Originally Posted by John McDonald
I know I want the soft or warm light, similar to the color of an incandescent bulb. What is the difference between leds with say 9 SMDs versus say 36 SMDs, other than the number? Do more SMDs mean more lumens?
Probably far more than you want to know about light, but ...
One of the difficulties is there are many different SMDs. SMD
stands for Surface Mounted Device. There are many different electronic components that are SMDs, one type is a LED. They are usually identified by a number, and different SMDs produce different amounts of light, different color temperatures, etc. The only way you can compare how much light a lamp will produce by the number of SMDs is if they are the same model. Otherwise, a 9 SMD lamp may produce more light than a 24 or 36. Since many suppliers do not include the model # of the SMD they use, it's tough to compare.
The best method of comparing light output is by looking for the Lumen
specification. That is the total light produced by the lamp. If you are purchasing a fixture that includes the lamp you may find the specification of light output is Lux.
describes the amount of light on a surface. The important point when comparing fixtures by Lux is distance & coverage area. Two fixtures with the same Lumen lamp may produce very different Lux because one spreads the light over a wider area. This is why a reading light (with a narrow beam) seems much brighter than a general area fixture with the same Lumen lamp.
If you are concerned about color, Warm White is the description most often used to compare to an incandescent lamp. The technical description for the color attributes of a lamp are complex, but an incandescent lamp produces a color temperature
of somewhere between 2800°K and 3200°K and a CRI of 100.
Color Temperature is given in degrees Kelvin (a scale that starts at absolute zero as 0°K and shifts from infrared to red through the visible spectrum to violet and beyond (a clear blue sky without the sun is around 20,000°K). A cool white fluorescent lamp produces light with a color temperature around 6000°K.
Basically, Color Temperature is a method of describing the color an object will radiate if it is heated until it glows. It is more technical than that, but a tungsten filament will actually be at the color temperature while other types of light sources "manufacture" the color without actually being at that temperature.
(Color Rendering Index) is a number between 1 & 100 with 100 being the equivalent of an incandescent lamp. As the number drops, the source produces light that does not render colored objects correctly. For example a Sodium Vapor lamp has a CRI of around 24. That is why your red vehicle and lips look black in the parking lot.
CRI specifications are rarely given for LED lamps, but most of them are pretty good. CFLs sometimes have very poor CRIs which is why there are complaints about "green" colors.
Again, far more than you asked for, but I'm a retired teacher & once I get started it is difficult to stop!