Bests & Worsts Reviews from Amazon

There are many dimmable LED bulbs that can be used in TRIAC-controlled light fixtures. But there is a very noticeable difference between LED and incandescent bulbs when they are dimmed: - As lower current, the incandescent bulb's filament becomes cooler. Its light shifts to more yellowish and then reddish at minimum power. (Ironically, RED is considered warmer than BLUE. Therefore a lower color temperature of 2200K is said to be WARMER than 2700K) - An LED does not change its wavelength when driven at lower current. As the LED bulb is dimmed down, its color temperature remains nearly unchanged. So the light appears 'cold' when compared to an dimmed incandescent bulb. The main attraction of this product (Philips 'Warm Glow' 60 Watt Equivalent Dimmable A19 LED Bulb) is that when it is dimmed down, its color temperature actually shifts lower from 2700K to 2200K. This makes the bulb appear more yellowish, closer to what happens to an incandescent bulb when dimmed. How does Philips do it? My engineering guess is that there are two banks of LEDs inside. At full power most of light comes from the 2700K bank. As the bulb is dimmed down, light from the 2700K bank is gradually turned down, leaving the 2200K bank to take over. Strictly speaking, this shift in color temperature is not equivalent to that of an incandescent bulb when dimmed. But at least it is significantly closer than other dimmable bulbs in the market. [Power Consumption] Previously I have encountered several LED bulbs (such as the LE '75W-equivalent' LED Light Bulbs) with poor power regulation. When the bulb warms up, its power consumption drops and so does its light output. That's why I monitored the power consumption of this Warm Glow bulb over time, to make sure it does not suffer from the same problem. - Initially, the measured power consumption is 11.8W according to my EUM-A1 Power Usage Meter. This is a surprise because the bulb packaging says '9.5W"! - After 15 min, power drops to 10.4W - After another 15 min, power toggles between 9.2W and 9.7W occasionally - Eventually it stabilized at 9.4W. So the rated 9.5W power is accurate after the bulb has warmed up. The power factor is consistently high at PF=0.93, which is a sign of good electrical design. [Dimming Performance] Refer to the picture I uploaded, and you will see that the Warm Glow bulb does become more yellowish when dimmed. Its dimming range, however, is rather limited compared to incandescent bulb. Other LED bulbs maintain essentially the same color temperate whether at full or minimum power. In terms of relative dimming range: - Philips 10.5W 'Slim Style' : down to ~20% - Philips 9.5W 'Warm Glow' (this product): down to ~10% - Philips 11W A19 'Funnel': down to ~5% - Incandescent bulb: less than 1% In terms of audible noise when dimmed: Slim Style gives out loudest buzzing noise that is clearly audible in a quiet room. The Warm Glow is slightly better. The Funnel is the lowest among all LED bulbs I tested. [Bottom Line] The Philips Warm Glow works as advertised, but it is priced relatively high as of this time. So is it worth buying? - If you prefer to see your LED bulb turn more yellowish when dimmed, this Warm Glow bulb is the only choice that I know of. - If you need wider dimming range and don't care about color temperature when dimmed, get the Philips 'Funnel' bulb at about the same cost - If you don't need dimming, consider the Philips Slim Style or Philips 8.5W A19 at about half the cost.