im having a hard time being able to tell if my new leaves on my plants are yellow or if my hps is making them appear yellow. when i take pics w my digital camera they dnt really look as yellow. i was thinking it might be the hps making the new growth look yellow since its thinner or something idk.
High-Pressure Sodium (HPS) lights
High-pressure sodium lights yield yellow lighting (2200 K) and have a very poor color rendering index of 22. They are used for the second (or reproductive) phase of the growth. If high-pressure sodium lights are used for the vegetative phase, plants will usually grow slightly more quickly. The major drawback to growing under high-pressure sodium alone is that the plants tend to be taller and leggier, with a longer internodal length than plants grown under metal halide bulbs. High-pressure sodium lights enhance the fruiting and flowering process in plants. Plants use the orange/red spectrum HPS in their reproductive processes, which produces larger harvests of higher quality herbs, vegetables, fruits or flowers. Sometimes the plants grown under these lights do not appear healthy due to the poor color rendering of high-pressure sodium, which makes the plants look pale, washed out or nitrogen starved.
High-pressure sodium lights have a long usable bulb life and six times more light output per watt of energy consumed than a standard incandescent grow light. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally, these lights are the preferred supplemental greenhouse lights. But, in the higher latitudes, there are periods of the year where sunlight is scarce, and additional sources of light are indicated for proper growth. HPS lights may cause distinctive infrared and optical signatures, which can attract insects or other species of pests; these may in turn threaten the plants being grown. High-pressure sodium lights emit a lot of heat, which can cause leggier growth, although this can be controlled by using special air-cooled bulb reflectors or enclosures.
Hope this helps:
http://en.wikipedia.org/wiki/Grow_light
