Plant lamps are used for indoor horticulture, plant reproduction and food production, including indoor aquatic and aquatic plants. Although most plant lamps are used in industry, they can also be used at home.
According to the inverse square law, the intensity of light radiated by a point source (in this case a light bulb) reaching the surface is inversely proportional to the square of the distance from the source (if a pair is twice as far away, it receives only a quarter of the light) which is a serious obstacle for indoor growers, and many technologies are used to use light as efficiently as possible. Therefore, reflectors are often used for lighting to maximize light efficiency. Luminaires or lamps move as close as possible so that they have the same lighting, and all the light from the lamp falls on the plant rather than the surrounding area.
For example, incandescent lamp, fluorescent lamp, metal halide lamp (HID) and light emitting diode (LED). Today, the most widely used lamps are HID and fluorescent lamps. Indoor flower and vegetable growers usually use high-pressure sodium (HPS/SON) and metal halide (MH) HID lamps, but fluorescent lamps and LEDs replace metal halides because of their efficiency and economy.
Metal halide lamps are often used in the nutritional stage of plant growth because they emit more blue and ultraviolet radiation. With the introduction of ceramics metal halide lighting and full spectrum metal halide lighting, they are increasingly used as the exclusive light source for vegetative reproduction and growth stage. Blue spectra may induce greater nutritional responses in plants.
High-pressure sodium lamp is also used as a single light source throughout the nutritional and reproductive stages. Similarly, they can be used as corrections for full spectral illumination during reproductive stage. Red spectrum may trigger greater flowering response in plants. If high-pressure sodium lamp is used as nutritional period, plant growth will be faster.
In recent years, LED indoor growth lamps can produce light of specific wavelength. NASA has been testing to increase the efficiency of space food on the space station. The results showed that plants were affected by the light of red, green and blue parts of the visible spectrum.