Out with the old...
Consider this; a traditional filament bulb works simply by heating up the filament to such a temperature that it begins to glow red hot and emit light. The only reason it does not instantly burn out is because the glass bulb has no oxygen, required for the process of burning.
With a filament bulb, 90% of power is used to make heat, only 10% emerges as light!
In fact, 70% of the light that is produced, is directed away from the front of the bulb, so for growing applications, its neccesary to reflect the light. Not all of this light will be able to be reflected effectively to the target, but that which is will undergo a loss in the reflection.
Filament bulbs are consequently not popular with growers,but it helps to overview the above as HPS lamps share some of these problems.
Filament Lamp
High Pressure Sodium Lamp
High Pressure Sodium lamps (HPS) are popular with growers for their good spectrum coverage, however they require a lot of power and share some of the negatives of filament lamps, such as an omni-directional output. Lifetimes for HPS lamps is usually below 20K hours. As much of the light produced is targetted in the wrong direction and much of the wide spectrum produced is not useful to plant growth, you consequently need very power-hungy lamps in order to deliver enough "useful" output to the plants.
In with the new...
LED's are completely different in concept. They are designed with seminconductor technology and work by exciting electrons across a semiconductor junction. The excited electrons literally transform to photons across the LED's junction ; emmiting photons = emmiting light. The photons also leave in an orderly direction - only from the front of the LED, not in all directions like a bulb. This means no reflectors required and efficiency is much improved, more of the light produced will get directly to the target.
Here is a direct comparison for growers;
600 W high pressure sodium lamp = 120W LED grow light
400 W high pressure sodium lamp = 90W LED grow light
You can see why the LED solution will generate much less heat and electric bill costs to do the same job. Its a massive difference, some of it being attributed to the points already mentioned above, and the rest because of the capability to "tune" the LED output wavelengths to produce only light that is useful for plant growth.
Light that is "useful" for plant growth?
The chart above shows the absorption spectrum for plants. The wavelength on the horizontal scale represents the frequency or colour of the light in the light psectrum. There are several peaks of interest - these are the "sweet spots" in the spectrum, particular "colours" of light, which plants need in order to grow and to flower.
The blue region of 430-450nm and the red region of 650-670nm are most important, light at these wavelengths is most effectively utilised by plants.
LED's produce narrow spectrum output, i.e they can produce a red where all output is within a short range of 660nm, 450nm etc. By using the right combination of the right LED's it is possible to hit the "sweet spots" in the above graph and trigger plant growth and flowering.
The real advantage is that no light outside the prescribed LED range's is produced - there is no energy wasted producing light that is not effective for plant growth.
In comparison high pressure sodium lamps produce an intense but wide spectrum of wavelengths - in order to deliver enough juice to those "sweet spots", its necessary to use for example a 600W HPS unit.
In combination with the points mentioned above, its clear that LED technology is a winner for delivering serious growing results with minimal running costs. Heat generation- which has its own knock-on costs, is virtually eliminated.
Why LED's ?
Lower cost to run than HPS
10'000 hour min. lifetime
Less heat generation
Excellent growing results
No need for ballasts, extraction or reflectors.
Easy grow-room setup
120W LED = 600W HPS !
90W LED = 400W HPS !
For more information on LED House lights please visit: www.ledhouselights.co.uk