What Kelvin temperature/color for shop light bulbs?

J

Jason Fry

Knifemaker / Craftsman / Service Provider
Joined
Jun 5, 2008
Messages
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Now that they have fluorescent bulbs in quite a few frequencies, does anyone have data or suggestions on what bulbs work best in a knife shop for showing blade scratches, etc?

I know I had a mix of bulbs in my old shop, and never had to replace any. I discovered that one of the more orange ones wouldn't show scratches much, and things improved when I moved one of the more bluish bulbs in there. Unfortunately, I don't live there any more and didn't take down numbers on the bulb frequency.
 
I just recently finished building a shop and looked into a number of types of shop lights. From the research I did LED's are the way to go. Color rendition recommendations varied between 4000K and 5000K. These are what I ended up with. I got them at Sam's Club but I think you can get them on Amazon for around $35 each. I love the lighting in my shop with these.
IMG_6366 by Robert Erickson, on Flickr

FullSizeRender 66 by Robert Erickson, on Flickr
 
I found that the whiter (higher k) the bulb the better 5000K-6000K. The K number is not frequency, it's kelvin color. Also CRI is very important, the higher the CRI the truer the colors will look in your shop.
 
I did what Robert did, but I've also found the direction of the light makes a difference for seeing scratches, so at my workbench and grinders I have a couple architect lights that can be positioned how I want, and it makes a huge difference in how easy scratches are to see, especially on materials they're usually hard for me to spot like darker woods or G10.
 
I recommend going with a variety. You can see certain scratches in certain colors and/or type of lights. Although yes, having some high CRI bulbs, definitely helps to see color correctly, although, whether that will translate once you take a knife to a show, is a crap shoot, depending on the lighting there.

Tube fluorescents are very directional, and IMO, don't reveal flaws very well. They tend to cast in a direct line laterally from the sides of the tubes. Shadow easily. I've got a bunch of them, all over the shop, but supplement with lots of hanging contractor type "spot" lights with the clamp ends, and put LED floods and spots in them, to give me plenty of light around my grinders, and in the areas I file and hand sand.

You really can't have enough light.

One tip: many places, the local electrical companies are subsidizing LED light bulb prices, if you know where to get them. Here in NC, Duke Energy has supplied the "local" hardware stores, with super cheap LEDs in lots of different types, at typically $2 each, for very good quality, high lumen bulbs. The trick is, you can only find them, at the locally owned, and franchise stores, like Ace, and True Value. Not at the big box stores, where the same bulbs will be 10x as much.

I've been buying half a dozen every time I go to get some part, figure I"ll stock up for the next 10 years, cause I don't really expect them to get much cheaper than these. The only directional floods I can find like these have been $20 each everywhere else.
 
I got a bunch of 5000K 4 ft. LED tubes from greenlightdepot, too. They are nice and bright and white, and were easy install into my old T12 fixtures, just bypassing the ballasts. I recommend them wholeheartedly.
 
Ken H> said:
Javan, that is the best price around on LED bulbs for sure. I ordered 6 LED bulbs from these folks, 4 of the $5 tubes and 2 of the $6 tubes. I've installed 2 of them and so far they're working good. https://greenlightdepot.com/collections/4ft-led-tubes Shipping seems like was around $11?
Click to expand...


Ken, ironically, the subsidized bulbs I was mentioning, are GreenLight brand. They seem to be very good quality. I got spots, floods (large and small), various standard fixture bulbs, and they even have a filament LED now, that looks like an old-school bulb, and has a very nice classic amber/yellow color. I've replaced all the bulbs in my living space with them, which I'm not sure if it's just nostalgia or what, but I find it very relaxing. Before I tried them, I had no idea I was missing it, but something about that clinical neutral/cool white color of floros and most LEDS, makes me tense. It's great for work, but crap for sipping scotch, smoking a cigar, and relaxing after forging all day. I didn't see any on the above link, but here's a link on greenlight's website: http://www.greenliteusa.com/en/lights/1927-led-7w-omni-clear-a19-filament.html I know it's totally a topic digression, but seriously, if you remember pre-CFL lighting, buy some of these things, and at least replace the bulbs in your floor lamps for reading. They're magic.

