[lean bean]

Does a tv use less energy when used for listening to radio than when used to watch a programme?

[David Cooper]

I suppose a very dark film might use less energy than a radio station which fills the screen with a bright banner, but then it might use more energy processing the signal for the moving images, so that's a hard one to work out without a lot of knowledge of power usages of screen and processor. There's also the screen type to consider - CRTs and OLEDs will only use energy to light up pixels, whereas an LED backlit display is lighting the whole screen equally all the time, which leads to the other issue of how much energy it takes to switch the pixel RGB LCD filters on and off and whether energy is required to keep them in one of those states.

[CliffordK]

If you control for sound, age of the device, etc, then your TV does more signal processing, and has a larger display, so it should use more juice.

It has been noted elsewhere that it is possible to build a "crystal radio" that is powered 100% by the captured radio waves. 

I don't believe it is possible to do the same with a TV, at least not without a HUGE antenna.

However, as David mentioned, you can also get compact versions of both radios and TVs that use very little power.

[lean bean]

Thanks chaps.
I think whatever that is in the lower picture would make a good alarm clock, especially for me.

[syhprum]

The remote control on my LED TV has a button that permits you to switch of the light source when using it as a radio saving a large proportion of the power.

[graham.d]

I would expect the TV to always use more power because, in general, there wouldn't be sufficient incentive to engineer the design to save the power and to do so would increase the cost of design and, probably, also the component cost. However the difference may not be very much if, as alluded to above, the screen backlight and some of the video processing can be turned off. I assume this would be comparing radio received via the digital, over air, channels through a TV aerial with DAB radio. If comparing with FM radio then the radio wins hands down as the digital processing in DAB radio is significant (and not dissimilar from that needed in a TV) and consumes a fair bit of power.