When investing in a led grow light, look at PAR value (or PPFD) at the distance you want to keep your grow light from your plants.

PAR - photosynthetically active radiation

PAR in plants designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. Natural sunlight has a PAR value of 900-1500μMol/m2/s when the sun is directly overhead. For a grow light to be effective, it should have PAR values of 500-1500 μMol/m2/s

PPFD - Photosynthetic Photon Flux Density μMol/m2/s. It is the amount of PAR photons reaching your plant and is measured in micromoles per square metre per second (μMol/m2/s). This measures how good a grow light is for photosynthesis.

How much PPFD do plants need?
Between 600-900 PPFD: This is great for the flowering, fruiting, or budding stage of plants. Between 200 PPFD and 400 PPFD, plants growth rate potential crawls around 30 - 55% which is recommended for mother plants or young, weaker plants that need a light that's not super intense

Lumens measure how bright a light is for the human eye. It is measured in lux or foot candle. An 800 lumens bulb in a 400 sq ft room will be brighter to human eye compared to when the bulb is in a room that is 1500 sq ft

A full spectrum white light is more comfortable for your eyes. Most of the ones I own are 5000K, K is for Kelvin. 

Kelvin is the 'color temperature' when we talk about led lighting.   It used to describe the color temperature of a light source. This is the specification that gives a description of the warmth or coolness of a light source.

Kelvin Temperature in Lighting

When people talk about T5, T8, T12, this terms only indicates the size and shape of the light bulb, not how good the light is. 

If the grow light does not list this information, I don't even consider buying it.
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