Medwyn Williams gets to grips with lighting his glasshouse
Medwyn gets to grips with lighting the glasshouse over winter
Iremember sowing and growing exhibition onions with my father in a small greenhouse using a basic paraffin heater with no artificial form of lighting at all. How things have changed over the years! My first experience with lights were using regular ‘warm’ light fluorescent tubes, which was a huge improvement from having nothing at all. From there I moved on to building a growing cabinet and using Grolux and then on to a 400W Son-T agro high pressure sodium lamp.
Since I moved everything down on to the land and into the new glasshouse things have changed a lot. I now have eight 400W, high pressure, sodium, 4-T5 units as well as a single 315 ceramic metal halide lighting kit. This is a lamp that gives you as near to natural summer daylight as possible, giving you the best spread of colours. In order to improve further the light spectrum across the benches in the glasshouse, I’ve removed four of the high pressure sodium lamps and replaced them with Sumaster cool metal halide. There’s no doubt that lighting for plants is a complex and changing subject and one that I’m just about coping with.
For instance, when I was growing at home I used to check the light levels with a small meter that was giving me the LUX levels of lights. Nowadays the light levels are measured by PAR (photosynthetic active radiation) and good light levels are between 300 to 600 PAR. With the new ceramic metal halide I’m getting a reading of 600 at 45cm (18in) above the plant and 550 at bench level. Under the other lights at bench level I’m just about getting 300, which should maintain good growth. However, I’ve had to lower them down, which reduces the spread of the light at the fringes.
I did say it was complicated, didn’t I!