Wikipedia:Reference desk/Archives/Science/2020 October 23

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October 23

Portuguese man o war reproduction.

Apparently men o war are colonies of different organisms rather than individuals?

Yet only one type of organism that composes the man o war reproduces?

How does the entire thing (all parts) increase its number then?

146.200.128.134 (talk) 05:18, 23 October 2020 (UTC)

Although a Portuguese man o' war is considered a unified colony of sets of different specialized members, it's still a single organism and apparently all the members have the same DNA(!). They reproduce sexually (distinct male vs female meno' war), and then the cell cluster buds off as the component types begin to differentiate. Google for "Portuguese man o' war" reproduction. DMacks (talk) 05:47, 23 October 2020 (UTC)

See Siphonophorae#Reproduction.-gadfium 05:50, 23 October 2020 (UTC)

Turning On LED Lightbulb

My question is whether I save electrical energy by turning a 3-way LED light bulb off when I am not using it, and then turning it back on when I am using it, or whether more electric energy is wasted in bringing the bulb up to emitting full-strength light. In other words, what amount of on-time is the initial power surge comparable to?

I understand that with conventional fluorescent bulbs, a relatively large surge of power is used to bring the lamp up to fluorescing, and then relatively light energy is used to continue the generation of light. Is that correct? I have also heard it both ways about traditional incandescent bulbs, both that a large amount of energy is required to get the filament white-hot, and that relatively little energy is used to bring them on. Are there reliable sources?

What rule should I follow with 3-way LED bulbs, which are neither incandescent nor fluorescent? Robert McClenon (talk) 18:08, 23 October 2020 (UTC)

There is no energy benefit in leaving fluorescent lights on--Phil Holmes (talk) 09:14, 24 October 2020 (UTC)

The topic is inrush current. LED bulbs (considering together "LED + driver-circuitry") do have a spike at the start. But it appears from googling that the spike is a smaller total amount ([current] times [time]) than other bulb-types. See for example [1]. If there's less totall startup-cost, then even shorter turned-off spans are still an advantage in terms of energy economy. DMacks (talk) 19:35, 23 October 2020 (UTC)

If you're talking about saving energy by leaving the light on, forget it, whether you have fluorescents or any other type of lights in common use. As the article says, whatever inrush current there is has to get past whatever sort of fuse or circuit breaker is installed, and that means there can't be much of it. What you might need to think about is whether turning the light repeatedly on and off will shorten its life. I have no reliable information about that. --174.89.48.182 (talk) 23:21, 23 October 2020 (UTC)

Great answer. Here's the results of an experiment I have just done. (Why would I buy a USB ammeter? to answer questions like this), on an LED light that plugs into a USB socket. It appears to be massively overdamped, there is no real sign of an inrush current, on the scale of 0.3 seconds, so I ssupect if you are switching on and off on the order of minutes then you are better off switching it off. BUT, you are also wearing the swicth and PS and LED out by switching them. Greglocock (talk) 00:09, 24 October 2020 (UTC)

What you're thinking about with fluorescent lamps are the "instant-on" or "cold-start" lamps. These have a heater circuit that briefly applies current across the electrodes when the lamp is switched on. Lamps that don't have this tend to be dim when first switched on and take a few minutes to get to full brightness, when the electrodes reach operating temperature. LEDs don't have anything like this. The only inrush current is whatever the power supply pulls when switched on. --47.146.63.87 (talk) 17:30, 24 October 2020 (UTC)

Thank you. I will add that I think that there was a reason to leave incandescent bulbs on rather than turning them on and off, especially in earlier decades (e.g., the 1950s through 1970s), and that was that switching them on and off shortened the life of the bulb, and the bulbs only lasted a few months anyway. Incandescent bulbs last longer than they did in the past, and other types of bulbs last longer than incandescent bulbs. Robert McClenon (talk) 00:39, 25 October 2020 (UTC)