Understanding sunlight

By Nathan Burton

August 2026

Light is energy traveling in waves. The distance between those waves changes how that energy behaves when it reaches a reptile, from starting vitamin D3 production in the skin to warming tissue beneath the surface. Human eyes see a narrow slice of that energy, while many reptiles also see wavelengths hidden beyond the violet edge of our vision. Together, these wavelengths form a spectrum that shapes both the animal and the world around it.

The solar spectrum

Sunlight reaches the ground as one continuous spread of wavelengths. We give sections of it different names because each interacts with the body in a different way. The deep dips in the curve show wavelengths absorbed by water vapor and other parts of the atmosphere before the light reaches us.

UVC + non-terrestrial UVB

below 290 nm

UVC sits below 280 nm. The atmosphere absorbs these wavelengths before they reach the ground, so no creature on Earth has evolved to use them. UVC is hazardous to all life on Earth, which is why it is used in medical sterilization. The next 10 nm are technically UVB, but the atmosphere absorbs them as well, so researchers often group both bands together as dangerous, non-terrestrial wavelengths.

In the enclosure There should be no output in this band. Some poorly designed or faulty reptile lamps have been found to emit UVC or very short-wavelength UVB, which can cause severe eye inflammation, burns and death. A lamp can produce a reasonable UVI while still having an unsafe spectrum, which is why UVB lamps need independent spectral testing.

Seeing UVA1

Human color vision is built from red, green and blue. Cone cells in our eyes measure the strength of each, and the brain compares those signals to build every color we see. When all three are in balance, light appears white. Plant lights that combine red and blue with very little green appear bright pink because one part of that balance is missing.

Many reptiles can see a fourth color called UVA1 that is invisible to us. Without that color, light that appears white to us will look tinted to them. Lizards, snakes and turtles can all generally see UVA1.

These simplified curves compare the overlapping cone sensitivities involved in color vision. Exact sensitivities vary by species. Many reptiles can see UVA1 to the left of the human visible range.

A computer screen creates every color from red, green and blue, so it cannot display UVA1 or reproduce the colors a reptile actually sees. This simulation uses ordinary color mixing to show how the balance changes when UVA1 is missing. The planner identifies which lamps include UVA1.

Color balance

Add red, green and blue until the enclosure looks balanced to you. Then switch to the reptile's view and add UVA1.

No colors have been added.

The solar spectrum

Seeing UVA1

Color balance

References