HID bulbs are high-intensity-discharge bulbs. These bulbs are designed to produce more light than incandescent grow lights. According to the website Home Harvest Garden Supply, HID grow lights can provide 500 percent more light than incandescent grow lights. The result is that plants grown under HID lights are healthier and stronger. But bad HID lamps can harm a plant more than help it. Bad HID bulbs have distinctive signs.
Poor Plant Growth
As an HID bulb begins to decline in quality, it will start to put out less light. Plants grown under these lights will no longer be able to thrive. Instead, they will look much like plants that are grown in a window. Plant growth may become weak, leggy or spindly. Additionally, plants may begin to bend toward the strongest nearby light source as they grow. These are all signs that it may be time to replace your HID lighting tubes.
Changing Tube Color
Metal Halide HID bulbs and High Pressure Sodium Lamps both contain sodium. As time wears on, the sodium dissipates from these lamps. As the sodium dissipates from a lamp, the bulb may change color. Some HID lamps turn bluish in color. Others exhibit a pink tinge and flicker as they turn on. Plants may become leggy under this light because the HID lamps are no longer emitting light along the color spectrum the plant needs to thrive.
Some lamps, such as a mercury lamp will continue to work even after they have deteriorated. The only sign that the lamp may no longer be working well is a set of burns in the electrodes at the ends of the lamps. To check the lamp for these burns, turn the light off and slip the lamp's electrodes out of the ends of the HID fixture. The ends may appear blackened.
As high-pressure sodium lamps begin to deteriorate, they will flicker as they come on. This is because the aging bulb needs more voltage than the ballast in the fixture can provide to stabilize it. The flickering occurs when the ballast attempts to ignite the sodium vapors in the bulb. If the light does not come on, the ballast allows the bulb to cool before trying again.