LED's as the future for supplementary lighting

A recession, fluctuating energy prices, peak oil, phasing out of old incandescents, cheap chinese imports, US dept of energy research and development of products,and as the danish capitalist model reveals, affordability...Seems like its a matter of time until most people who apply supplementary light to their plants will be using LED's. What do you think?:skp:

 

Here's what I think.

I'm all for energy efficiency and protecting the environment, but I am sceptical about the real impact of certain initiates.

With any of the more well known, efficient stuff, information about efficiency during use is widely available. We know that energy saving light bulbs use about 20% or less electricity than their incandescent counterparts, and we know that LEDs are very efficient and very long lasting.

What is less accessible though, is information about the energy and materials used in manufacturing the items, or what happens when they are ultimately disposed of after failure.

As a real life example, Top Gear did a review of a particular car that claims to be the most environmentally freindly, with good fuel efficiency and a very clean engine. They said that by the time they'd extract some mineral to go into the catalytic converter, produced some alloy that other cars don't use etc etc, they calculated the carbon footprint of the car over its expected life span to be about twice that of the average car in its class.

 

Ipso - I think that the answer will be yes in time, but not quite yet.

The key is how much light, measured in lumens, you get per watt of energy you use. The watt, of course, is also a measure of cost. I built a light box two years ago and in my research the following figures came up

Ordinary light bulb (incandescent)........ 15 lumens per watt
Quartz halogen................................... 24
LED (Light Emitting Diode).................... 25 – 50
Long life (fluorescent) light bulbs........... 55
Long fluorescent tubes......................... 70
Sodium street lights (yellow ones)........ 150

LEDs are still developing fast, so there was a range for them. The best LEDs are approaching long life light bulbs, which are still a bit less efficient than long strip lights. The most efficient of all are the yellow sodium lamps that are used for street lighting - though a lot of people don't like the colour. In my Googling, I did read that some research LEDs are approaching the 150 lumens per watt, but these are still in the research phase. My research was two years ago, so LEDs may have moved on a bit since then.

Currently, the most efficient lamps that are practical are strip lights. They are the most efficient for plants, but of course the same figures apply equally well to use in the house. A sodium lamp would still be the cheapest lighting of all in the sitting room - but not everyone would appreciate it. :D

Clueless has a good point about all the invisible aspects. But as LEDs are solid state it is quite possiblt that they will ultimately be very cheap to make and have a long life. - I think they have a good future.

 

Having written the above - I have just had a Google. Perhaps I should have done this before I replied. :D

http://members.misty.com/don/lede.html This site says that many LEDs are in the range of 20 to 45 lumens per watt, but that the most efficient currently available are in the range 80 to 100 - but I think these have some drawbacks - they may not be very practical.

A laboratory prototype of a white LED achieving 161 lumens/watt was announced on 11/19/2008.

 

As far as I understand it, lumens are a measurement of white light or the narrow band known as photosynthetically active radiation. This does not apply to lighting which emits only certain wavelengths such as LED.
Impact could also be measured within parameters including how much yield could be gleaned from a given area. With LED's it is possible to substantially increase the yield through 'stacked' growing within many glasshouses, placing lights near to the canopy, offering growers opportunities to utilise currently vast empty spaces within their(heated and illuminated) growing area...

 

Ipso - Thank you for your initial prompt into this area. I have had another Google and learnt a quite a bit more about LEDs. It's clearly a big and complicated area. You are right the colour is very coherent in the same way as in a lazer. Ie the colour is very pure as it consists of a single wavelength. But you can get several different colours, by altering the impurities in the semiconductor or by altering the voltage. This explains to me why you can get pure red and blues for example as well as what appears to be white light (which must be a mixture of several different pure colours). They are talking about lives of 100,000 hours, if you run them properly (overheating will fry them). This makes them potentially very attractive, but there are drawbacks. They are all low voltage direct currant, and that implies some additional inefficiency.

There has been talk of using them for house lighting - perhaps by means of a light emitting sheet rather than a bulb. But so far nothing seems to have come of it yet. You see them a lot in cars nowadays. I think this is because cars have 12 volt batteries, ie the low voltage, direct current, that LEDs need. Houses of course have high voltage alternating current.

You have a good point about stacked growing - but you could probably do that already with fluorescent lights. I built myself a light box and you could certainly stack several of them on top of each other.

 

Peter the ones I use are 240 v AC and are blue and red wave lengths they do work the problem being they need to be very close to the plant/seed so need to be adjustable.
http://www.gardenerscorner.co.uk/forum/showthread.php/you-can-growwith-19236.html

 

Hi Walnut. I was wondering about the AC bit - I couldn't find a direct reference to that. do you have to use a transformer. It could be that the current is rectified by the system, which implies a loss of efficiency. I think individual LEDs are low voltage - say 12 volts ( probably less), but 20 in series would add up to 240 volts. Though if they are in series and one failed it would cause the whole lot to fail.

