Elite growers recognize the importance of balancing performance to cost, making an optimal HID (High Intensity Discharge) grow lamp replacement time frame a moving target for indoor and greenhouse growers.
With regular use grow lamps efficiency is lowered over time, meaning you are paying the same for electricity but getting less usable light for your plants. On the other hand, quality grow lamp replacements are not inexpensive.
When used as a sole source of crop lighting indoors, single end HID lamps like MH (Metal Halide) and HPS (High Pressure Sodium) are best replaced every 9-12 months.
DE (Double Ended) HID lamps are a newer technology and give brighter light for longer—they are also more expensive to replace, typically. To balance economy and performance, these lamps can be replaced every 12-18 months.
Note: the above suggestions re grow lamp replacements assume an average of 12 ON hours per 24 hour period, so running them 18-to 24 hours a day further decreases suggested time between replacement. Very frequent ON and OFFs may also reduce optimal working life further.
Did you know that besides losing light intensity, the actual color (light quality) may also begin to shift? This means that the lamp output is not performing as designed to do for optimal plant growth per watt of electricity being used.