LED Lighting the short version

[nicebutdim]

After reading pages of in depth technical information I emailed the manufacturers as I was getting well out my depth.Isn't there something missing in all this detail I have pasted below, in it's entirety;

''it depends how many plants you have.

any of our standard lights will suffice. you can have them as close as you like , the further away the light the further is will spread.

if they are just normal plants then a 50w or 90w light will be fine at a ratio of 7:1



Many thanks and if you need any more information please ask



Kind regards

Keith

http://www.ctledlight.co.uk ''


There I was thinking there was far more complexity in it,than just doing as their reply suggests

[musa_monkey]

How far away is far ? 1ft?, 10ft ? 20ft?
Intensity lumens/Lux readings will reduce at plant level as the light source moves further away.

I would have thought that this has a factor in growth as much as wavelength and spectrum.

[simon]

I suspect that the manufacturers know and care far more about manufacturing lights than they do about using them.

[Dave Brown]

Isn't there something missing in all this detail I have pasted below, in it's entirety;

Just a bit, maybe an odd word or two

mmmm....... doesn't instill me with confidence. I started looking into it in a big way, as I was LED to believe that new technology LEDs would make growing in the dark possible. However, I was misLED. You would need the units about 1 ft above the plants to get the light intensity strong enough for good growth. An average £50 unit would light one seed tray

Yes the further away they are, the more the light spreads, but the intensity is massively reduced.

Liken it to heat from a radiator. Stand next to the radiator and you are warmed a lot, move away and the heat you feel drops off dramatically, same with light for plants. You can't trust you eyes as they adjust to the lower light levels by opening your pupils.

The ratio they talk of will be red to blue LEDs for balanced growth.

[Gareth Davies]

Here's a nice "pretty" light unit currently on fleabay but I don't really know if it would be any good. Just because a lamp looks blue, I'm not sure you could guarantee getting blue spectrum light off it. I'll stick with my metal halides for now.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

[ash101uk]

I bet you could knock one of them up yourself on a bit of veroboard and double the quanity of LED's.

I feel a winter project comming on.

[dyls]

The problem with power illuminator LEDs is they do generate heat. Not as much as an incandescent bulb, but semiconductor lighting's efficiency is currently slightly less than a compact florescent lamp, so yes - heat is generated. It's also generated in a very small area (the diode itself) and you don't want the junction temperature to exceed its maximum and the challenge is getting the heat away from this very small area. The cooler you can keep the junction, the longer the LED will last. (You'll note for the GU-10 and MR-16 style LEDs, the ones that replace halogen downlighters, the actual casing is an aesthetically-designed heatsink)

The trouble is veroboard doesn't do a great job of getting rid of heat. The manufacturers in their datasheet show PCB layouts which will sink enough heat (on standard FR4 PCBs) but this needs plated through holes etc. to conduct the heat away.

I've experimented with Luxeon Rebels on a home-etched PCB (hoping that in place of the PCB layout they specify, sticking an old Pentium heatsink on the reverse side of the PCB would move enough heat) but their life turned out to be a bit short, instead of the 50,000 hours you're supposed to get, I got less than 100 hours before the LEDs lost a great deal of their output (and ran much hotter). Which was an expensive lesson given each individual LED (which is about the size of a typical indicator LED, in other words about 3mm) costs around 5 quid!

Also to get the efficiency it's not enough to just use a current limiting resistor, since you'll waste a tremendous amount of energy in the resistor, what you need is a high efficiency switch mode power supply. They aren't hard to make - there's a good choice of ICs designed for this job which require only three or four external components, but you need to be good at soldering - they are all surface mount. (You can solder small SMD components with a normal soldering iron, it just needs practise and a bit of solder wick).

Since I experimented with the Luxeon Rebels, the cost of MR-16 (12 volt LEDs in a 12-volt "halogen" assembly) has fallen to such that it's not worth me even trying to roll my own PCB/power supplies unless I'm doing something very special. (Indeed, I'm gradually replacing all the halogen downlighters in my house with these LEDs).

[AndyC]

How far away is far ? 1ft?, 10ft ? 20ft?
Intensity lumens/Lux readings will reduce at plant level as the light source moves further away.

I would have thought that this has a factor in growth as much as wavelength and spectrum.

Absolutely right Alan, I did some measurements a couple of years ago, the results are in this thread

[musa_monkey]

How far away is far ? 1ft?, 10ft ? 20ft?
Intensity lumens/Lux readings will reduce at plant level as the light source moves further away.

I would have thought that this has a factor in growth as much as wavelength and spectrum.

Absolutely right Alan, I did some measurements a couple of years ago, the results are in this thread

Thanks Andy, good info in that link very useful to know.

[sanatic1234]

I do like the idea of this LED lighting but surely the cost of the electricity being used on these throughout the winter will be very very costly, especially with energy suppliers set to up the cost again?

[musa_monkey]

I do like the idea of this LED lighting but surely the cost of the electricity being used on these throughout the winter will be very very costly, especially with energy suppliers set to up the cost again?

Depends on the power rating. For instance my prop uses a 20W T5 bulb which gives circa 4k lux at 6" from the light and circa 1750 lux at the base of the prop. at 9.15p per kWh
(my present suppliers charge) thats costs me 31p per week to run 24/7 so in relative terms not that expensive.