LED Lighting Primer - Part 1 (Background)

Apparently the way my fathering nesting instinct kicks in is through home improvements, as I've had a brand new motivation to plow through a ton of things while at home for paternity leave. One of the large projects has been the conversion of the whole house to LED lighting.

I've learned a lot more about lighting in the process than I would have imagined, and writing it might be interesting to others.  Consider this a primer for the state of the world circa October 2014. And caveat reader, I am in no way an expert, but consider my self an enthusiastic amateur.

Note: I'm going to do this as a multi part blog post, because this is going to be long. Hopefully you'll find the section you are interested in and pick out what's useful to you.

Light Bulb Shapes and Sizes

Before diving in it's worth talking about light bulb shapes and sizes, because, honestly, this confused me for a long time.

The code number of a bulb consists of a letter or letters followed by a number. The letter indicates the shape of the bulb and the number relates to the diameter of the bulb in eighths of an inch. The mosts commonly used household bulb is the A-19. The bulb is "A" type and the diameter would be 23/8". A 65BR40 is a 65 watt reflector 5" in diameter.



In addition to the shapes of bulbs, there is a whole orthogonal matrix  which is the base sizes.


Again these are coded with a shape and a diameter. However the diameter for bases is measured in millimeters. So you need metric and imperial units, on the same bulb, to categorize it. I'm sure there is a story behind it, and I'm sure it's crazy.

While that looks overwhelming the reality is for house hold use you are looking at only a few of these.

Base Sizes you probably have:

  • E26 - regular screw base light bulbs (E stands for Edison btw)
  • E12 - small screw light bulbs. Aka candelabra bulbs.
  • T8/T12 - tube florescent lights

Bulb shapes you probably have:

  • A19 - this is the regular 60W incandescent bulb. Yes, you can still buy these.
  • A15 - this is often the shape used for appliances (refridgerators).
  • PAR20 / PAR30 - if you have track lights
  • R20 - I've got this in my range hood, not sure it's other users
  • T8 / T12 - if you have tube lights
  • C7 - this is the standard Christmas light string bulb

The reason this is important is that lighting fixtures have a design point of the bulb going into them, and you'd be surprised how close those tolerances are some times.

Measuring Light

It's kind of amazing that for the first century of electric lighting we measured the light of bulbs by the amount of energy they consumed. Given that incandescent bulbs turn 90% of their energy into heat (not light) maybe it's not so odd. But it tells you very little about what this is going to look like in your home.

The lighting market was so static for so long we could get away with 60W as measure of brightness. CFLs made that more difficult, so everything has markings about the "equivalence". So a 17W CFL is a 60W equivalent bulb. But with LEDs landing everywhere now the industry is fortunately taking a step back and actually starting to use some real measurements so you can compare things.

There are two critical dimensions of light: color and intensity.


Color is measured by temperature in Kelvins. It's based on the physics of black body radiation, and largely moves between a red and blue scale. Computer monitors have been using color temperature for enough years now that people are hopefully a little familiar with it.

Black body.svg
"Black body" by Darth Kule - Own work. Licensed under Public domain via Wikimedia Commons.

Incandescent bulbs typically are 2700K - 3300K in color. Soft white or Warm white is often how it's referred to in lighting. Daylight is closer to 6000K and is what's considered Cool white. If you like your light slightly yellow, stick to the low end here (2700K).


Intensity is measured in it's own standard unit of Lumens, which is actually a perception unit, so it does attempt to compensate for only what your eye reacts to. The whole process of calculating lumens is pretty complicated, so don't expect to work your way through it. It's a unit of measure you'll just have to build new intuition on.

Leaning back on our crutch of "this is what incandecants are like", here is a handy chart courtesy of Clark Howard:

How Much Light Do I Need?
Incandescent Bulbs


Minimum Light Output


40 450
60 800
75 >1,100
100 1,600
150 2,600

Why LED?

LEDs have a bunch of advantages. Honestly, the wikipedia page on LEDs is fun reading if you want the full history.

The top reasons for me were:

  • Energy efficiency: uses about 1/6 the power of equiv incandescent and 70% the power of florescent. This also means less load the electrical in your house.
  • Cool to the touch: you can tell you are't wasting energy because you can touch the bulbs when on and they are only slightly above room temp. Important for certain applications.
  • Longevity: LEDs are rated for roughly 20 years of use before failure. And it's pretty clear that's probably a low ball number. Also failure in LED case is typically they get dimmer by 10%. These are heritage items that might be passed down to your kids or grand kids. Which also means they are not going to generate landfill. Which also also means you don't need a shelf full of spares around.
  • Near instant on: no delayed ramp up to full intensity like CFLs.
  • No humming: I can hear the CFL ballast humming (though apparently my wife doesn't notice it). The new silence in our master bathroom was astounding.

The other great thing about LEDs is the actual light unit is this little chip. So while you can get LED light bulbs that retro fit existing fixtures, you can also get fully integrated light fixtures in shapes and sizes that have never been possible before. That's a lot more extensive than just changing out bulbs, but it opens up a lot of possibilities (more thoughts on that later).

The whole series:

As always, corrections or comments welcomed in the comments here.