LED Reading Lamps

[arjaybe]

I would like to know what specs people prefer in LED light bulbs. Kelvins. Lumens. Anything else. I've found that cooler bulbs (2700K) give a nicer light, but whiter ones (5000K and up) are brighter.

[dwig]

The warmer lamps (<3500k) are my preference, especially when reading in the evenings.

[arjaybe]

Okay. "Warmer" light, cooler temperature.-) I'll have to try a bulb at 3500K and see if it's bright enough. 2700K is nice for ambient light, and I CAN read by it, but I could use something a little brighter.

[dwig]

Originally Posted by arjaybe

Okay. "Warmer" light, cooler temperature.-) ...

The long established convention is to use the terms "warmer" and "cooler" to refer to the visual impression and not the temperature of a theoretical "black body radiator" that yields the same balance of emissions across the visual spectrum. The yellower/redder light produced by the lower temperature radiator is perceived as "warmer" and the bluer balance produced at higher temperatures is perceived as "cooler". Misusing the terms can lead to confusion in your search.

If the warmer options are dimmer per watt then simply look for higher wattage lamps.

[arjaybe]

Yeah, I just thought it was funny. I think the "warm" and "cool" might have come from fluorescents. "Cool white" and all that. I'll definitely be experimenting with kelvins and lumens.

[Rumpelteazer]

Regarding kelvins and colour temperature:

2200-2500k very warm white, colour of decorative light bulbs
2700k is considered warm white, the colour of incandescent lightbulbs
3000k, also a warm white, but slightly cooler, the colour of halogen
4000k, cool white
6500k, very cool white, often referred to as daylight

In fluorescent tube they had a coding (at least in the Netherlands) that did not only give the kelvins but also the quality of light: 827 is 2700k in quality 8, 840 is a good quality cool white, but 640 is a lower quality 4000k, with a bluish tint to it. You also have the daylight tubes, which are quality 9; 950, 960, etc, but because of the quality of light they give 30% less light than the quality 8 tubes.

In LEDs I've yet to come across one (we sell light sources in our store) that give the quality on the box, only the kelvins. Especially in the beginning the kelvins didn't mean much. It might be a bulb that was 2700k but it could have a blue, green, orange or purple hue to it. They've worked that out, luckily. But we still have bulbs that are all 2200k but different brands are different colours; one might be more orangy, another brand more yellowish.

[dwig]

Originally Posted by Rumpelteazer

...
In fluorescent tube they had a coding (at least in the Netherlands) that did not only give the kelvins but also the quality of light: 827 is 2700k in quality 8, 840 is a good quality cool white, but 640 is a lower quality 4000k, with a bluish tint to it. You also have the daylight tubes, which are quality 9; 950, 960, etc, but because of the quality of light they give 30% less light than the quality 8 tubes.
...

The "standard" for the quality value is the Color Rendering Index (CRI), which in North America is normally listed as a 2-digit number. the CRI represents the percentage accuracy of the light source compared to a Black Body Radiator of the same Kelvin temp. The Euro style quality numbering seems to parallel CRI rounded to a single digit (e.g. Quality 8 ~= CRI 80).

For normal use, a CRI of 80 or greater is fine. For color matching or color photography, a CRI of 90 is considered a minimum.

[arjaybe]

So, I have to look at CRI, too. They don't seem to put that on the box, though.

[BetterRed]

Thank goodness, and contrary to overseas news reports, in NSW at least, we can still buy incandescent bulbs. I'm fine with LEDs in general lighting, but I don't like them in reading lamps - they deliver a beam of light rather than a pool.

BR

[arjaybe]

Oh no! I looked into CRI and now I'm going to obsess about it. Can I be satisfied with 80, or will I have to insist on 90?

[Rumpelteazer]

We were once told by a representative of a supplier that CRI was how energy efficient a LED bulb was. I didn't believe it after checking the packaging of some bulbs, but I never looked into it any further. I checked this morning, and only one brand lists the CRI, and it's very high at 95.

One thing you should know about lumen: they've changed, at least in Europe, how they measure it a couple of years back. Before manufacturers could measure it any way they wanted to. So they measured it at the point where the bulb gives off most light. Iirc they now have to do multiple measures and average it. So a new LED light bulb of 600 lumen gives more light than the old incandescent bulbs of 60 watt, which were usually between 650 and 700 lumen.

Also, in Europe when the started phasing out the incandescent light bulb there were, and still are, some loopholes. Special bulbs were exempt. So they started selling those for regular incandescents. First they sold the reinforced ones, which gave about 10% less light than a regular bulb. That loophole was closed two years ago, now they sell 300 degree Celcius lightbulbs, mostly used in ovens, as normal ones and those give off even less light than the reinforced ones (LED doesn't like heat, so there's no alternative for these bulbs yet). Also, if they put on the box that the bulb is meant for outdoor lighting they are allowed, that's a trick the manufacturers of decorative bulbs use, which use 40 watt, but only give off 160 lumen (about 20 watt regular lightbulb).

[Rumpelteazer]

Originally Posted by BetterRed

Thank goodness, and contrary to overseas news reports, in NSW at least, we can still buy incandescent bulbs. I'm fine with LEDs in general lighting, but I don't like them in reading lamps - they deliver a beam of light rather than a pool.

BR

You might want to look into "filament LEDs", like these, they use rods with tiny LEDs in them and depending on how the rods are placed the light they give is nearly identical to an incandescent bulb and they don't have the spotlight effect.

Keep in mind LEDs don't like warmth, so if the light fixture is often on for longer periods of time make sure the warmth can escape, especially above the bulb, heat rises. Otherwise you keep replacing bulbs.

[BetterRed]

Originally Posted by Rumpelteazer

You might want to look into "filament LEDs",

Thanks, I'll try to find a local retailer where I can buy one and give it a try.

BR

[arjaybe]

Today I bought a bulb rated at 2700K and 1550 lumens. It seems to be okay from the short test I've given it so far. We'll have to see how it holds up to several hours of reading. It has the warm light I like with the brightness I need.

No mention on the box of CRI, though. I get the feeling that CRI is only mentioned with specialty bulbs, or bulbs for special uses. So far, anyway.

[Bruno_Little]

I use for reading LED tapes hidden behind a plastic panel on a metal profile