A Light Emitting Diode is a two-lead semiconductor. When a suitable current is supplied, electrons pass from positive to negative recombining in electron holes within the device, releasing energy in the form of photons. The color of these photons is determined by the LED substrate material (AlGalnP or InGaN) where light is released.
Aluminium Gallium Indium Phosphide (AlGalnP) LEDs produce red, orange, yellow and IR light. Indium Gallium Nitride (InGaN) LEDs produce blue, green & UV light.
Unlike ordinary bulbs, LEDs do not have a filament that will burn out, nor do they get especially hot. For these reasons the lifespan end output efficiency of a LED surpasses all other forms of lighting technology.
LEDs emit narrow wavelengths of light, or wavelength "bands". This makes LEDs incredibly well suited for grow lights, as they can target bands absorbed by plants with the highest efficiency. LED output bands typically span 20-30nm depending on the color.
Example: the 630nm red LED has more than 60% of its energy contained within the 620-640nm region; whereas the 470nm blue LED has more than 60% within the 455-485nm range.
Unlike traditional lighting sources that have plateaued in efficiency (output per watt), LEDs have continued to get more powerful and less expensive over time. This is known as Haitz's Law, which demonstrates that every decade since the 1960's, lumen output has increased 20x per decade, while the cost per lumen has decreased 10x per decade. This gave LEDs the power as of the late 2000's to topple the mighty HPS (High Pressure Sodium) for indoor gardening, and makes them a more powerful alternative today.
The efficiency of LEDs varies greatly from one manufacturer to another. In Hydro Grow's testing we have found up to a 60% PAR output difference between our LEDs and lowest tested, top-bin LEDs from manufacturers including Cree, Osram, Philips, Nichia, Seoul and LEDEngin.. This means that despite emitting the same wavelength with the same power, Hydro Grow tested 60% higher than the lowest recorded in that group!
There are several reasons why efficiency varies so much from one supplier to another. Each LED packaging company has their own unique LED "package" (shown on left). Each package consists of a heatsink, LED chip, bonding wires, lens and silicone encapsulant for the lens. While Hydro Grow focuses on having the largest heatsink and lens, most of our competitors have sought to miniaturize their packages to fit in tighter spaces. This reduces efficiency.
Testing (graph below) shows that our Hydro Grow package delivered 59% more 525nm green light (61.8µmol vs 25.6µmol) at the same power setting (700mA) as Cree. The reason for this is simple: Hydro Grow uses more efficient chips on a larger heat sink, allowing for lower temperatures, resulting in higher output. Our larger lens redirects light more efficiently than the Cree lens, resulting in higher optical efficiency. No matter which competitor we are compared to (Cree, Nichia, Osram) Hydro Grow is miles ahead in PAR output for horticultural LEDs.
The size of the heat sink in a LED package is limited. The more watts a LED consumes, the more heat is generated. The more heat is generated, the less efficient the LED becomes. For this reason Hydro Grow uses only 3W chips, as they are the most efficient for LED grow lights.
As a rule of thumb 3W LEDs (700mA) are more efficient than 5W LEDs (1000mA), are more efficient than 10W LEDs, etc... In fact some LEDs (like the Osram example to the left) deliver more light at 3W than they do at 5W!
Different colors of LEDs degrade (fade) at different rates depending on temperature. The optimal temperature for any LED is below 25°C (77°F). Above this temperature light output begins to drop from 100% to less than 40% based on color. Amber, red and green fade the fastest, while blue holds intensity well regardless of temperature.
After a LED has finished the encapsulation process it is tested on a machine to determine it's exact color and total light output. The LED is then "binned" based on the results of this testing. So just because one LED looks like another, does not mean it performs the same. The highest output LEDs are known as "Top BIN", while the lowest are known as "Low BIN".
The data above compares various Luxeon Rebel LEDs from Philips. All LEDs are the same 630nm wavelength, but the 0030 bin emits only 62 lumens at 700mA, whereas the 0050 bin emits 102 lumens. That's a 40% difference! Notice as well that the 0030 bin costs only $1.54 per LED, while the 0050 bin costs $2.36 (35% more). This is how some competitors are able to cut costs on their grow lights without cutting the wattage they consume, to give the illusion of being more powerful but failing to deliver in performance.