Green, Red, Blue or some other colour?

[Zen_seeker]

Since I was a kid I was always told a green light was good to see in a green house or nursery and red lights where for dark rooms and photography.

Recently I started looking to see which was the right or best choice for an off the shelf, found in any hardware store, standard lightbulb that would go in a typical light housing.

What I found with some online reading and AI questions was that red was the best choice.

When I pressed and questioned the AI based on what I had read this was the reply:

“Most red LED bulbs sold for colored decorative use emit in the 620–660 nm range, which is the plant-safe band for night lighting.

To be certain:
- Check packaging/specs for a listed wavelength or spectral power distribution (SPD). Safe range: ~620–660 nm.

- If only a color name is given, "red" decorative LEDs almost always center in that range.

- Avoid bulbs that list "warm white," "amber," or give a correlated color temperature instead of a true color — those can include other wavelengths.

- If you want exact confirmation: use a handheld spectrometer or a smartphone spectrometer clip to read the peak wavelength (not usually necessary for typical red decorative bulbs).

- Practical test: place the bulb near a plant during its dark period for a few nights; if flowering/photoperiod responses continue unchanged, the light level/wavelength is likely acceptable (this is a conservative check for sensitive species).

Summary: a plain red LED bulb from a retailer is very likely in the safe 620–660 nm band; only get worried if the manufacturer lists mixed/white spectra or gives a blue/green component.”

After some more back and forth and looking on the internet I asked the AI this: “”Why is it I find this when you say red? “Growers often use green light during the dark cycle because it is less likely to disturb the plants' flowering process. This is due to plants being less sensitive to green light compared to blue or red light, making it a safer option for visibility without disrupting their growth.””

AI answered: “Both statements are true in different contexts.

- Sensitivity: plants are generally less sensitive to green than to blue for cryptochrome/phototropin responses, and phytochrome action is strongest in red/far‑red—so green can be less disruptive than bright blue or broad‑spectrum white for some species and uses.

- Caveat 1 — Perception and penetration: green penetrates leaf tissue well and can still trigger or modulate photoreceptor signaling (including cryptochromes and phytochromes indirectly), so it is not inert. At moderate or high intensities green can alter circadian/photoperiod signals or physiological responses.

- Caveat 2 — Species & sensitivity: some photoperiod‑sensitive species or highly sensitive cultivars can have their flowering or night signaling affected by even low levels of green light.

- Practical rule: for simple human visibility during a plant dark period, many growers use dim green safely; for strict photoperiod control (flowering, experiments, very sensitive plants) dim red (620–660 nm) is the safer choice because red is less likely to activate blue‑sensitive pathways and is well characterized for minimal night disruption.

So the quoted guidance reflects a pragmatic tradeoff (green is often acceptable for visibility), but red is more conservative and more reliably safe for strict dark‑period control.”

So I’m trying the red LED bulbs. They are enough to see by but noticeably darker.





Anyone try anything other than green to see by in dark mode?

What were your results?

 

[Pipecarver]

Since I was a kid I was always told a green light was good to see in a green house or nursery and red lights where for dark rooms and photography.

Recently I started looking to see which was the right or best choice for an off the shelf, found in any hardware store, standard lightbulb that would go in a typical light housing.

What I found with some online reading and AI questions was that red was the best choice.

When I pressed and questioned the AI based on what I had read this was the reply:

“Most red LED bulbs sold for colored decorative use emit in the 620–660 nm range, which is the plant-safe band for night lighting.

To be certain:
- Check packaging/specs for a listed wavelength or spectral power distribution (SPD). Safe range: ~620–660 nm.

- If only a color name is given, "red" decorative LEDs almost always center in that range.

- Avoid bulbs that list "warm white," "amber," or give a correlated color temperature instead of a true color — those can include other wavelengths.

- If you want exact confirmation: use a handheld spectrometer or a smartphone spectrometer clip to read the peak wavelength (not usually necessary for typical red decorative bulbs).

- Practical test: place the bulb near a plant during its dark period for a few nights; if flowering/photoperiod responses continue unchanged, the light level/wavelength is likely acceptable (this is a conservative check for sensitive species).

Summary: a plain red LED bulb from a retailer is very likely in the safe 620–660 nm band; only get worried if the manufacturer lists mixed/white spectra or gives a blue/green component.”

After some more back and forth and looking on the internet I asked the AI this: “”Why is it I find this when you say red? “Growers often use green light during the dark cycle because it is less likely to disturb the plants' flowering process. This is due to plants being less sensitive to green light compared to blue or red light, making it a safer option for visibility without disrupting their growth.””

AI answered: “Both statements are true in different contexts.

- Sensitivity: plants are generally less sensitive to green than to blue for cryptochrome/phototropin responses, and phytochrome action is strongest in red/far‑red—so green can be less disruptive than bright blue or broad‑spectrum white for some species and uses.

- Caveat 1 — Perception and penetration: green penetrates leaf tissue well and can still trigger or modulate photoreceptor signaling (including cryptochromes and phytochromes indirectly), so it is not inert. At moderate or high intensities green can alter circadian/photoperiod signals or physiological responses.

- Caveat 2 — Species & sensitivity: some photoperiod‑sensitive species or highly sensitive cultivars can have their flowering or night signaling affected by even low levels of green light.

- Practical rule: for simple human visibility during a plant dark period, many growers use dim green safely; for strict photoperiod control (flowering, experiments, very sensitive plants) dim red (620–660 nm) is the safer choice because red is less likely to activate blue‑sensitive pathways and is well characterized for minimal night disruption.

So the quoted guidance reflects a pragmatic tradeoff (green is often acceptable for visibility), but red is more conservative and more reliably safe for strict dark‑period control.”

So I’m trying the red LED bulbs. They are enough to see by but noticeably darker.

View attachment 128422

View attachment 128421

Anyone try anything other than green to see by in dark mode?

What were your results?

I don't check my plants during lights out, I'm not awake then. My pants are timed for me 8 pm or 9pm depending on daylight savings lights out is the only constant. I don't think any light is safe through lights out period in flower but I thought green was the go to for short periods. I have a small green flash light that was supposed to be plant safe..Dr. Bugby said if its bright enough to read print its too bright and green is bright so??????

I just extend their day by 10 min with far reds to give me the effect I want, Green is said to penetrate the leaves better and to enhance the other spectrum's during lights on. I'm just playing with the Blue 450nm lights and I like what they did in veg by keeping the plant short and stocky, when I shut them off and topped them the whole plants arms/branches rose to the top giving me far more bud sites on top than a single topping usually does.

 

[BackyardBoogie]

Ive been using green lights for a very long time in my work space around tents/grow rooms and never had any problems. But you may want to be careful with the red spectrum, that can make the plants think its day time.

Dr. Bugby said if its bright enough to read print its too bright and green is bright so??????

I gotta respectfully disagree with that one. Ive ran greenies with minimal lighting to keep stuff in veg. If the plants cast a shadow with a regular spectrum bulb, its enough to keep them in veg. Even if its just for 15 minutes in the middle of the dark cycle. The old Santa Cruz mountain growers called it tiki torch veg.

 

[Pipecarver]

Ive been using green lights for a very long time in my work space around tents/grow rooms and never had any problems. But you may want to be careful with the red spectrum, that can make the plants think its day time.


I gotta respectfully disagree with that one. Ive ran greenies with minimal lighting to keep stuff in veg. If the plants cast a shadow with a regular spectrum bulb, its enough to keep them in veg. Even if its just for 15 minutes in the middle of the dark cycle. The old Santa Cruz mountain growers called it tiki torch veg.

In flower....in veg it doesn't matter, you can run in veg 24 hr light cycles or what ever you want but if you start adding lights on in flower during 12/12 lights out cycle you can stress your plants to produce hermies...its then Dr.BB said light interruption cause issues...not in veg

 

[Zen_seeker]

@Pipecarver it’s funny you mention Dr BB as he’s one of the references in the pages I’ve been reading. I had to go back and search the article to be sure. Also found a good scientific study on red, green and blue light you might like, I’ll post the link in your thread.



I did further searching today and green is always the old standby but newer studies and internet seem to think standard red LEDs in the 620+ range can be better especially in flower…

As my grow room is also a hall with daily traffic and lights are occasionally needed I’m looking for the best solution. The same bulb in green is what I was using up until yesterday.

AI response to questions:

Use the dim red bulb.

Reasoning (concise):

- Red (620–660 nm) is the most conservative choice for preserving a strict dark period because it minimally activates the blue/UV-sensitive photoreceptors and the phytochrome-mediated night/dawn signaling that trigger flowering responses.

- Green is lower-risk than white/blue for brief inspections, but it can still be absorbed and affect plant signalling more than red in some cases.

- Keep the exposure very short (<30 seconds), use low intensity, and avoid repeated or long inspections during the first one to three weeks of the 12/12 transition when the plant is most sensitive.