LED vs T8's

[spark master]

Did anyone ever amp probe a 2x4 T8 4x32w, against an equal 2x4 LED, with similar lumens ?

I was just messing around at lunch time, and the amp difference was not all that much. I was not overly impressed with the amp reduction. Maybe the ballast and bulbs won't need replacing as often, but I'm not so sure about the energy savings..... New construction, yes, but to retrofit T8's and go through the expense... is it really worth it ??

 

[Electric-Light]

Did anyone ever amp probe a 2x4 T8 4x32w, against an equal 2x4 LED, with similar lumens ?

I was just messing around at lunch time, and the amp difference was not all that much. I was not overly impressed with the amp reduction. Maybe the ballast and bulbs won't need replacing as often, but I'm not so sure about the energy savings..... New construction, yes, but to retrofit T8's and go through the expense... is it really worth it ??

Factors that affect the total efficacy of a T8 system is in this order:

------Fixture reflectors and optics
---Lamps
--Ballast (assuming it's an electronic)

The most efficient T8 fixture can hit 90% and provide a fixture level efficacy close to 90 lm/W. For example.. specular reflector high bays. For indoor ones, best ones are usually in high 80s. Old ones are routinely 50-70%.

A drastic reduction like going from 4 x F40T12 magnetic ballast system to 2 x F32T8 is made possible when going from very inefficient troffers with F40T12 to 85% efficiency fixture with 3,100 RE80 lamps and matching the mean lumen or getting slightly below it.

If one goes directly to LEDs, the symptom of increased efficiency is often misdiagnosed as having been caused by LEDs, but it's really not correct.

Now, when you have a 12mpg approaching end of life, a replacement to 25 mpg vehicle is a no brainer.

With the latest and highest performance LED, it may get you say 28 mpg, but the added cost is hard to recover.

Scrapping your current 25 mpg with 60% life left solely to buy 28 mpg one to save on gas...?
You may save on gas, but remember that the upgrade cost a lot of money and you may never get out of being upside down.


Troffers designed on 1950s and 1960s template do not employ computer aided drawing and precision crafted reflectors with high efficiency in mind. The smaller size of T8 lamps does allow for somewhat more efficient optics given the same fixture depth allowance and even more so for T5.

F54T5HOs are less efficient at lamp/ballast level, but it makes up for it in some applications through a high fixture efficiency. 3 and 4 lamp, especially 3 lamp T8 troffers are not very efficient. Under the right conditions, one F54T5HO can replace a 3 lamp T8. (cheapest 700 series lamp with 2600 mean lm x 0.88BF x 3 lamps x 60%) =4,200 lm vs (4800 mean lm x 1.0 x 85% eff ) =4080 lm

But the biggest trick to the magic is that existing fixture must have poor efficiency. If they have a <10 year old electronic ballast, recently wiped down and freshly loaded 28W RE80 lamps, there's hardly a benefit in early retirement.

 

[Electric-Light]

As a rule of thumb, T8 ballasts are so close to 1.0 PF that you can use V x A = watts and I would give 55-60W for 2 lamper and 105-110W for single ballast 4 lamper.

0.5A/0.22A for 2 lamp ( 120/277)
0.92A/0.4A for 4 lamp.

You may want to make a 10 turn loop to multiply the reading by 10 if your clamp meter is too coarse relative to what the ballast draws.


The efficiency gain on the ballast is focused on 1 and 2 lamper. The difference in ballast efficiency for the 4 lamp ballast in the past 15 years is so little that its not worth a mention.

Ballast bypass TLEDs do have limited applications. If the existing ballasts are old and reaching their EOL (8-10 years in 16hrs/day retail use), fixtures are a wreck(dull, faded and peeling white paint) or they're not a good fit for the area to begin with(strip lights under trusses with a lot of light wasted in lighting up the under side of roof), they can work well. They seem as bright with half the power, because the crappy fixtures were wasting a lot of light.

They perform poorly if the existing fixtures didn't suck.

 

[hbendillo]

Depends on the LED fixture in question but indeed the savings can be as little as 10 to 15 watts per fixture. If you use an LED Basket type 2X4 that has a center louver and some indirect lighting optics they are not very efficient. If you use an acrylic lens type LED replacement that has the two linear LED arrays running down each side of the fixture then those are very efficient but produce a lot of glare. LED manufacturers tried to sell the idea of delivered lumens and apparent brightness but when you perform lighting calcs, the footcandles are not there. If you have to meet strict guidelines for footcandle levels the energy savings are not as dramatic as you might think.

 

[Electric-Light]

Depends on the LED fixture in question but indeed the savings can be as little as 10 to 15 watts per fixture.

It depends on what's being replaced and what you're comparing. If the area is over lit already, a wattage reduction that also accompanies output reduction should not be credited to "LED technology".

Please refer to my other thread here for some examples comparing essentially identical lensed wrap-around T8 vs LED. http://forums.mikeholt.com/showthread.php?t=170042

I ignored LDD (luminaire dirt depreciation) for BOTH, but factored in permanent lamp degradation. Basically, this is "tolerance formation" to electricity and produce less light per watt as they degrade. One version of LED here is predicted to degrade 30% over 50,000 hours of use. Other than metal halide lamps, LEDs in generally have THE HIGHEST lamp output degradation of all lamps. LEDs have been on the market for a while with minimal margin to penetrate the market and if you pay attention, you'll see that some LED products are starting to slip in performance and rising in prices.

LED manufacturers tried to sell the idea of delivered lumens and apparent brightness but when you perform lighting calcs, the footcandles are not there. If you have to meet strict guidelines for footcandle levels the energy savings are not as dramatic as you might think.

My comparisons are based on delivered lumens. Footcandle levels are hard to compare. You really should have a graphical view along with values. You could easily get a higher floor surface FC by messing with the reflector. It's like playing with the settings on a shower head.

Take a look at this picture:
Yo could easily put some reflective wings on the sides of the fixtures to squeeze the light and increase the FC level landing on a 2 1/2 ft high desk setup on the floor, but this comes at the expense of reduced light level on the upper shelves. What you really want is a distribution pattern that maintains the same light level from bottom shelves to top shelves.

https://www.lightingdesignlab.com/sites/default/files/pdf/Design-Guide-T5-High-Output-Warehouse.pdf

Fluorescent fixtures are available in a several different beam width. Changing the beam width changes FC level at different surfaces. If you currently have wide distribution fixtures and the current building use is better served by a narrow distribution, you can realize savings by replacing them with narrower distribution fixtures.

What about uniformity?
A checkered flag consisting of 100% black+100% white or colored 50% black evenly around will both give you the averagedarkness of "50% black". I could also state that the checkered flag has twice the peak whiteness which is like the "maximum FC level" expression used in LED sales talk. If the pattern is anymore complex, a computer aided visual representation is needed.

LEDs are not BETTER. It's more suitable in some applications just like properly fitted square pegs are better than a round peg sized to fit in it.