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 maintenance also. 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 an overall loss in crop productivity which can lead to lost profits. In this article, P.L. Light Systems discusses 10 ways to keep your luminaires maintained so you continue to have optimum PAR output while ensuring high crop yields and peak efficiency.
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 a 1% loss in production – and after around 10,000 hours of use, your light output has diminished by 7-8%," the team with P.L. Light Systems says. 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. 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.
Check your light output using a light meter to see how much light you are really getting, which can be done after 2-3 years of luminaire use. It is recommended to use a quantum-sensor (PAR-sensor) for the measurement. To get a measurement, stand in the middle between 4 luminaires as you would see on your light plan, and take measurements at the crop level. Be careful that there are no shadows, objects, or anything else that might interfere with the reading. 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.
Look for consistency in your lighting. 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.
Clean your reflectors every year. Reflectors can become dirty with dust and grime, which can reduce light output by up to 10%. A way to increase your light output is to clean them with a simple vinegar and water solution, which can best be done in summer when you are not using your luminaires.
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.
Remember to clean shade compounds. If you are using whitewashing 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.
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. It can be a good idea to replace your capacitors or consider upgrading your lighting system to electronic ballasts or LED luminaires.
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 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 is 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. Consulting with a professional lighting company is always a good idea, as well as getting a light plan before any new luminaire installations, and always follow the light plan given.
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. P.Ll Light Systems offers two kinds of reflectors, the Beta reflector which distributes light more deeply down into the canopy, and the Alpha reflector, which distributes light in a wider illumination field.
Order early. If you need new lamps or other replacement parts, do so 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. 
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