Another maker friend of mine, here in NC, also got a multi-hundred dollar discount on some very high end LED fixtures, that are bright as the sun, saving over 60% off retail, when his electrician was in the plant installing some circuits. Same deal, electric co, was offering a deal.

Apparently it's all tied up in how they manage to finagle their rate hikes from the state. I'm not saying it's available in every state, but all of us would be smart to call our utility and ask if they have any incentives, discounts, rebates, etc., I'm willing bet, that in most cases, they do, but there are caveats, and you have to actually ask, don't think they'll just throw money our way without us at least taking the initiative. ;)
 
I replaced miserable 8ft flourescents with $35 linkable LEDs from Home Despot. The light is less directional, which is good for everything except seeing fine scratches. I have an architect lamp stuck in a mic stand for close-up finishing work in the vise. It's also an LED, but a warmer color and easier to point.
 
I fixed the title for you.

For spot lighting and other close work light, I use the higher temperature bulbs where color and clarity is important - 6500K.
They are a bit harsh on the eyes, so for general overhead lighting, I drop down to 5000K.
 
Can’t add much to what has already been posted, as I’m using basically the same lighting as others. I will recommend solatubes to get real daylight into your shop at least during daylight hours.

http://www.solatube.com/

I have two industrial ones in my shop and on a bright day, I feel like wearing sunglasses.
 
Swapped out the lights in the garage with 4100K units from Costco. I like them just fine.

Direct replacement, no reconfiguration needed. Switched for the extended life aspect, energy savings are just a bonus.
 
I agree with 5000K for tubes and the LED spots at different angles for lots of light. Strangely though, all this light in the shop does not show the one scratch that immediately pops out under the crappy lighting at the knife show!
 
On the topic of frequency, some LEDs especially cheaper ones can have some flicker. It can be due to output control, or heat management, or just poorly designed transformers. I'd suggest that anyone wanting to get lights for near any moving tooling, grinder, lathe, belt etc, make sure you can either return the lights if they don't work for you, or at least test them out really well before doing the entire install. Not everyone is as sensitive to it, but I can imagine it would cause major eye-strain if you were watching your belt grinder under a strobe light. I've not had it happen in a shop, but I've heard from theater lighting guys that it can cause problems with cameras, when the light goes into thermal management mode, and some even make smoke hard to see correctly, and it messes with your depth perception as each eye starts trying to focus independently. Not great for either production speed or safety
 
If you are shopping for LEDs & have a superphone with highspeed video, that can be used as a "flicker detector".
Video the illuminated bulb for a few moments & you will see flicker during playback.

LEDs running on DC wont flicker.
 
" .....LEDs running on DC wont flicker.."

Well, yes and no. They all run on DC. The transformer circuit is in the bulb. It converts the AC sine wave into a DC pulse wave. It is the degree of regulation and filtering of the output wave that determines if there is flicker. A square wave output effectively turns the light on and off 60 times a minute. With the proper conversion circuit, large enough capacitors, and a good filter circuit, this is reduced to nearly a flat DC output.

The only way to eliminate this completely is to run the LED on a 12V battery/solar system which does not use any AC at all.
 
Alot of cheap LEDs luminaires dont use rectifier at all. Simply AC of correct voltage applied illuminates at 50 or 60Hz what flickers too fast to notice if everything illuminated and the viewer remains reasonably stationary.

Another "test" for better quality luminaires. If when switched off, they remain slightly glowing a few seconds. This power comes from their filter capacitors discharging. An indication of a well filtered very flat DC voltage for steady, non flickering light.

Btw, "DC pulse wave" is a form of alternating current too.
 
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I use one "daylight" bulb and one warmer bulb in each of my fixtures. I have found that I get better color rendition but it also doesn't wear my eyes out as much as two daylight bulbs. It seems to work at the grinder and at the desk equally.
 
Getting ready to order a bunch of 8ft and 4ft bulbs to get rid of flickering and buzzing in the shop. I noticed nost of the 8ft in 5k are sold out. Would that be because they are more popular or is everything moving to 6k? Ceilings are just under 12 ft.

Thanks
 
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