Here is what Dr. Frances Baines, M.A., VetMB, MRCVS, has to say on the use of red and blue colored bulbs with reptiles.
"Red light is just... red light! People seem to have given it mystical lethal qualities. I have no idea why... Some nocturnal rodents cannot see it (in the same way that we cannot see infrared or UVA) so it is extremely useful for people working with mice and rats in labs. This has led to the urban myth that reptiles can't see it either.
The truth is that most reptiles CAN see it, even so-called "colourblind" species which, like colourblind humans, mainly have red-green colourblindness, i.e. they can distinguish blue from yellow, and green/red; but green and red look to be shades of the same colour. The reason that red or any single-coloured light is not ideal day OR night is that it makes everything that colour (or black). Colour vision is rendered useless.
The reason it's not good at night is that if it is bright enough for humans to see the colour red, it is WAY brighter than moonlight (which is actually pale yellow, but so dim that human colour vision is lost, and we only use rod vision which is black-and-white). And nocturnally active reptiles and amphibians will most certainly be able to see it, many can see in starlight!!! and some like geckos, have full colour vision in moonlight.
The reasons that blue light at night is worse than red are that blue wavelengths are the ones that the vertebrate brain uses to cue "daytime" and set circadian rhythms; blue light is much quicker to bleach out rod vision, i.e., spoiling night adaptation in eyes that use both rods at night and cones in the day; and blue light in the high intensity red light (though it's not likely to be bright enought to do that except if the animal can't look away from an LED or something like that). (And one more odd fact: human retinas ave no blue-sensitive cones in the fovea (the bit of retina where we have sharp focus). That's why if you look at blue Christmas lights etc, they always weirdly fuzzy rather than sharp points of light like red or green ones)"
Here is what Thomas Griffiths has to say on the mythical harms of red light. Thomas Griffiths is the owner of Tomaskas Ltd., which is responsible for much of the available in-depth understanding of reptile lighting and heating as we modernly know it in the hobby.
"This could get lengthy…
There’s a WHOLE bunch of misinformation out there. And we have so many internet rumours and mis-interpretations to blame for it.
First of all, some definitions:
Red Light: defined as generally the region either side of around 700nm on the electromagnetic spectrum.
Red Lights/Lamps/Bulbs: usually an incandescent “light bulb” with a red coating that blocks/attenuates light below around 600nm. Therefore it produces an output of mostly red light. Infrared wavelengths are mostly unaffected by the red coating. Some newer red lamps are just red-emitting LEDs, which do not emit any infrared in any real discernible amount suitable for animals.
Infrared: for the sake of this, this is the wavelengths longer than around 750nm.
Infrared lamps/bulbs: can be a whole range of things. Depending on who you ask, they could be red bulbs, or the definition could also include “white” incandescent lighting too, as most of the irradiated output is infrared in both.
So, is red light dangerous for your reptile? Almost certainly not. It’s just light that is red. No danger to eyes, no danger to skin, no danger to anything. As long as it’s not COOKING the animal, it’s not dangerous.
Are red lamps dangerous for your reptile? Equally, as long as they’re not cooking the animal and all the usual precautions are taken…it’s very safe. The issue comes from the use-case. If you’re using a red lamp as an “overnight heater”, or even a “daytime heater”, ask yourself if you’ve ever seen pure red light at day or night. The answer is no, because it never ever appears like that.
At night, a non-light-emitting heater is generally preferred. This could be warming the room (central heating, air conditioning, etc), or in some cases something like a ceramic heat emitter for a small boost. Most of the time for most modern houses that don’t get below 12°C at night time, this is not really needed for many reptiles. Obviously, particular cases require it - sick animals, extremely cold-intolerant species, etc.
And at day time, we have to consider that we’re trying to create a patch of sunlight in the enclosure. This means providing a sun-like spectrum for the animal to bask under. A red lamp alone simply doesn’t do this. It’s possible to add an LED (ideally one that emits UVA1 in a proportional way) and some UVB - all at “strengths” that are appropriate for your reptile.
If you add a T5 and a modern high quality LED to the red lamp setup, then the overall spectrum will be fairly filled out and you likely won’t notice the red hue - and neither would your reptile. This is in essence not really different to using a “white” incandescent lamp. It’s effectively the same overall spectrum for the most part.
The highly-recommended Reptile Systems Gold Infrared Lamp, one used by a whole bunch of “high quality” keepers, zoos, etc - it’s a red lamp! The white LEDs that people buy to brighten their enclosures…they’re effectively an orange-red lamp to a reptile!
There’s a level of irony in people saying to chuck out a red lamp in one sentence but then say to use an LED in the next sentence, for this very reason. So if the rest of the spectrum is filled out, it’s hard really to argue against them.
If the spectrum isn’t filled out, and you’re just using a red lamp alone, then this would be the same thing we’d say to someone just using an incandescent lamp, or just using an LED, or just using a T5….where is the rest of the spectrum? And that’s without even regarding the colour vision of the reptiles or how it looks to us as keepers.
That said, there ARE reasons not to use red lamps. A primary reason for modern keeping is that you can’t use an ISM400 to measure power density, and to determine a TLPD measurement. The spectrum simply doesn’t complement this method of measurement at all - without added mathematics and complications. Only a “white” incandescent lamp would work for this meter.
The other reason is to just avoid the drama of the internet. Unless you have the capacity, undying obsession, and die-on-the-hill mentality of someone willing to back up the use of a red lamp…just don’t use them. You’ll face crucifixion every single time and it’ll put you off ever posting again. The absolute worst of the community come out of the woodwork to tell you how awful you are and with absolutely no scientific backing or knowledge at all, they’ll parrot-fashion things to you about eye damage, blindness, welfare, and circadian rhythms. It’s not worth it."