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LED grow lights or HID grow lights one of the most frequently asked questions that we get on this site. To figure out which one is better we need to understand what makes an LED grow light and what makes a HID grow light. LED grow lights are the new guy on the block, they promise excellent results with low heat and power consumption but do they really work?
Lets first see how they work. LED lights were first introduced by NASA to efficiently grow food for astronauts in space. They are ideal for NASAs application because of the low energy usage and low heat generation. LEDs can be thought of as tiny light bulbs but that is where the similarity ends instead of using a filament that can burn out they use the movement of an electron inside of a semiconductor to generate light. This also has the added benefit of a superior life span of the bulb lasting thousands of hours. LEDS are super-efficient they only generate light in the wavelengths that are needed by the plants so LED lights can be much lighter yet still generate excellent growing results. The down side to LEDs are their relative costs. To effectively replace a 600 Watt HPS grow light system you would need a grow LED unit that runs about $500. Also some plants might react worse to LEDs then to normal HID lighting but occurrences of that are very rare.
Now lets see how a HID system works. HID systems consist of two different types of bulbs Metal Halide (MH) and High Pressure Sodium (HPS).
The metal halide bulbs consist of an arc tube within the bulb (This is also referred to as a burner by some people). It contains Argon in most cases, mercury and various MH salts. The metal halide bulbs start when the ballasts gives off a very high starting voltage This ionizes the gases in the bulb and then a current is run through the arc tube which ignites the bulb. As the gases get hotter they expand and increase the pressure inside of the bulb. This causes an the bulb to get brighter and brigher also during the last stages it created ultraviolet radiation. The ballast must regulate the starting voltage / current and be able to maintain a stable operating current.
As you can see the above requires and immense amount of energy to be used. A lot of energy is wasted in heat and in light spectrums the plants don’t use. Also the bulbs have to be replaced when they start changing color over time. The upside is the units are relatively cheap to purchase and they do truly give out the best results.
To recap:


Low heat signature

Low energy usage

Lost lasting LED bulbs (50,000 hours plus)


High initial cost

Less than stellar performance.

Might need multiple expensive units for Growth / Flowering stage

HID Grow Light Pro

Low initial cost

Excellent proven performance

Suitable for virtually all types of plants

HID Grow Light Con

High Energy Usage

High Heat generation

Bulb life span of 10,000 hours max before replacement

As you can see you have a difficult choice and which system is better for you really depends on what you are growing and your scale. In either case to get the best results you should be using a grow tent or grow box to control the heat levels, smell and humidity for your plants specific needs. A grow tent will help you direct hot air out and cool air in, it will increase the size of your plants and the amount they flower. It is one of the best investments you can make in any growing project.