The simple answer is YES, if you have a high enough light intensity. The key to a healthy bloom and good yield is having the right level of PAR (photosynthetically active radiation) light for the type of plant you are growing. The standard way to measure PAR light is in micro-moles per square meter per second (µmoles/m2/s.) On a sunny day at noon in Missouri, the sun delivers around 2,000 µmoles/m2/s. Different plants require different levels of light for healthy flowering. For example, lettuce and potatoes can grow under only a few hundred µmoles/m2/s. Red peppers require higher levels and tomatoes need light levels 1,000 µmoles/m2/s or higher. Too much light does not necessarily help: Plants only absorb a certain maximum level of light and the rest is reflected back. This maximum level is called the “light saturation point” and it varies from plant to plant. In order to achieve good flowering, the leaves of your plants need to receive PAR light levels that approach their light saturation point.
Well designed LEDs lights concentrate their emitted light in the deep blue and deep red part of the light spectrum where absorption by plants is highest. Thus, LEDs allow you to achieve good bloom with a lower PAR light value compared to HID lights. If the LEDs are delivering light in the right parts of the spectrum (deep blue 430-460nm and deep red 650-670nm) where absorption is at its maximum, the PAR value required for bloom can be 40-50% below that of HID type lights.
Many Chinese made LED grow lights use low power one or two watt LEDs with common colors used for traffic lights etc.. not well suited for horticulture. Companies importing and marketing these lights make all kinds of claims about results and show pictures of various types of plants growing as proof. Just because you can grow lettuce under UFO type lights does not mean you will get tomatoes to bloom.
We use the latest 3 watt LEDs which are the most efficient single die LEDs on the market. The light is concentrated in the right parts of the light spectrum deep blue (430-460nm) and deep red (650-670nm) where absorption is highest and deliver PAR light levels that are at or above the light saturation point of the most demanding plants. This produces excellent results in flowering when the light is positioned 18″ to 24″ from the plant canopy.