Question on why HID is better then T5

Hello all, if you didn't notice this is my first post on this site. Anyways alot of people on the forum agree that HID lights are more efficient than Fluros but my question is why? Yes I know, lumens/per watt is higher in HID lights, but when I calculate the lumens/square foot ratio, T5 Fluro's always win.
For example:
A 3x3 space lit by a 400w HPS vs 4 55w 2' foot Compact T5 Fluros

400w = 56,000 Lumens/ 3x3 = 6,222 Lumens per square foot IF you were to hang the light right above the plant, but with HID lights you can't you must hang it atleast 2 feet above the plan so..... 6,222 Lumens/4 = 1555
So a 400w HPS system hung 2 feet above the canopy would yield 1555 Lumens/square foot.

4 55w 2' foot Compact T5 Fluros= 5,000 Lumens per bulb x 4= 20,000
20,000 Lumens/ 3x3 = 2,222 Lumens per square foot.

Anyone know something I don't know? A 400w HPS is out performed by a 220w T5 Fluro system when you measure the true lumens the plants receive.

MariGuy said:

A 3x3 space lit by a 400w HPS vs 4 55w 2' foot Compact T5 Fluros

400w = 56,000 Lumens/ 3x3 = 6,222 Lumens per square foot IF you were to hang the light right above the plant, but with HID lights you can't you must hang it atleast 2 feet above the plan so..... 6,222 Lumens/4 = 1555
So a 400w HPS system hung 2 feet above the canopy would yield 1555 Lumens/square foot.

Click to expand...

your physics is wrong. you don;t divide by the final 4 just because the light is 2 ft away. wish i had a pic, but imagine a cone of light coming from the bulb. when that cone has spread out to cover 4 ft then you have 6,222 lumens per square ft at whatever vertical distance that equals.

make sense?

Ya I understand now. Thanks for clarifying