LDs... some wavelength science please?

[curtis73]

I'm in the process of buying a bunch of LED bulbs for my backstage run/work lights. I'm tired of blown blue bulbs and hot aluminum clamp lights.

Before I do that, it made me wonder. I understand that the blue light is preferred because of its short wavelength and therefore any light bleed is less likely to be perceived by audience. One of my LDs insists that it doesn't matter what color it is as long as it's not white. He actually prefers green, but that is right in the middle of the visible spectrum which makes me think he's full of s#!t.

Debate? Thoughts? Anyone know a good wavelength to choose for backstage lighting?

 

[BillConnerFASTC]

I like red for not disturbing low light or night vision, but blue seems ever popular. I've taken to using Ketra lamps for running lights - which are RGB and mesh network controlled. With them, you can have any color you want. Easy to leave initial config with buttons for red, green, blue, and there ever popular white.

 

[JD]

The human eye is most sensitive to green, so red and blue is often used.

 

[Malabaristo]

If you're arguing from a physics and human-eye perception standpoint then red makes the most sense for the reason Bill mentioned. If you're arguing from a psychology standpoint, then blue makes more sense: red is an "alarm" color, and more likely to be noticed. Dim blue light is something we've been trained to interpret (by theatre and TV) as darkness, so it's less likely to draw attention. Of course, if you have good masking and are placing the lights to avoid any spill, then color really doesn't matter much. Green is still a weird choice from an aesthetic standpoint... I'd probably choose dim white over green if those were my only options.

Oh, and another thing to consider: many blue LEDs are close enough to UV to cause some fluorescence. This is good for making spike and glow tape visible, but not so good if there are any fluorescent costume/prop/scenery colors involved. Choosing a longer wavelength blue can help reduce that effect.

I have a few of these around to use as runlights: https://www.amazon.com/dp/B06XJ2CKJ6/?tag=controlbooth-20 (though they were slightly cheaper when I bought them.) They remember the last setting through power loss, so they're pretty easy to manage. Not a lot of dimming range, so they may be too bright for some applications. In order to satisfy everyone's color preferences, the rainbow fade setting is obviously the best choice.

 

[curtis73]

Those look like great lights, but I am in a 50x60 black box. I usually use about three incandescent 15w bulbs, so 15w of LED might be a bit excessive... even dimmed.

The other house is a large proscenium, and even there I use 15w tungsten because too much can spill in on the legs. I was thinking some dimmable 5w LED bulbs with RGB (and maybe UV or close to it). That way I can adjust the color to suit. UV in hidden spots to highlight spike and glow, blue in others that might have light spill.

The latest set I did at the proscenium I specifically did "black light" bulbs in the first floor of the house since it had no bleed, but needed to highlight the glow tape so actors didn't die.

 

[seanandkate]

The light receptors in the eye are made up of cones and rods--the cones interpret bright light, and are most sensitive to the green / yellow part of the spectrum. This is why we interpret the sun as "yellow." The rods are responsible for low-light vision, and are more sensitive to the blue / violet part of the spectrum. This is why we interpret the night time as "blue." Now, the rods use a chemical called "visual purple" which will break down in bright light. This is why you can't see anything when you walk from a bright space to a dim one. Your rods need time to regenerate and replace the visual purple. This is also why red preserves your night vision--rods don't process that part of the spectrum.

Back to your question: biologically, I suppose green tries to tread the spectral middle ground, but if it's as dim as worklights should be, your rods probably don't contribute that much to the effort, but you might be less blind if you transition from bright to dark. If you are putting worklights out primarily for your crew who are creatures of darkness by nature, then you are probably best using blue.

 

[macsound]

Also, fwiw, I prefer regular light bulbs (no color LED or CFL) with blue gel. Then you can decide if the area you're lighting warrants R60 or R83 or any other color choice.

 

[techieman33]

I prefer blue over red because it tends to disappear on black surfaces, especially soft goods. A lot of black fabric starts with a red base and when you hit it with red light that helps to reflect a lot more than the blue that just gets absorbed.

 

[JonCarter]

We used to use 25 W 230 V lamps in the 115 V work lights strings behind the sets--pin sockets on a couple pieces of 12TW stranded. Make up as needed and run where necessary.

 

[robmerow]

We use these - you can get them for pennies on Ebay. Very flexible for booth and backstage lighting.

 

[EdSavoie]

I'd go with blue over red, blue being a much more "subtle" colour seems to draw the eye much less than red light leaking through.

 

[TheaterEd]

The following is an image and text that are pulled from an ETC lesson on color theory

"You are probably already familiar with this corresponding graph dating from 1924 - the CIE 1924 Luminosity function diagram. It is commonly referred to as the Photopic Curve. While more modern research shows that it is not a perfect representation; it is still a useful a start to understanding our eye’s reaction to color. The most important point is that our eyes are far more sensitive to colors in the middle of the spectrum than on either end."

As you can see blue ends much earlier than red begins. Meaning, that once you've adjusted to blue, you eyes are still much less 'activated' than if you were adjusted to red.
One more image from their presentation looks at how the different cone cells react to light.

As you see 'red' is more visible because two different types of cone cells are reacting to it. But 'dark blue' only really triggers the blue cone cells. This means that when your eyes have adjusted to blue, when they do see green through red colors (aka spike marks) they will stand out even more.

This is definitely a simplified way of understanding a complex topic, but it works for me. If I've worded anything awkwardly, or misinterpreted something, please let me know.

 

[JD]

Oh, and another thing to consider: many blue LEDs are close enough to UV to cause some fluorescence. This is good for making spike and glow tape visible, but not so good if there are any fluorescent costume/prop/scenery colors involved. Choosing a longer wavelength blue can help reduce that effect.

Bingo!
I like blue and have a bunch of the old blue CFLs. Some blue LEDs are the same way. Swear by them as they do tend to cause markers and other objects to stand out and in some cases fluoresce.