salad crop on shelves with lighting
Simply Vegetables 45