I'll try tohelp a bit with the 'confusion'.
Grow yield (NOT pr. plant yield) highly depends on 3 factors:
Energy - Light intencity
Buildingmaterial - nutirents
Genetics - strain
These 3 factors ar the most important once considering yield. The most important one in yield consideration is the energy.When you grow outdoors, mother sun takes care of the energy, outdoors growers only have to think about the two other factors. I'm ONLY talking about indoor growing here.
The trick about light is that the light energy that the plants can actually use, gets weaker by a factor of 4 when doubling the distance. The light energy available to plants 2 feet from your lights will bee 1/4 the light energy available at 1 feet from the lights. Thats why it is so important to keep your light close the where it's needed - at your plants. Thats also why it is yield wise favorable to use a growing technique where the plants are evenly heightet like SeaOfGreen (SOG) or ScReenOfGreen (SROG/SCROG). While were at it, let me also try to explain why you cant really ask/answer how much yield you can expect from ONE plant. The amount of buds produced depends on how much of the lights energy you succeseed to make available for bud production. So depending on strain and growing technique, the amount of energy available for bud production can be very different (density of the plants foliage and overall distance from light to foliage). Growing one big plant with a light hanging at the top as a star on a christmas tree is actually a stupid way of utilizing the light energy, cause only the top branch gets the full benefit of the short foliage to light distance. Thats why most comercial growers use som kind of technique to average the height of the plants to make the foliage to light distance more even, so that as big as possible amount of the light energy gets used to produce the mighty weed
Also, nearly all light penetrating the plant foliageand hitting the soil, wall or container is more or less useless.Therefore, keep your pleants as tight together aspossible, while also giving the plants room for growth. This is one of the key factors for increasing yeild - to maximise the amount of light that hits your plants foliage directly, and to make distance to lights as close as possible without burning them.
The ONLY measurement of interest when talking about indoor yield is weight of final smokeable product pr.watt, usually grams/watt. This is because the money for the energy (and therefore energy for your plants) is the number one, top of the list expence when growing indoor.
Don't expect more than 1 gram/watt... EVER!
As a firs time grower, you should be happy and satisfied (and congratulate your self) if your harvest ticks in at 0.5 gram/watt.
NOTE: There are myriads of other factors that affects yield, all of witch you will probably slowly learn to master, harvest by harvest, as you see your yield aproach 1 gram/watt (when talking grams/watt it is nearly allways when using HID lightning at 250 watt pr. bulb or more. Anything less that
HID@250 watt is not considered economically attractive).