Unfortunately, spectral shift is also an overlooked aspect of lighting technology.
But lamp life only conveys one aspect of long-term light quality: intensity. As certain grow lights age, their lumen output depreciates. At a certain point, that depreciation makes the lamp less effective for a horticultural application.
However, some luminaires also experience a light spectrum shift. A lamp that may have had the perfect blue-to-red ratio at the time of purchase may gradually produce less beneficial wavelengths.
So, how do HID and LED lights change over time?
Here’s a guide to spectral shift across a few different grow lighting options.
Understanding Rated Lamp Life
First, let’s take a quick look at the concept of rated lamp life. While this does not relate to light spectrum shift, these two considerations should work together to help you choose the perfect lamp.
The rated lamp life of an HID bulb indicates how many hours you can use that light before it is no longer operational. A typical lamp life for an HID luminaire is 10,000 hours.
For LED grow lights, rated lamp life indicates the point at which the light emits 70% of its original lumen output. While HID bulbs burn out, LEDs simply degrade very slowly over several years.
In other words, an LED lamp may still be operational without supplying the light quality your plants require. This does not mean LEDs fail sooner than HID bulbs. In fact, it’s quite the opposite.
High quality LED grow lights have a lamp life of 50,000+ hours compared to 10,000 hours for HIDs. To put it another way, LEDs supply the lumens your plants need five times longer than HPS and MH bulbs.
So how does the light spectrum shift for LEDs versus HIDs?
Light Spectrum Shift in HID Bulbs
When it comes to spectral shift, HPS bulbs demonstrate the most instability.
HPS (high-pressure sodium) lights are a type of HPS bulb that emits wavelengths in the orange and red spectrum. While growers occasionally use high-pressure sodium bulbs throughout the grow cycle, most choose to use MH for veg and HPS for flower.
Red light is essential for robust flowering and high yields. The challenge with HPS lamps is that the light spectrum shifts as the luminaire ages . . . and it happens fast. The spectrum moves away from the red end of the spectrum and veers into the green/yellow range.
Plants use very little of these shorter wavelengths for photosynthesis. This means an older HPS bulb is virtually worthless for any stage of plant growth.
How quickly does this light spectrum shift happen?
Well, most growers who use HPS bulbs replace their lamps at least once a year or once every two harvests.
Compare that to a quality LED grow light that maintains a consistent spectrum. Over the lifespan of one LED fixture, you would go through a minimum of ten HPS bulbs. That is certainly something to consider when calculating expenses.
Light Spectrum Shift in LED Grow Lights
None of this is to imply that all LED grow lights promise a consistent light spectrum over the life of the lamp. In fact, you can find spectral instability in plenty of LED grow lights.
You just won’t have that problem with premium LEDs.
The technology for spectral consistency in LED lamps is available to us. Cheap LED grow light manufacturers just don’t invest in that technology. Inferior light emitting diodes will change color with age . . . and that is only one of many reasons to avoid cheap LED lights.
The Best Option for Spectral Consistency
The bottom line:
If you want to avoid a light spectrum shift and get the most out of your lamp, you need to choose high-quality LED luminaires.
We have engineered our Optigrow spectrum to yield optimal results, and our commercial grade lights feature digital spectrum control. Above all, we only use top-shelf Osram LEDs to ensure 10-15 years of robust lumen output and a stable light spectrum.
Our U.S.-based team is always here to answer your questions about our products and horticultural lighting in general. Reach out anytime.