h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

We're about to ban incandescent light bulbs here in NZ and amongst the ensuing discussion is the issue of how the new compact fluorescent bulbs aren't as good for seeing by eg for reading.

So how do they work out comparisons? eg a 20W CF is = to a 100W, supposedly, but it's not really because to the human eye the 20W CF bulb is not as good at illuminating as the 100W incandescent one.

Is the wattage there the amount the bulb is drawing?

Is it possible to get a CF bulb as good at illuminating as an incandescent, or would it not matter how many watts were used?

*

Which leads me to another question. When I was looking at the nearly full moon last night, were there photons hitting my retina that had travelled from the sun to the moon to my eye?

If a 20W fluorescent is the equivalent of a 100W incandescent, then it means it _is_ as good at illuminating. It gives off the same amount of light.

Yes, the wattage is the amount of electrical power it takes in to produce the light and heat. An incandescent produces a lot of heat and a small amount of light. A fluorescent produces much less heat so it doesn't take in as much electrical power.

Yes, the photons have travelled from the sun, bounced off the moon and reached your eye. The moon is actually a very dark grey in colour, almost as dark as a lump of coal. It just looks white because it is much brighter than the background which really is black.

The spectrum of light emitted is different to an incandescent bulb though, giving a different 'quality' of light.

My grandparents found an 18W (I think) bulb inadequate for lighting their dining room, so went for 30W (150W in old money).

Personally, I find the 'new compact fluorescent' jobbies are not satisfactory. They (the ones I've seen so far anyway) take too long to reach a decent level and don't do anywhere near the same (perceived) job when they have done.

So far as I can make out, LEDs will be far better, when they're further developed, though installation may be more costly (transformers etc?).
Can anyone make a proper comparison?

The CFCs do take a long time to warm up. They don't seem to reach full brightness until about 5 minutes after you turn them on. But they use so little power you can leave them on all the time.

"But they use so little power you can leave them on all the time."


No, no, no...

If you turn them off they use no power at all - a better idea IMHO. And if you can put up with the warm-up of 2 to 5 minutes (not long really) we will all use less power.

You can find CF bulbs that give different qualities of light if you don't like the most common ones which I find are either greener or pinker than incandescent.

t.

"But they use so little power you can leave them on all the time." Which would, of course, remove the advantage of having them in the first place.

Yes, but consider a light in a toilet. The toilet will be used in the evening from sunset until people go to bed, which might be 3 hours. If you turn on the light when you go in and turn it off when you leave, it will only just be warming up when it is turned off again. But if you turn it on at sunset and turn it off at bed time, it might only be on for 3 hours, using about 30 watt hours of energy and will give good light in that time.

Just how bright do you need it to be in a toilet?

LED bulbs and mini CFs intended to replace halogen downlighters are still rubbish and don't put out anywhere near enough light. We have halogen ones in the kitchen where you do really want your task lighting to illuminate properly and replaced them all with a variety of led and mini CFs which supposedly give the same level of light but they don't but quite a long way. Gloomy, it was, until be switched half back again.

I'm intrigued by these compact fluorescents that take five minutes to reach full brightness. I've used three or four brands of CFs over the past few years and never experienced this. I have one in the table lamp next to my sofa and four more in the light well (can't think of another description for it) in my kitchen ceiling. The one in the lamp serves me perfectly well for reading books and using the PC keyboard, and as far as I can make out reaches 100% brightness immediately, although it takes a moment or two to actually turn on, in the same way that a fluorescent tube does but without the flickering and much more quickly.

I can't see the justification for keeping one of these permanently lit in, for instance, a bathroom, just because they use less power than an incandescent bulb, but on the other hand, turning a bulb on and off frequently shortens its life. I believe that's even more so with fluorescents, leastways, it was with fluorescent tubes, which is why my dad (an electrician) insisted that we left the fluorescent light in the kitchen on even when we were all in the living room. Perhaps these new compact fluorescents aren't affected in quite the same way, or to a lesser degree. either way, I wouldn't leave one on for the sake of it.

