Objective  Effects of laser and light-emitting diode (LED) exposures on growth, photosynthesis, and physiological and biochemical characteristics of Solanum lycopersicum seedlings were investigated.

  Method  A CIRAS-3 system was used to determine the photosynthetic response of 30-d-old tomato seedlings exposed to 2 red and 1 blue monochromatic laser or LED. Then, using a color temperature of 6 000 K white LED as control the seedling growth under the LED white light supplemented with a small amount of blue light along with the photosynthesis-stimulating red light as treatments was compared.

  Result  The photosynthetic capacity of the seedlings exposed to 650nm red light was greater than the other wavelengths of red light when the photosynthetic quantum flux density PPFD was below 400 μmol·m⁻²·s⁻¹. The capacities produced by laser of 650 nm and 450 nm were greater than LED of same wavelengths. The growth indicators, maximum net photosynthetic rate, and water use efficiency of the seedlings exposed to either laser or LED was greater than control, but laser significantly higher than LED (p＜0.05). All treatments had a same light compensation point, but the seedlings grown under white LED supplemented with both 650 nm and 450 nm laser had the lowest light saturation point. In addition, laser was significantly more effective than LED in increasing the contents of chlorophyll a, carotenoid, and malondialdehyde (MDA) and the activity of peroxidase (POD), although it did not affect the superoxide dismutase (SOD) activity.

  Conclusion  The white LED supplemented with laser, especially both 650nm and 450nm, significantly promoted the growth, photosynthetic capacity, and antioxidant activities of the tomato seedlings in comparison to LED supplementation.