Does reflectors change lumen output greatly?

[Schu338]

I have (11) 2 x 4 (6)-lamp 32w t-8 fixtures in my shop I am converting to LED (removing ballasts). The POCO rebate is giving me back about 70% of the lamp cost. That plus the wattage savings make it a no-brainer. The fixtures have the polished reflectors installed, and mounting height is about 13'.

Since the lumen output per bulb is approx the same (2500), do you guys think light level be same, less, or greater?

If led's are a 120--degree spread, would the reflectors even make a difference anymore?

I will measure footcandles before / after. Just looking for thoughts.

 

[nadogail]

Reflectors have no influence on Lumen Output, Just as Drag Racing Slicks have no influence on Horsepower.

Maybe they will have some influence on the Foot Candles measured at the work surface.

 

[cybrdyke]

Schu-
It might help you to understand beam angles. Your 32w fluorescents deliver light in a 360 degree shape. Some of that light is wasted inside the fixture as it never gets out of the fixture to get to the target. Assuming that you have good reflectors, and that they are clean, you will have lost about 15% of it. The ballast in your fixture is probably a high lumen 118% ballast, which greatly increases the lumens from the lamp. Your lamps are not brand new, so they probably have lost about 10% or so. Taking all of that into consideration, you are actually getting about 2575-ish lumens per tube out of your fixture. (2850 x 1.18 x .85 x .90)
So, a 6 lamp highbay actually only delivers about 11,500 lumens.
Your new lamps at 2500 lumens and a 120 beam will not use the reflectors anymore. 6 lamps, side by side, at 120 beam will come fairly close to mimic-ing the original fluorescents. It might be a slightly tighter beam, but not much.
You should notice that the light is slightly brighter when you do the install, but you'll get used to it pretty quickly.
Good luck,
CD

 

[Schu338]

Thanks. That's pretty much what I was thinking.

 

[AntonLargiader]

It's not all that significant, but wouldn't the reflector loss only apply to about half of the light? Or is that already accounted for in your 85% figure?

Schu-
It might help you to understand beam angles. Your 32w fluorescents deliver light in a 360 degree shape. Some of that light is wasted inside the fixture as it never gets out of the fixture to get to the target. Assuming that you have good reflectors, and that they are clean, you will have lost about 15% of it. The ballast in your fixture is probably a high lumen 118% ballast, which greatly increases the lumens from the lamp. Your lamps are not brand new, so they probably have lost about 10% or so. Taking all of that into consideration, you are actually getting about 2575-ish lumens per tube out of your fixture. (2850 x 1.18 x .85 x .90)
So, a 6 lamp highbay actually only delivers about 11,500 lumens....

 

[cybrdyke]

It's not all that significant, but wouldn't the reflector loss only apply to about half of the light? Or is that already accounted for in your 85% figure?

Good question. Its already accounted for. Without specific fixture information, I have to assume that it's a common generic 6 lamp T8 highbay. Alot of these have highly reflective silver reflectors, which I believe the OP is talking about. Those reflectors are pretty helpful when used with fluorescent lamps. Without them, the fixture would be about 75% efficient. With premium ones, it can go as high as 95%.
Using very crude figures for example:
Half of the light emitted from the lamp goes upward and bounces off the reflector, about 30% of that will never make it back out of the fixture. So, you get 70% delivered lumens from the top half of the lamp, and 100% delivered lumens from the bottom half, which is approx 85%. Again, this is a very crude example, but for this purpose it's OK.
Fixture efficiency is a specific, measured criteria that is reported on spec documents from manufacturers (well, the good ones anyway). It's less common now that LED's have taken over.
CD