Light Box

I should like to introduce to you the new lightbox model 36J, lovingly crafted from exotic woods from distant northern places, seasoned for anything up to two weeks.



The box has been cunningly disguised as a drinks cabinet and friends will be amazed when the doors are opened. Indeed, in summer, you will be wanting to use it for your drinks, with only a small adjustment to make the lights come on when you open the doors. This could be accompanied by music as an optional extra. It is conveniently fitted with a clean and 100% hygenic wipeable tray to catch all the little drips that mysteriously appear after little more than nine gins.



An added advantage of this elegant piece of furniture, is that when the local constabulary visit, you only have to explain that it is your drinks cabinet and they will not bother to search it for any illicit activities.

 

Oh you are so wickedly funny!

 

For the technically minded, the external dimensions of the above box are 24" high x 16" deep x46" long. Inside it just holds a growbag tray. The frame is made of 2" x 2" wood, and the panels are white plastic coated hardboard (from B&Q). The ceiling panel is suspended on chains so the height of the lights can be adjusted. There are 3 three foot tubes of 30 watts each, giving a total output of 90 watts over 4.1 sq ft. ie 22 watts per sq ft. The running cost for 90 watts 16 hours a day is �£4.50 per month.

What I have gleaned from an American "Growing under lights" forum is :-

1) There are specialist lighting systems, but they can be expensive. Fluorescent tubes are quite acceptable, incandescent bulbs are not. You don't need special bulbs for growing plants unless you are very serious.

2) All fluorescent tubes are rated at about 10 watts per foot. You lose out at the ends so longer tubes are a bit more efficient than short ones. Tubes are 5 times as efficient as incandescent bulbs, but compact and coiled tubes, used as substitutes for light bulbs, are only 4 times as efficient as their output drops off with time.

3) You need 20 watts of light per square foot. But most light will be lost if you do not use a light box, and have the tubes about 2 inches above the plants. A good light box might may allow up to 85% of the light to fall on the plants, but no box and plants a foot below a light without a reflector may receive less than 5% of the light.

4) You must have your lights on a time switch, on for 16 hours a day.

 

Love it Peter.

All I need is more space!

 

Are you going into production, Peter? We could all do with one, provided, of course, we have space, as Dave pointed out..... I know - the garage! :D After all, it was big enough to get a boat in at the weekend :rolleyes:

 

what about the mirrors you were suggesting?

 

I have spent quite a bit of time looking at this specialist American forum. And am convinces of the need to get as much of the light that comes out of the lamp onto the plants themselves. I think mirrors are the ultimate reflection media, reflective melinar film, as used in emergency hypothermia treatment blankets, is apparently just about as good (but where do you get it), aluminium foil is probably next, but a white coated surface is also pretty good.

I used the white panels because they were cheap, light, and easy to cut. The box seems to work quite well. I have a little light meter that Walnut put me onto, and it shows that the light level in the box is pretty constant everywhere and does not drop off with distance as it would without enclosing panels.

 

Outdoor pursuits shops used to sell the reflective film under the name of Rosco blankets (there may be other brands) and it was very light and dirt cheap! I used to use it as a lightweight photographic reflector on field trips photographing flowers.... OK as long as it's not windy! Otherwise it was a Lastolite or an unpaid assistant if you could con someone into going with you!!!

 

Start saving the bags from inside wine boxes PeterS its very similar material to the stuff survival blankets are made from.
It also provides a good excuse for drinking wine :D

 

Cunning idea, Dave!

I've used those emergency things too, H-A - as you say - a very cheap alternative.

Peter - just had a thought - why 36J? I can believe in 36 being a dimension, but J? You surely didn't start with prototypes from A did you? :eek:

 

Dendro - Same reason you used to buy petrol with added WM7 many years ago. Means nothing, like most advertising copy, but fools the public. A bit like our chancellor who says we now have the lowest tax rate for 70 years. He forgets that last year 10% was the lowest rate, which he has just doubled. Sorry, on Mondays, Wednesdays and Friday I'm cynical - on Tuesdays, Thursdays and Saturdays I'm worse!

Thanks Hyla and Dave. Your comments prompted me to Google for the emergency blankets which I did find. They are very cheap, but p&p can cost more than the blanket. I will certainly take a look next time I pass a camping shop.