Commercial LED Lighting: Converting to LED
By Scott DeGaro, LEED AP BD+C, O+M
Donald asks: I’m looking to possibly convert a commercial property of mine to LED lighting, however I have a concern that if i convert to commercial LED lighting, the new lighting will not be as bright, since my existing lighting is T8 34W (rated 3200 lumens) and the LED bulbs I’m looking at is only 1600 lumens. Could you speak a little about this? Would the lumens be a direct apples-apples comparison?
Thanks for the question, Donald. If I understand your question correctly, there’s actually two main considerations and questions that are really involved.
First there’s the direct question of 3,200 lumens compared to 1,600 lumens. Second, from an owner’s perspective would be the costs involved in making the switch.
My understanding is that T8 lamps are standard at 32W and T12 lamps are available in standard 34W lamps. For the purposes of this discussion I’m going to assume that you’re existing fixtures use 32W T8 lamps. For clarity and consistency I’m basing this entire discussion on each fixture consisting of two 4-foot lamps and a single ballast. There are many other sizes and configurations that can affect your lighting, such as parabolic vs. lensed fixtures, ballast efficiency which will have to be evaluated for your specific situation.
It sounds from your question that you’re planning on simply replacing the existing T8 bulbs with LED replacement “bulbs” that will fit the same fixture. This is a great method to make the switch, but there is your obvious concern of the resulting brightness, which I’ll discuss later.
You’re obviously interested in the fact that your current T8 fixtures use about 62W of power (including the ballast input) with a 20,000 to 30,000 hour average life, while LED replacement lamps would only use 30W of power but last for over 50,000 hours. There’s obvious cost savings due to direct electricity usage, but there’s also the savings from not having to replace lamps and ballasts as frequently, which we’ll also discuss later.
I’m sure you’ve already discovered the good news, that many manufacturers produce an LED “bulb” that matches the size a T8 lamp, while not having to replace the entire fixture. That obviously saves the cost and interruption of having to replace your existing fixtures with LED specific fixtures, but the existing ballasts will need to be removed or rewired. If you have another location, you can relocate the ballasts to that property as spares.
However, as you stated in your question there is the issue of lumens. ith the LED lamps having half the lumen output of the T8 lamps, there may be a decrease in the perceived brightness of lighting. Lumens are measured over the entire area of light generated by a lamp. For a T8 lamp the lumens are measured over a full 360-degree sphere wrapped around the lamp (i.e. a tube). Because LEDs typically focus their light in a given direction, even though they’re lower in lumens, the lighting may actually seem brighter because it’s spread over a smaller surface area. I think it’s best to evaluate the specific rooms on a case-by-case basis. This will allow the actual photometrics of each fixture to be evaluated based on room usage, while taking into consideration other sources of light such as natural daylight or task lighting. This is something that a lighting designer will be able to give you better information on, as well as review the specific photometric output files for each light fixture. For additional insights into this, see Dave’s answer on lumens per Watt for LED lighting.
Then there are the variety of costs that need to be considered regarding the switch. First there’s the actual cost of the materials and labor required to make the replacement.
LED T8 replacement “bulbs” cost approximately eight times the cost of 32W T8 lamps (approximately $80 vs. $10 each). You’ll have to add to this the cost of the labor to physically replace the “bulbs” and remove or rewire the ballasts. If the switch to LED “bulbs” requires additional fixtures to be installed, then this cost will also have to be added. This cost will have to be compared using life-cycle costing to the cost of keeping the existing lamps and replacing ballasts and lamps as they need. There are many resources available to help you out with that process if you need it.
It’s also important to keep in mind when selecting LED lamps that there are other factors that affect how the human high sees the light. The temperature and color of the light are important. The color of the LED lights can vary from manufacturer to manufacturer and even within the same batch of lamps. It’s important to get test results from the manufacturer regarding their lights to ensure a uniform and pleasing color of light. Once again this is something that a lighting designer can help you with.
This is one of those things that certainly should be evaluated in more detail for your specific situation.