There's something off about LED bulbs • Hacker News Board

Re: There's something off about LED bulbs

#961

Post by cogman10 » Tue, Apr 04, 2023, 3:38 AM UTC

tremon wrote: post #919

xpe wrote: post #864

Earlier quoted context omitted.

Until I see someone defining a representative example and running the numbers, I'm skeptical of their DC vs AC commentary. I say this, because I was guilty of this exact shortcut thinking (in another comment). But I paused and thought to myself "I should run the numbers before just repeating the usual voltage drop criticism". So I compared scenarios and it depends a lot on the topology, lengths, costs, and situation…

I'm skeptical of their DC vs AC commentary It's not about DC vs AC, it's high-voltage vs low-voltage. The power dissipation by wire resistance scales with the square of the current ($P=RI^2$), and low line voltage means that you need large currents to transmit the same amount of power.

Whether or not that's feasible is going to depend a lot on the application. I don't think we'd ever fully rid homes of AC sockets, it's too useful for things like vacuum cleaners or space heaters.

But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. Every light in a home, phone chargers, tablet chargers, computer monitors, televisions, computers? (maybe not gaming rigs, but certainly laptops and nucs).

Re: There's something off about LED bulbs

#962

Post by drcongo » Tue, Apr 04, 2023, 10:49 AM UTC

gniv wrote: post #196

drcongo wrote: post #37

I don't recognise any of the issues mentioned in this article at all and there must be a hundred odd LED bulbs in my house. I'm wondering if this is a US-specific thing, I'm in the UK.

> I'm wondering if this is a US-specific thing, I'm in the UK. I think so. I am in France now and all I can easily buy are expensive and good quality bulbs. In US the quality was all over the place and price was not always a good proxy.

Thanks for the added datapoint.

Re: There's something off about LED bulbs

#963

Post by GordonS » Tue, Apr 04, 2023, 5:42 PM UTC

wheels wrote: post #780

fsckboy wrote: post #652

Earlier quoted context omitted.

I do have different memories than you about buying lightbulbs. I remember thinking 60-watt bulbs are frustratingly dim, 75 watt bulbs are a minimum, but what I really wanted every time was a 100 watt bulb, it just improves visual acuity tremendously. And my frustration with LED and flourescents, etc is that I can't find the equivalent of my good old 100 watt bulb; whatever the new rating systems are, it's all an excu…

It's really not that hard to find 15w LEDs with CRI95+. 15w will be approximately equivalent to a 100 watt bulb. A quick Amazon search pulls up multiple options. Recently I even got out the big guns and bought this thing, mainly to replace my halogen floor lamp. It's 40w, and more like the equivalent to a 250w incandescent, though it is awkwardly ginormous. https://www.aliexpress.com/item/4000240793250.html

15W should approximate a 100W incandescent bulb - but IME it's hard to find 15W LEDs that do; I've tried several (at a variety of price points), and none were as bright as the 100W.

Re: There's something off about LED bulbs

#964

Post by GordonS » Tue, Apr 04, 2023, 5:55 PM UTC

pixiemaster wrote: post #665

fsckboy wrote: post #652

Earlier quoted context omitted.

I do have different memories than you about buying lightbulbs. I remember thinking 60-watt bulbs are frustratingly dim, 75 watt bulbs are a minimum, but what I really wanted every time was a 100 watt bulb, it just improves visual acuity tremendously. And my frustration with LED and flourescents, etc is that I can't find the equivalent of my good old 100 watt bulb; whatever the new rating systems are, it's all an excu…

i had a similar view, until i found COB LED stripes (with dimmers), with 20W per m (LED W, not equivalent, i have mounted a few of those 3-10m (!), and now can have dimmed 1% background lights and hospital style brightness as well.

How are they aesthetically? Like, are they glued raw to the wall, or have you used some kind of covering?

Re: There's something off about LED bulbs

#965

Post by sidewndr46 » Wed, Apr 05, 2023, 8:03 PM UTC

consp wrote: post #895

sidewndr46 wrote: post #120

Earlier quoted context omitted.

It is interesting you cite that the cost has went up for lighting. Where I live the government owned utility often raises their rates per kwHr. One of the reasons they cite is the increase in efficiency leading to a drop in revenue each year. The same utility pays for those efficiency projects.

My network and kWh cost are split and the network cost have risen far less than kWh cost. Also the network cost are constant. Looking at where those are used for the main cost are in peak usage capacity which efficiency actually lowers.

This would make much more sense, but if they billed by network cost I think people would quickly figure out there is no real reason to conserve electricity here. The cost of generation is so low (in fact negative sometimes) that it doesn't make a bit of difference.

Re: There's something off about LED bulbs

#966

Post by midoridensha » Thu, Apr 06, 2023, 2:25 AM UTC

cogman10 wrote: post #961

tremon wrote: post #919

Earlier quoted context omitted.

I'm skeptical of their DC vs AC commentary It's not about DC vs AC, it's high-voltage vs low-voltage. The power dissipation by wire resistance scales with the square of the current ($P=RI^2$), and low line voltage means that you need large currents to transmit the same amount of power.

Whether or not that's feasible is going to depend a lot on the application. I don't think we'd ever fully rid homes of AC sockets, it's too useful for things like vacuum cleaners or space heaters. But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine. Every light in a home, phone chargers, tablet chargers, computer monitors, televisions, computers? (mayb…

>But what about the sub 100W or even 200W applications? That's where I think something like 48VDC would start to shine.

How so? Exactly what benefit does it have over the current AC mains? With 48VDC, you'd still need to use DC-to-DC converters to power everything. I fail to see how that's any kind of improvement over the current switch-mode power supplies used. Instead, it'll just be less efficient because you'll get higher line losses in the power lines in the walls and all the way from wherever that 48VDC is coming from. If that's from a big SMPS in a closet somewhere, that's going to have its own losses. Overall, the entire system will have lower efficiency compared to the current system.

Exactly what problem are you trying to solve with this idea? If you think you're going to eliminate SMPSs in all your electronic equipment, you're not; that's a fantasy. Everything needs a power supply because electronics only work at very low voltages (5V, 3.3V, even 1.8V in places, now 20V with USB3) and most equipment has some kind of peculiar voltage requirements, and usually multiple different requirements inside the same device. There's no improvement in efficiency by running a computer, for instance, from 48VDC vs. 120VAC or 240VAC, in fact it's probably worse.