LED bulbs

High colour temperature indoors is useless for it. Daylight at 10,000 - 100,000 lux (e.g. outdoors) would be fine, and even down to 3,000 lux would be workable.

Reply to
Andrew Gabriel
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Remember that color temperature isn't the whole story either.

That applies only really to objects that emit light because they are hot

- where you get a broad spectral emissions.

LEDS and fluorescent devices emit in specific bands which are matched to give approximately similar results but not exact ones. Which is why some colours look weird under that sort of lighting

Reply to
The Natural Philosopher

All you're doing is confuse me. ;-)

BTW, I wasn't talking about so called daylight domestic tubes, etc.

Reply to
Dave Plowman (News)

This is the whole point. The 'eye' will adjust to different colour temperatures to a great extent. What it can't do is add in parts of the spectrum which are missing or very uneven. As with all low cost CFLs and LEDs. Which is why many find them unnatural and unpleasant - nothing really to do with colour temperature.

Reply to
Dave Plowman (News)

And if you want to see that in action, buy a diffraction grating from ebay (looks like a 35mm slide, because it is).

For folk who didn't do physics, if you look through one, it is similar to using a prism to split light up into the colours of the rainbow - only it works way better.

It becomes clear very quickly how good a light is. A tungsten lamp will give you a streak that does indeed have all the colours if the rainbow.

A CFL might only give you 5-7 ribbons of colour with gaps between depending.

The minimum that would pass for white would be 3 bands (RGB) but as pointed out, this would be terrible for illumination, though fine for backwash colour lighting.

Reply to
Tim Watts

Here: 4 colours,

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3 here on this CFL

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And halogen:

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Reply to
Tim Watts

The other interesting one is to make up a light box with the primary colours with each adjustable so you can produce near any colour. A monitor where you can adjust the RGB gains individually might do quite well.

Now get a narrow spectrum light like low pressure sodium. Match the colour of the light box to it as best you can.

Now ask someone else to do the same.

You'll not agree - and by a vast margin.

This is said to show we all actually see colours differently within our brain - but of course learn what their names are. Or something.

Reply to
Dave Plowman (News)

You should have passed the light through a narrow slit before the diffraction grating to properly demonstrate the differences.

Reply to
Johny B Good

I didn't - these are just random google images :)

Reply to
Tim Watts

The CRI 80-89 tubes are tri-phosphor - 3 phosphors (RGB). There are also some visible lines from the mercury discharge, most notably the royal blue (as distinct from the lighter blue phosphor band), but also ome dimmer ones more towards the middle of the visible spectrum.

If you have a small tube running on 50Hz, you can also nicely see the different phosphor persistance by swinging it around your head on the power lead (nothing can go wrong here;-) Won't work with a CFL on high frequency control gear (even if you spin it 1000 times faster), because the discharge does not extinguish between each current reversal.

That's standard fluorescent lighting. CRI 90+ tubes use more than 3 phosphor colours, but they aren't easily available, and are more expensive and less efficient.

Reply to
Andrew Gabriel

You have the same 4 in both, but the two blues are hard to distinguish in the second case. The outside blue is one of the mercury lines, not a phosphor.

Somewhere, I have a set of glasses with vertical diffraction gratings for this purpose. Was a free giveaway at a trade lighting show.

Reply to
Andrew Gabriel

I guess it must have been 4 then (including the mercury) - the blue part was quite smeared so it was hard to tell.

I did not have a high CRI lamp to test so the rest was supposition.

If you stand under a grid line holding a 6' tube vertically at night it glows. I have not tried :)

Reply to
Tim Watts

Any shovelware CD with an aluminium reflective layer will do. The cornflake packet version is an optional extra.

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Holding a CD at glancing incidence and looking down onto it you can get a high resolution spectrum of the sun that is sufficiently good to see Fraunhofer absorbtion lines. How to do it online at:

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Reply to
Martin Brown

Or look at the reflection in a CD.

-- Richard

Reply to
Richard Tobin

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Possible, but how many will do so? I have such a meter, and now have a needlessly bright LED bulb in the vestibule, but haven't got round to checking its consumption. Don't know how well the meter would work with a switch mode power supply which I imagine must be built into the LED, but it does correctly show 30 watts on something else.

Reply to
Windmill

Those two digital wattmeters that I recommended (unlike that damned Aldi DEM1739 "digital wattmeter") will show true power on such loads (as, inevitably, will my Metrawatt analogue meter - it's only _really_ nasty very high and narrow current pulses from the thyristor based PSUs used in some older domestic CRT based TV sets that can cause some under-reading due to core saturation effects in the field winding circuit which effect can be confirmed by selecting a higher amp range (1 to 5 or 5 to 25 amp settings) which scrunches up the (more accurate) readings to the low end of the scale).

Reply to
Johny B Good

Have you seen the failure rates?

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About half the reviews are showing them dying in short order.

This is why I usually ignore "no name" LEDs - except maybe LEDHut who put their own guarantee on them.

Reply to
Tim Watts

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