And I have to question some of your maths, Gnomon. 'From sunset until people go to bed' could be eight hours or more during the depths of wintertime in UK latitudes, two to three months in higher latitudes, and my bathroom has no windows at all!

I wouldn't care to have my home lit by LEDs unless they make some which put out a warmer light, more akin to that produced by incandescent bulbs. The first CFs I used were unpleasant in that respect - the light they produced was very similar to a regular fluorescent tube. The light from the CFs I have now is virtually indistinguishable from incandescent light. I recently bought some LED string lights for my balcony and they were very unpleasant indeed. I took them down and replaced them with some old-fashioned incandescent lights. The light from the LEDs was exceedingly harsh and cold.

How much have you spent on your CFs Gosho?

We have a couple that do this (take a few minutes to get to full brightness). They were the ones at the more inexpensive end of the spectrum.

I think you get what you pay for with these types of lights.

The CFCs I tried were a few years ago. The oldest of them actually took about 15 minutes to get to full brightness, but the newer ones were workable within a minute or so, although they did as I said take 5 minutes before they were fully warmed up.

I bought one recently to see have they improved. It was better, but still not good enough to put somewhere where I only want the light on for less than a minute (such as the walkway out to my outside shed).

For safety, I've always kept a 15W incandescent bulb lighting overnight on the landing. I'd be happy if I could replace this with a 1 or 2 W CFC but I haven't seen such a beast.

The little ones we got to replace the down lighters were really expensive and actually, once they have warmed up, they put out a decent amount of light.

The LEDs though, they were either way too yellow or way too blue so I either looked like I had liver problems or looked like I had been stored in a freezer. And they were fairly dim.

I can't remember. I bought them from different shops, and months or maybe years apart, so a price comparison is difficult. Each of the shops I bought them from didn't have much of a range of choice so I had to buy what they had. My only real choice was the wattage. I know that the ones I'm using right now, and which I like a lot, are General Electric, but I used them all so I don't have any packaging left to get model numbers from. Compared to the incandescent bulbs that were on the selves next to them they didn't seem outrageously expensive, especially considering the energy savings and the longer lifespan.

When CF bulbs first came out 10 or so years ago they did have a very noticeable warm up time of minutes (as well as that horrible flicker, and creepy coloured glow). That has been improved hugely. I personally don't notice any warm up time now but then I'm not using a single CF bulb in a small room like a toilet where it might be noticeable.

The not as bright issue is very annoying for people like me who like bright light. I usually use 100W incandescents in the living room and kitchen, even in lamps where other people would use a 60W bulb.

I surmise from this thread that the comparison in my OP (20W = 100W) is not about how humans exeperience light, but about how much light is being output? How would that be measured?

Orcus, can you say more about the differences in light spectrum? I'm guessing that people also perceive this differently, hence the lack of brightness in CFs bothers some people and not others.

Traveller in Time working in LED lights
"The LED lights get better every year, the will be supplied with in-connector internal supply soon you will no longer need a seperate supply, The light output seems to be limited by the emitter surface (a tiny semiconductor chip deep inside < A762662 > 'Light-emitting Diodes')

There is one thing obviously missing in Fluorescent lights: they are no heat source. Even though we can not see the infra red rays, we certainly experience them. You will notice on a warm night outside the Compact Fluorescent lights feel nearly as good as Incandescent lights.

I am eagerly waiting for HID lights as used in cars to become reasonable priced , high light output with 'tiny' focus. "

Hi kea

Long time, no chat.

Take a look here - http://www.bltdirect.com/lampColourTemperatures.php . Most energy saving bulbs burn at 2700 Kelvin.

t. or maybe

I saw an LED torch in use when I was camping this weekend and was impressed, although it would be a weird colour for indoor lighting.

Well turvy has beaten me to it there

I must say that I find the 'colour temperature' thing a tad misleading though. That is presumably the 'colour' a black body radiator would have to be at that temperature (similar to 'red hot' and 'white hot') but as mentioned earlier also, these things do not emit at all wavelengths like a black body. So in fact they're not very hot at all.