How To Stop Losing Money With HPS (No, it's not switching to LED)

Let's get practical for a moment and talk about something every grower using high-pressure sodium (HPS) lamps needs to hear clearly: If your lamps have been running for two years or more, you are likely leaving substantial money on the table.

We often overlook how subtle shifts in lighting intensity and quality can quietly chip away at yield and profits. Consider this: a 5-10% decline in lamp performance can translate directly to a 5-10% reduction in crop yield. The math, as straightforward as it is overlooked, speaks volumes.

Let's Break It Down:

Imagine a single HPS lamp consistently yielding 2.5 pounds of flower at harvest. At a wholesale price of $1,500 per pound, that's $3,750 per lamp in revenue. (I've charted more realistic pricing for flower below because no one is still getting $1500 a lb!)

• At a 5% yield loss, each lamp only produces 2.4 pounds, losing you about $188 per lamp each cycle.

• At a 10% yield loss, the yield drops to 2.3 pounds, amounting to a $375 revenue reduction per lamp per cycle.

Extrapolate that scenario to a typical room of 100 lamps:

• 5% loss: A $18,800 dip in your harvest value each cycle.

• 10% loss: You're now looking at a $37,500 revenue decrease per crop cycle.

The replacement cost for 100 Premium lamps? Approximately $6,000. (I'll address the differences in lamp manufacture quality in tedious detail in another article.)

The Invisible Costs

Many growers I speak with understandably rely on standard PAR meters to determine whether lamps deliver adequate output. But here's a critical insight: a seemingly minor 8% drop in measured PPFD has been correlated with yield losses of up to 30%. 

Unfortunately, standard PAR meters alone can't reliably detect subtle shifts in spectral quality that directly impact yield. I've discussed this in-depth before, but it bears repeating: advanced measurement tools and regular lamp replacements based on time intervals are key to ensuring optimum lamp performance and keeping yields within a range of certainty.

Time as Your Indicator

A significant advantage of HPS lamps has always been their longevity—they reliably deliver consistent output for about two years. Beyond that two-year mark, even the best-quality bulbs experience notable performance drops. Our ongoing lab research involves monitoring lamps from several manufacturers across multiple quality grades, precisely tracking how output intensity and spectral quality decline over time.

The findings consistently reinforce the agronomic imperative to replace lamps regularly at the two-year threshold. We have observed a non-linear relationship between PPFD loss and yield, 8.3% and 30%, respectively. You can check out a deep dive on that here.

What Does This Mean For You?

Simply put, know your lamps' age. Regular replacement isn't just about maintaining crop yield—it's about protecting your margins.

To put this into perspective clearly, I've included an easy-to-follow chart demonstrating when replacement becomes financially imperative:

• At 0-10% loss: You might not feel the pinch immediately, but it's there. There is a natural lumen drop-off after the first cycle, which you can see clearly in the spec sheets. But we know that Lumens are for Humans!  

• At 20% loss and beyond: Replacement not only pays for itself but becomes essential to avoid profit erosion.

Yield losses beyond 20% rapidly become financially unsustainable, making lamp replacement not just sustainable agronomy but an essential business practice. Double-Ended HPS have a much longer life than their predecessors and a strong plateau after that “First Crop Pop”. However after the 10K hr mark (less with lower quality lamps), the rate of yield drops off significantly, not only due to the loss of PPFD on canopy, but also the quality of the spectrum shifts out to the right, reducing blue and increasing Red and Far Red, throwing out critical ratios for productive application. 

As HPS lamps degrade, the energy shifts further to the right, throwing off the critical Red to Blue Ratio (that is best out of the box), Red to Far-Red Ratio (Known to effect morphology and quality), and off the scale of this chart: more IR heat emission which effects VPD and system efficiency. This decay is just from the stability of the plasma reaction getting looser and less able to hold the high energy (Blue) where it needs to be. Lower quality lamps have fewer safeguards in them, and this shift will happen quicker.

As always, stay proactive, track your lamp usage, and plan. Regularly replacing your lamps at that critical two-year milestone safeguards both your yield and your profitability.