I have just had another Google and come across LED floodlights - which implies that they really are getting some power through them. http://www.ledlightingproducts.co.uk/LED spotlights.htm However even though they are efficient at producing light, 90% of the electricity supplied to them will still end up as heat. And you can see some hefty heat sinks at the base of the floodlights. On another site it warned about the heat issue saying that overheating will quickly fry LEDs. It really is a fascinating subject, which has a lot of potential.

I think the problem of being close to the seeds is exactly the same for LEDs as for fluorescent strips or any other kind of light. Essentially its due to the loss of light as it flies out in different directions. This is the arguement in favour of using a light box, which reflects the light back, rather than just using a bare lamp. Its no different from heat. If your room is uninsulated you need to sit close to the radiator to get warm. But if the entire room (box) is well insulated the heat will be much more uniform around the room, and cheaper to run.

At the end of the day, the key feature is how much light you get out per watt of electricity input, and how much the devices cost. This light engine looks interesting http://www.litewave.co.uk/16w_led.asp It says that it gives out 1150 lumens of light for 16 watts - ie 72 lumens per watt. That puts it on the same level as a fluorescent strip light.

 

I wish I could understand it all because I would love one.Someone will have to sell a ready made one for me.

 

Hi Peter no transformer plugged straight into 240v ac, here is a site that has some information and has 240 and 110 supplied led's maybe of interest to Joyce as well.
http://www.growlight.cn/

 

Walnut - really interesting site. Reading their stuff, they do state that the individual LEDs are 12 volts DC, and that the do need a transformer which has some inefficiency. I suspect that they use a solid state rectifier, which won't be visible but allows them to package a number of LEDs into a unit that plugs straight into 240 volt AC. But that doesn't detract from its attraction.

On the light output basis, their 120 watt and 300 watt units are giving out about 35 lumens per watt, which is good but still only half that of a fluorescent tube. But as they point out much of white light is not used by plants, so its not a good measure. At this point, I find myself lost. My gut feeling as a physicist tells me that lumens per watt is important, but my gut feel completely leaves me when dealing with what a plant actually needs. I can only accept the research that has been done. But even that Chinese site is not very precise on the subject.

Before this thread came up (thank you Ipso), I had only seen LEDs as indicator lights on instrument panels and lately as white light torches. It is clear that they have progressed way beyond that. The future is Orange...and Red and Blue :D

But irrespective of the merits of the source of light, I think there is a need to conserve any light in a closed light box. And I notice that is what they do in their test report that I downloaded.

 

This is an area of technology which is progressing very rapidly. I commute to work by bike. My route includes a couple of miles of unlit country roads. When I started six years ago, the sensible 'big' lights I needed (without going into really silly money) were quartz-halogens with a rechargeable Ni-Cad battery pack. You can't buy those anymore as they have been entirely replaced by LEDs. About four or five years ago, I bought a secondary light (as the big lights don't last too long and take 9 hours to recharge!) which was LED. A mate at work bought one from the same manufacturer at the beginning of this winter. His (which was cheaper than mine) has one LED and is significantly brighter than my cluster of seven!

I suspect that the 'holy grail' the manufacturers are going for is a plug replacement LED for a standard bayonet clip bulb, with the transformer in the base. Instant cold light. And they last for ages.

Worth keeping an eye on.

As for any worries about inefficiency. Transformers are not 100% efficient, but they're a lot better than most 'machines'. An incandescent bulb is only about 10% efficient -- think about how hot they get. And the energy needed to make the device has to be factored into the price. If it's too inefficient they won't sell.

Steve

 

Just to pick up on some technical bits that have been missed here, and just for interest:

LEDs are diodes, which means they only allow the current to flow in one direction. If a unit is geared up for regular mains, then one of two things will be happening. Either there will be a bridge rectifier built in (a collection of four diodes arranged such that the output is always the same polarity regardless of the polarity of the input, or the individual LEDs will be arranged so that they are only 'on' during half the cycle when the AC current is in a particular polarity. In the latter, you can safely exceed the nominal current rating of the LED to get more brightness without overloading it, because it actually pulses with a cooling off break when the AC current is in the half of the cycle when the polarity is negative. Also they are unlikely to be taking the full 240V (which in actual fact is more 340 at its peak because the 240 is the RMS voltage - the average over the cycle), more likely there will be a regulator built into the unit. As the regulator and the bridge rectifier (if needed) as all just semiconductor devices, they can be made suitably small and packaged in the same overall packaging so it will just appear as a single unit.

To pick up on the colour issue. As someone said, you mix up certain colours to get white. It is quite simple, you need red, green and blue all of equal intensity and you get white.