I saw one at the Brighton Earthship and was not impressed. Not the latest model, admittedly. From inside it looked like an underpowered electric lamp. The light was dim and bluish - probably because there was no direct sunlight (normal for UK, I'm afraid).

Soon I expect it will be more economical, and better for the building's insulation, to install an off-grid PV panel on the roof, wired to energy-efficient lamps in the part of the building that lacks natural light.

My house design has a short corridor on the north side from the front door past the guest bedroom and bathroom doors opening out into the kitchen and living room. It's likely to be a bit dark so I did some calculations as to whether or not to put a small roof window in.

Assuming 2 hours lighting an evening and taking into account the need to source the energy for the extra heat-loss through the window (small triple glazed Velux) vs an approx 0.1 W/m²·K roof the capital cost of PV and batteries needed for lighting came out to £30 less, IIRC. The cost of the actual lights are not included as one would assume they're needed anyway.

For this application 2 hours an evening is probably an over-estimate. When it's sunny the PV energy can be used for other things but extra light through a north facing window isn't much use except when that corridor is in use.

I do regret not having a window to the north at all (other than in the light in the front door from the porch/greenhouse out) but maybe I'll spend that £30 on a webcam

Wookey has previously joked (I think it was a joke) about building a house with no windows at all - PV + LED lighting and web cams.

BTW, PV direct to LEDs (no batteries or anything) would work very proportionally as both are current devices. Just pick your LEDs so that each string has a total Vf just a bit less than the Vmpp of the panel. If you have multiple strings of LEDs then each would want a small resistor to keep the currents balanced.

Posted By: Gotanewlifethe light is not changed in any way and can only be blueish if the dome has been tinted.

Good to hear a success story - albeit from a place where there is more sunlight and less concern about heat loss.
I don't know whether the light tube I saw was tinted. But since direct sunlight appears slightly yellow, and light from a clear or cloudy sky appears blue, I would have thought it was entirely possible for an untinted tube to emit a bluish light into the building. The subjective colours are affected by context: sky-light will appear more strongly blue if seen next to a 'warmer' light-source such as halogen lamps or the sun itself.

Right, I'm going to up this again!

I've an office on the N side of the house. Two narrow, shaded windows to the NW mean very little light, and I have to have the LEDs on whenever it's not bright outside. I also would greatly prefer daylight to LED light.

This is a lean-to, so a roof window is a possibility. However fitting that into the aesthetic is a bit difficult for a couple of reasons, and I think a sun pipe would look better from outside. With a short tube length I think this is ideal.

So now the sun pipe people appear to be getting their act together with numbers.

http://www.solatube.co.uk/products/ claim U down to 0.5W/m2K .

What about air tightness, anyone know?

Posted By: djhI'm also not encouraged by their mention of specific supposed aspects of Passive House, without being a certified component. Smoke and mirrors.

Yes, I thought that.

Will try to ring them.

Posted By: tonyplastic dome not durable enough

I designed and manufactured some at the end of the last century. They are still in good condition.

I called them yesterday, mentioned the above questions. No call back yet...