An attractive feature of filament lamps is that they become warmer as you dim them. As the filament dims and becomes less intense, the colour changes to a warmer more orange and yellow appearance. The colour temperature, and CCT reduces as they dim. Until recently, this effect was missing from their LED equivalents.
Whilst LED lamps could copy the physical shape and dim to low levels (some better than others), they always retained the same colour appearance. They did not become warmer as the light output reduced. Now, however, you can buy LED retrofit lamps that become warmer in appearance as you dim them.
We have chosen lamps from the three biggest suppliers and compared them with a filament lamp. We put each LED lamp on the same circuit as the filament lamp so we could see a side by side comparison.
It is worth mentioning that dimming filament lamps never actually saves much energy since the light emitted reduces much faster than the power consumed. Typically, a 10 percent reduction in the voltage gives a 35 percent reduction in light output. The LED equivalents are much more linear in this respect.
The filament lamp we used was a 70W Eco type with a CCT of approximately 2,800K at full output. Since it was on the same circuit as the LED lamps, the lowest we could dim it (before the LED lamps extinguished) was about 1,650K.
It had an opal or frosted bulb and at low dimming levels you could see the filament glowing inside.
We have chosen 'A-line' type lamps, which most people would call a round bulb, since it is these applications where the dim to warm effect is most appreciated. We have also included two 'LED filament' types.
The photos, left to right, show the lamp in its off, dimmed and maximum output positions.
Standard incandescent filament 'Eco lamp'
This is one of the newer Eco-type incandescent lamps which uses a halogen capsule to improve the efficacy from about 12 lm/W of a standard incandescent filament lamp to about 17 lm/W. Of course, it can dim smoothly to zero output, albeit the colour is quite yellow. The big disadvantage, apart from its terrible efficacy, is that the light output drops much quicker than the power reduction so you don’t save that much energy.
Ledvance Classic A60 Glow Dim
Ledvance is the new name for the Osram general lighting lamps business.
This has four filaments in a clear bulb. When switched off, two are yellow in appearance and two are orange. These have slightly different CCTs and the balance between the two alters as you dim up and down.
Ledvance Classic A55 Glow Dim
The Classic A60 has an opal bulb which is completely uniform in appearance at all dimming levels and all viewing directions. It dimmed smoothly and always looked good.
Megaman Classic Dim to Warm
This has an opal bulb and dimmed smoothly. However, the opal finish is thin and you can easily see the two inner rings of pinhead-size LEDs inside. These are visible at all levels of brightness. It’s not unattractive, but it is noticeable. It was also the least efficient of the LED lamps we tested.
Philips Dimmable LED Warm Glow
This is different in appearance from the others in that it has a clear bulb which is slightly flattened at the top. Inside, there is a clear plastic moulding which adds sparkle when switched on. It doesn’t pretend to be a filament lamp and, in my opinion, is more attractive for being a modern design.
Philips Classic Dim Tone
This version has a clear bulb and five LED filaments which are orange in appearance when switched off. These progressively switch on and become brighter and brighter as you increase the power.
Data is as quoted by the manufacturers: