What are filters for?

[Hallorann]

I recently purchased a Streamlight TL-2 LED as part of the Thunder Ranch package. Included was a green filter that fits over the head of the light.

What is this for? I noticed that other filters are available (blue, red, etc). What do these accomplish other than lowering output and changing the color of the light?

Thanks

Hallorannn

 

[65535]

Red is great for night vision, I read a package saying blue was anti glare, I'm sure a quick serach could pull something up.

 

[Quantumstate]

Marketing balderdash.

Silly party colors.

 

[redskins38]

Blue is good for hunting and locating blood

Red is great for keeping your night vision or when you need to get around without waking someone up

 

[kanarie]

red: for maintaining night vision (sort of)
blue: for tracking game that has been shot in the dark(blood)
IR: for use with infrared googles
pink: becase it is pretty :naughty:

 

[2xTrinity]

Personally I think a better way to implement something like that would be to create an LED with separate red, blue, green, and IR emitters. Then, instead of filtering the output, simply switch on only one color
(or IR only if you need night vision), and save all that power. For white output, switch on RGB together. In most practical lights though, white + red is really the only combination that you'd really need -- red for night vision, and white for general visiblity. A typical white LED (blue + phosphor) and a secondary red would do the job just fine for that.

 

[65535]

Check out the Kroma.

 

[cratz2]

Green seems to be a bit less likely to spook animals. At least whitetail deer. My father in law has a cabin where deer are VERY often within 10-100 yards. We/I look out the windows down the side of the hill. With a white light, they tend to stop and stare at the light. If you keep it still, they'll keep eating or doing whatever they were doing. But if the light moves very much, they bolt. With the green, they pretty much don't even look up at it some times.

My favorite light for such use is a Q3 with a REALLY bright green LED. Not much throw, but on a dark night, it's easily enough to illuminate a deer at 100 yards, even from the side. And when they look right towards you, they look kinda like Paris Hilton trying to keep a guys attention.

In my experience though, filters with LED lights loose a LOT of output... much more so than with incandescents with the same filters.

 

[jsr]

Haha, I posted the same question this morning in the General forum.

I've read the same things about red, green, and blue on what they seem most useful for. However, I have a question about the red: When it's bright (like when attached to a bright LED light or incan), would the amount of light, even though it's red, still blow away your night vision?

I've read articles that state tho red is used often for night vision, a combination of dim white light with a small bit of red is better since the human eyes are more sensitive to a blue-green tint and thus pick up things better.

 

[cratz2]

How I understand it, is if you had a 10 lumen white LED light and a 10 lumen red LED light, the red would still interfere less with your night-adapted eyes than would the white. Because of how the rods and cones process light and colors.

Same would be true when comparing 1 lumen lights or 60 lumen lights... the red still impacts your eyes less than the same measured brightness white light.

Now, as much as I liked my crazy bright Lux III red (and red/orange) light, trust me... it will effect your night-adapted eyes in about a second.

 

[2xTrinity]

I've read the same things about red, green, and blue on what they seem most useful for. However, I have a question about the red: When it's bright (like when attached to a bright LED light or incan), would the amount of light, even though it's red, still blow away your night vision?

I think the issue here is that the cones, which are responsible for daytime vision, have some sensitivity to red -- enough for you to be able to see by it. The rods however for night vision are most sensitive to blue colors and have almost no sensitivity for red -- this means you can use your cones to see with red, and your rods (responsible for night vision) will not be affected at all. This is also why they used red light when developing film -- those lights were quite bright, enough to light up a whole room no problme, but no matter how much light there was, the wavelength is just too long to expose the film at all.

 

[Doug3581]

....I have a question about the red: When it's bright (like when attached to a bright LED light or incan), would the amount of light, even though it's red, still blow away your night vision?....

No, it will not.
~

 

[Sub_Umbra]

...However, I have a question about the red: When it's bright (like when attached to a bright LED light or incan), would the amount of light, even though it's red, still blow away your night vision?...

Yes and no. In a very strict sense if the light is actually red with a longer wavelength that ~640nm -- no. Most "red" lights sold for this purpose are actually in the 625-630nm range which the rods are still sensitive to.

If the wavelength is, in fact longer than 640nm there is a tendancy to have it too bright -- partly because light in that range is so hard to work with and partly because most think that it cannot adversely affect their dark adapted vision. If the red light is too bright it can burn an afterimage into your cones that can completely overwhelm the dim output from your totally unaffected rods.

This is very easy to prove by just shining a 5mm red LED briefly into one of your dark adapted eyes while the other is held closed. After the light is turned off look through one eye at a time while holding the other closed, using first one eye and then the other. You will not see as well with the eye you shined the light into. Even though the red light did not directly impair your dark adapted vision in the exposed eye the afterimage burned into the cones will overwhelm your rods output. Try it.

 

[Pla]

Another point is the quality of the filter.
Regular red filters only reduce blue and green light but not fully eliminate it.
Good red filters will block 100% green and blue.
For that reason red led is better - it doesn't emit green or blue.

You can try putting red filter over blue/green led - you shouldn't see any light if the filter is good.

Or just put the filter over a map or some colorful picture - you should see only red/black shades and no other colors for a good filter.