[Brandon Holley]

Originally Posted by pfreivald

I know, but all that really tells me is that a lumen rating is a poor indicator of how a bulb 'looks' in a room...

This is an extremely true statement. While lumens are an important metric when evaluating light, there are often many other factors to consider.

When dealing with LED bulbs in particular, higher CCTs (color temperatures) result in a higher light output (for the same drive current). Essentially, higher CCT LEDs are more efficient than lower CCT LEDs because the phosphor conversion of blue light to white light is less dramatic.

Many companies will try and squeak a few more LPW (lumens per watt; essentially how efficient the bulb is) out of their fixtures and bulbs by bumping the CCT up a little bit and essentially gaining free light.

CRI (color rendering index) is another very important measure, albeit a controversial one at times. CRI basically tells you how well the light coming out of the bulb/fixture renders colors. The higher the CRI (max=100) the closer it is to natural sunlight in terms of color rendering. You can read more about CRI here: http://en.wikipedia.org/wiki/Color_rendering_index

One last measure which has a lot of play in LED lighting is lux. Lux is a measure of ILLUMINANCE, not LUMINANCE. Lux takes into account how much light is being emitted over a certain area. In situations which are a direct replacement for incandescent or flourescent bulbs (such as the FIRST bulb) it is not as useful, but for other LED retrofitting applications it is extremely useful. One example of where lux is extremely important is in streetlighting. Streetlighting has very specific requirements for lamps to meet so roads/sidewalks/parking lots are lit correctly. Just putting a big light source in a fixture will not necessarily give you the correct light output. To ensure the beam is being spread and shaped correctly, measuring lux at specific areas of illuminance will tell a better story of how well the light fixture is working.

These are some more metrics that can be useful when evaluating light, and LED lights in particular. As with most things, there are direct tradeoffs between things like cost and efficiency, CRI and output, etc. It is our job as engineers to find a balance that consumers will enjoy!

-Brando