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How Do HID Lights Work?

We’ve covered LED grow lights.

Now it’s time to talk about HID grow lights, and why we at BCNL strongly recommend them.

Over the past few decades, HID grow lights have become one of the most preferred products for indoor growing.

They’re more cost-efficient than other options on the market, and are tried, tested, and true.

So what are they?

HID grow lights work completely different from LED lights.

As we previously covered, LED grow lights are diodes, which are semiconductor devices. They rely on a conductor material called aluminum gallium arsenide and a voltage.

How LED grow lights work

HID grow lights rely on xenon gas and other elements like mercury and metal halide salts; yes, they are like the light bulbs from space.

Like HID grow lights, they do require a voltage, as it’s an electrical current used to produce an arc of light between two electrodes that are placed inside the sealed capsule.

The capsule is what contains the xenon gas and assorted elements.

HID grow lights don’t use filaments, which are what normal light bulbs have—you know, that little wiry thing in the very center of the bulbs.

The reason as to why they are so popular is due to the fact that they are 85% efficient. For one 35W HID light bulb, it can provide output in the range of 3200 lumens.

Breaking it down

There are four types of HID bulbs in total: mercury vapour, low pressure sodium, high pressure sodium, and metal halide bulbs.

We’re only concerned with the latter two.

High-Pressure Sodium HID lights

If we’re to be technical, high-pressure sodium lights, or HPS lights, aren’t really HID lights. They actually work like a fluorescent bulb, using low-pressure mercury or argon gases.

The main difference between low-pressure and high-pressure sodium HID lights is that low-pressure sodium HID lights produce a yellow light.

As we learned before, your “tomato” plants prefer the entire spectrum of light, from blues, to reds, to yellows, to greens. This renders low-pressure sodium HID bulbs less useful.

High-pressure sodium HID lights, or HPS lights, provide a more balanced range of the light spectrum when compared to other lights.

HPS lamps contain gases like neon or mercury, which is kept in the bulb’s inner arc tube. When a voltage runs through the inner arc and the gas will heat up first to produce a orangey pink light.

Then, slowly, as the sodium warms up, the light becomes brighter—which, as previously covered, though it may seem white to the naked eye, the white light is actually comprised of different wavelengths of the light spectrum.

High-pressure sodium HID light

In HPS lights, the yellow and red colors of the light spectrum are the most intense, with the other colors also concentrated.

And that—dun dun dun—is what your plants want and need: the full spectrum.

Though low-pressure sodium HID lights are more efficient in that it produces that yellow wavelength really well, it’s not efficient for the purpose of growing.

Metal Halide HID Lights

Metal halide grow lights, or MH lights, are high pressure and high temperature arc lamps. They have better efficacy than the other types of HID bulbs.

Like HPS bulbs, they have inner and outer tubes. The outer glass envelope encases the inner quartz arc tube that contains—you guessed it—metal halides! Sodium iodide is the most common compound used in the arc tube.

Metal Halide HID light

MH bulbs are further divided into two more subcategories: probe start bulbs and pulse start bulbs.

Using either an igniter (pulse start bulbs) or a voltage (probe start bulbs), the temperature of the metal halide compound increases, and the sodium and iodine separate from one another.

The result? Because of the metal ionizing reaction, reds and oranges are added to the lamp’s spectrum. This means that it has greater luminous efficacy.

Quick refresher: luminous efficacy means how well (or how poor) a light source makes light.

This is calculated through the ratio of luminous flux (measure of light visible to the human eye) that the bulb emits to power (which can refer to the total power the MH bulb uses).

What luminous efficacy shows, is really just the efficient of the energy conversion from electricity to light form.

And so, the greater the spectrum of light, the greater the luminous flux; the greater the luminous flux, the greater the luminous efficacy when compared to other bulbs and the power source is the same.

So how do you use them?

BCNL uses both HPS and MH grow lights for the best grows.

Because of its wide spectrum, MH grow lights are great for vegetative growth, and HPS grow lights are great for root growth and flowering.

In combining both, you are getting the most efficient grows without racking up huge electricity bills that may arouse suspicion.

So why not LED grow lights again...?

No, it's not just because we said so.

Instead, it's because we've tested the two against each other time and again.

Eldon Perdue, BCNL customer and our resident scientist, did an extensive experiment, and it showed that HID grow lights simply yielded more "tomatoes."

And that's what we're all looking for, isn't it?

More "tomatoes."

Want to learn more about Eldon's experiment? Read on here.

So what have you guys experienced with HID grow lights? Do you prefer them over LEDs?

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