10 Ways to Ensure High Yields and Crop Productivity with your HPS Luminaires

James Grouzos

Growing Advice, Light Maintenance, Lighting Strategies, Maintenance | October 1, 2021

Lighting is perhaps one of the most important aspects of growing a crop, and just as you would spend money and time to upkeep a car to ensure it runs properly, a lighting system needs to also be maintained for you to get the most out of it.  Grow lights need to be cleaned, re-lamped and tested to ensure they are still working well.  If not, you can run into problems such as slowed crop growth, increased crop cycles, and overall loss in crop productivity which can lead to lost profits.  In this article, we go over 10 ways to keep your luminaires maintained so you continue to have optimum PAR output while ensuring high crop yields and peak efficiency.

1.Keep a re-lamping schedule.  Lamps used in horticultural lighting do not “burn out” like household lamps and need to be replaced after so many hours of use.  As you can see from the chart below, light output diminishes after every 1000 hours of use with HPS lamps.  We recommend re-lamping after 10,000 hours of use, which may be anywhere from 2-5 years depending on how often you use your lights.  It is important to note that every 1% loss in light equals to a 1% percent loss in production – so as you can see after 10,000 hours of use, your light output has diminished by 7-8%.  For CMH or MH lamps that interval is even earlier, and they need to be replaced at around 8000 hours. Decreased lamp output is even more pronounced in sole source indoor applications, where there is no natural sunlight to offset the associated depreciation in light.  These growers may see a greater loss in crop productivity as they go over 10,000 burning hours.

Note: Chart above is for example only. Lamp depreciation rates may vary by manufacturer—refer to specification data sheet for actual depreciation rate of any given lamp

Based on your hours of use each year, we recommend making a re-lamping schedule, so you don’t forget to purchase lamps for when you need them. Below we have created a chart showing approximately when to re-lamp your HPS and/or MH/CMH luminaires based on crop type.  Additionally, when you are re-lamping, make sure that your lamps are installed correctly.  If they are not installed properly, you can experience lamp failure.  Refer to our video on how to install a double-ended lamp for further guidance.

2. Check your light output using a light meter to see how much light you are really getting.  This can be done after 2-3 years of luminaire use.  We recommend the use of a quantum-sensor (PAR-sensor) for the measurement.  To get a measurement, stand in the middle between 4 (four) luminaires, as you would see on your light plan, and take measurements at the crop level.  Take note if there are any shadows, objects or anything that might interfere with the reading.  You can also ask one of our sales managers to come by and assist with measurements if things are unclear or if you have problems.  Something to also be aware of is to make sure your light meter is calibrated.  Just like other equipment (a pH meter, for example), a light meter also needs to be calibrated to ensure accurate readings.  Refer to your light sensor manual on how to calibrate.  

3. Look for consistency in your lighting.  What we mean by this, is do all the lamps look to be the same in light output when you look up at them, or do some look dimmer than others?  If so, this may mean that you need to re-lamp.  Having uneven light output will affect growth and yields.

4. Clean your reflectors every year.  Reflectors can become dirty with dust and grime, which can reduce light output by up to 10%.  A simple way to increase your light output is to clean them with a simple vinegar and water solution. The best time to do this is in the summer when you are not using your luminaires.  Refer to our maintenance video for more info.

5. Remember to dust off and clean your outdoor K-LUX, or other outdoor light sensors.  These sensors are designed to tell you when natural sunset and sunrise are, so your climate software knows when to turn on or off your lights.  If they are dusty or dirty, they may be getting faulty readings and your luminaires may be turning on unnecessarily early and wasting light when you don’t need it.

6. Remember to clean shade compounds.  If you are using white washing or other shade compounds on your greenhouse, be sure to have it cleaned when you start to use your lights.  Whitewash actually blocks a lot of blue wavelengths, which can result in plants stretching more as the red/far-red wavelengths will be more prominent in the greenhouse, which can activate a stretching and shade avoidance response.

7. Are your capacitors working? If you are still using older magnetic ballast technology, ensure your capacitors are working.  If you have bad capacitors, you might experience lighting failure when re-lamping.  Since this old magnetic technology is fast becoming obsolete, replacement capacitors are becoming extremely difficult to find, so we strongly recommend you consider upgrading your lighting system to high-efficiency electronic ballast or LED luminaires.

8. Follow the light plan. To keep your lighting uniform, make sure that your luminaires are installed according to the light plan.  Also, make sure that luminaires are all on the same plane when installing – having some placed higher and some lower will result in lower light uniformity and can adversely affect plant growth and yields.

It’s important to know that different manufacturers’ luminaires distribute light differently, and a light plan from one manufacturer will differ from the next.  You cannot simply swap out one luminaire with another and expect the same results.  We recommend always consulting with a professional lighting company and getting a light plan before any new luminaire installations, and always follow the light plan given.

9. Try changing the reflector. Do you want to get more light down deeper in the crop or want a wider field of illumination? An easy way to change the distribution of your HID luminaire, is to change the reflector.  We offer two kinds of reflectors, the Beta reflector which distributes light in a more deeply downward into the canopy, and the Alpha reflector, which distributes light in a wider illumination field.

10. Order early! If you need new lamps or other replacement parts, we recommend ordering as early as possible.  This ensures you get the parts when you need them, and you are not rushing last minute to try and get what you want.