Watt?

If you use, or are thinking of using HID lighting in any flavour, chances are it comes in one of the more popular formats.  A glass tube-in-a-tube, with an Edison (E40) screw fitting attaching it to the reflector.

Popular British sizes include 250w, 400w, 600w and 1000w variants.

I have seen HID lighting available in other power ratings but these tend to be the most popular.

 Who's the daddy..?

Its fair to mention at this stage, if HID is your chosen path the 600w is meant to provide the most efficient means of delivery in terms of cost-per-kilowatt, but for this example I’m going to use the 400w version.  Possibly the most popular and highly used HID in the UK.

So we set up our 400w HID, (either metal halide or high pressure sodium), and switch it on!  Man those babies are bright.

One to bear in mind if you are growing covertly for one reason or another.  There’s no bigger give away than streams of high powered light leaking out from behind a curtain.  Even more so if it’s orange like a street lamp.

  imagine this shining out through your curtains..

Ok so we got a 400w lamp which I would assume, gives off 400w of power?

Well, yes and no.

400w in total, is not necessarily what your plants see.

Remember those PAR watts from earlier?  These are the light rays which the plant can see, and use to photosynthesize.

Plants don’t see light the way we do, and its for this reason that indoor growers don’t use halogen lighting etc.  Whilst it may be very ‘bright’ if you shine it in your eyes, the wavelength the light is delivered in is all wrong for horticulture of any kind, (see technical looking picture above).   Put simply, the plants can’t see very much of it, so they can’t use very much.

In fact, of those 400 HID watts of power you pay for through your electricity bill, you only actually receive around 160 PAR watts down and onto your plants.

The other 240 watts are lost in light waves the plant can’t use, and heat.

Did I mention the heat?