170915-1130 EDT
What I am trying to do is analyze from basics.
Tape and rope LEDs for 12v use parallel strings of three LED elements + resistor in series spread over a large physical distance. Each string can be made of three LED packages and a SMD resistor or it could be a three chip package and less obvious resistance trace. LEDs possess an NTC characteristics and parallel driven elements that are not thermally bonded together causes current to accumulate towards the hottest string hence ballasting of individual strong.
The commutation behavior as seen from the line can be different from a long, single series string. For 120v mains circuit, there can be 40-48 in series, and for 240v, 80 to 96. As you get closer to edging Vf to Vpk, things change. There is a general region where linear ballasted LEDs operate in constant BF, variable BEF mode where ballast dissipation is a function of line voltage.
This post does not take side in favor of or against the lamp type used for converting electrical current into light, although i am discussing the effect on light quality and luminous efficacy from ballast implementation that are designed around manufacturing cost interest.
Linear ballast works by burning off energy in the process
A design implementation like this primarily benefits to widen the gap between consumer price and cents of variable cost per final product.
www.onsemi.com/pub_link/Collateral/DN05013-D.PDF
There are few references in there pitching superiority to fluorescent. it omits notably inferior light quality due to presence of extreme flicker. how convenient right? This is not LED vs fluorescent. It comes to LEDs being able to run from a crude ballasting circuit that can have abysmal efficiency and terrible light quality.
To manage flicker, it is necessary to store energy in the phosphor, thermally or in the drive circuit. Incandecents and HIDs do so thermally. Fluorescent do so in the phosphor and drive circuit. An entirely solid state circuit together with LEDs is a recipe for extreme flicker.
A decent LED ballast is based on the same design as a good fluorescent ballast and provides the same benefit like good line maintained efficiency over line variation and low flicker. The ballast is a significant part of fluorescent system cost. A crude LED ballast can present an appearance that LEDs are economical without providing the same performance. Omitting capacitor and letting a lot of flicker spew out is an easy way out of having to deal with thermal vulnerability of capacitor in integral ballast.
CEC T20 and T24 are leaping ahead in recognizing flicker issues, but for those outside of California Energy Star basically have no restrictions on flicker. Influence of line voltage variation, flicker index and flicker percentage are those that requires particular attention.
