i have been doing some research and gained pretty good insight to how lighting works. i feel everyone should be able to understand what the units mean on the light bulbs. such as when a light bulb lists 40 watts 2650 lumens and 5000k. most ppl dunno what the hell that all means. many ppl even think 5000k bc of the kelvin is related to temp when its really related to colour. so if your one of them who wanna understand the world of light and how it reflects upon marijuana growing keep reading. first off lets start out with lumens. everyone knows the more lumens the better. this is true. so for example my in particular HPS is 400w with 40000 lumens. thats good. so you get the idea. next lets move onto wattage. wattage and volts are not related like you would relate grams to pounds. wattage is the amount of energy used. a volt is the amount of electric potential. so in laymans terms a volt is the amount of capable energy. now we have the light spectrum which is how u can interpret kelvins with their appropriate light band. so most of us know that there are two light cycles. one for veg growth and one for flowing. there also are different light spectrum's that influence growth patterns. these colour bands are attributed to a degree of kelvin. so when you read 5000k or kelvin what you should be saying to your self is "oh, 5000k is equal to daylight. this is good for veg/flowing" now comes the difference between vegetating and flowering. veg growth is prompted by higher amounts of Kelvin. aprox 6500 is ideal this is the Blue band. Flowering is influenced by lower lights such as 2700 being aprox. this is the Red band. this information i hope helps everyone when looking at bulbs. this can be very helpful for choosing CFLs which is what brought me to do my research. sources: http://van.physics.uiuc.edu/qa/listing.php?id=2332 http://www.rollitup.org/newbie-centr...olor-temp.html