Question About Incandescent Light Spectrum when Dimmed

  • Does anyone have information about the light spectrum from incandescent lights when they are dimmed to low levels?

    I would like to determine how much, if any, blue light they emit when dimmed. If there is little or no blue light, then I'm thinking they might be a good alternative for lighting in the evening hours, as opposed to installing color changing, dimmable LEDs for example.

    Any comments would be appreciated.

  • I think I can answer my own question. I found the following web page:

    Point 3, about midway down the page, has a good explanation:

    "As the temperature of an object increases, more light is produced at all wavelengths than when it was cooler. You can see this effect with a light bulb wired to a dimmer switch. As you raise the current going to the bulb, the bulb's filament gets hotter and brighter."

    So if I understand correctly incandescent and halogen bulbs produce light by heating up a tungsten filament. And there is a physical relationship between the temperature of something and the light spectrum that it emits. When something has a cooler temperature the light spectrum shifts to lower energy wavelengths - in other words towards the red side of the spectrum.

    This basically means that when an incandescent or halogen bulb is dimmed more red and yellow light will be emitted and less blue as a proportion of the total light spectrum. So there is kind of a double effect at reducing the total blue light through dimming - the overall amount of light emitted across the entire spectrum is reduced, and the spectrum shifts away from blue light to red light.

    If I had remembered my high school physics I wouldn't have needed to search for this on the internet!

  • A typical wall dimmer at "half" will lower the color temperature to 1900-2000K. So it is very warm when you dim it - and this is pretty important.

    There are some LEDs that can emulate this too (e.g., Philips Warm Glow).

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