Grow light test – charting the progress of tomato seedlings growing under a home made reflector and low wattage lighting.

For many years I have started my plants off sowing seeds into various types of multi-purpose compost, initially in the airing cupboard ( 25 centigrade ) and hopefully transferring to a heated propagator on a well lit purpose built bench beneath a large Velux window.

Whilst controlling temperature and moisture have not been too much of a problem controlling light levels has always proved to be difficult.

However, recently I have discovered lamps (photo below) that emit light closely matching the spectrum of daylight and having a high light output (1900 lumens). The lamps only cost about £8.00 each they fit in a standard bc or es lamp holder and only consume 30 watts each.


In order to maximise the light reaching the plants a reflector was constructed using an old propagator cover which I lined with kitchen foil and at one end a hole was cut in the plastic cover to fit a bc lamp holder, care being taken to avoid any contact between the foil and the electrical supply to the lamp. The other end of the cable to the lamp was terminated in a standard 13 amp plug fitted with a 3 amp fuse.

Propagator lid becomes a reflector
Propagator lid becomes a reflector

The lamp is then controlled by timer such that it extends the ‘daylight’ hours to 16 per day as well as providing light from within the room to compensate for the window light which normally causes the plant stems to lean towards the natural daylight.

The seeds were sown on March 3rd into a 24 cell ‘Rootit’ windowsill propagator, 16 cells with different varieties and thereafter repeats of those that I was more keen to try. These have been placed in an airing cupboard at around 25 degrees centigrade until they just germinate. Then they will be placed in a heated propagator at 25C but with the addition of the lights.



The whole set up is shown in the photos above. Please be very careful carrying out the simple electrical lamp wiring. Start by wiring the connections to the lamp holder first and those to the plug last of all. If in any doubt ask a qualified electrician. I will report results as the experiment progresses. Alan Box

Update 26th March 2013

Below is a photo of tomato plant progress so far. A good germination, 22 good seedlings from the 24 seeds sown of various varieties.


The grow light comes on at 4.30 am and off at 8.30. The temperature of the the Root-it sponges is measured to be a fairly constant 16 centigrade.

The sponges are kept moist using the Root-it first feed solution regularly. The constantly cloudy skies are an advantage at the moment as the plants could otherwise get too warm in direst sun through the velux window.

Very soon the plants will be moved on to 3 inch pots.

Update 1st April 2013

The Root-it sponges add a whole new concept to this as the process is now so easy. No compost falling from the roots as well as a firm entity to hold without fear of damaging the seedling.


The sponge can be held with complete confidence that the seedling will not be damaged. Moreover if you are tempted to add a little mycorrhizal fungi it is easy to apply. In any event I have now transferred my 22 Root-it seedlings to 3 inch pots.


Three types of compost have been used and clearly identified by writing on the side of the pots. I distrust labels that can be misplaced or lost altogether.

One of these compost types has to be a peat free due to my involvement with the National Trust. Perlite has been added to the composts to improve drainage. I would have preferred larger pots but there is not sufficient space in my propagator. Moreover larger pots are less likely to tip over when the plants get taller, so I shall have to be careful.

I have also transferred 7 other seedlings to 3 inch pots. These were sown conventionally in multi-purpose compost.

Update 13th April 2013

Some tantalising bright spells over the past week, but weather still depressing. I am convinced my lights have thoroughly proved their worth.

In fact the plants are progressing a bit too well in relation to my readiness and that of the weather, unless the Good Lord has something special his sleeve.

The photo below shows a set of healthy, sturdy plants of fifteen varieties.

I have to admit to being quite proud of them. I am inclined to stroke my hand over them releasing that wonderfully characteristic summer tomato plant scent.

I believe the Japanese advocate this stroking action to improve plant sturdiness, so I’m not really that odd.

Update 14th April 2013
I am continuing with my grow lights as before but extending their operating time to 6 hours, the plants remain in the propagator trays minus the lids.

In order not to loose the effectiveness of the lamps or the reduced daylight I have set up the improvised reflector screens using my Wife’s clothes Airer to which I have attached three disused but carefully opened McCoys crisp bags with the inner reflective surface facing towards the window light!




Update April 28th 2013
I have been pleased with the results due to the lights and the resultant ability to extend the pseudo daylight hours to around 16 per day. From the experience I have gained I might in future deploy two lamps instead of just the one, thus increasing the light level to 3800 lumens.

I would sow the seeds on or about 20th March instead of 3rd as I did this year. I may even sow on two dates spaced either side of the 20th. I am however stuck for space as the plants grow. My heated propagator raises the compost temperature to around 65 degs F.

I would lower this during the day. I found that I had made the compost a trifle too wet. Without removing plants to check moisture levels this is a difficult judgement to make.

The plants reached an average of 10 inches a little too tall and straggly for my liking, but very healthy. Plants sown elsewhere on bottom heat with no artificial light did not grow anything like as well although they were sown on the same day.


Other plants of the same variety were sown about two weeks later in a large commercial greenhouse on the very top shelf. In this house the air is heated day and night with a 2.8kwh turbo fan. These plants are way behind mine, but are shorter jointed and stockier.


The use of this high consumption fan heater is justified by the fact that there are hundreds of seedlings of all sorts being reared in this house.

My plants are now in their summer quarters and I am looking forward to a spectacular yield just like I see on the websites! A chap can dream.