Background: There is a zone of the atmosphere in which ozone absorbs some 98% of non-ionizing but dangerous UV-C and UV-B. This so-called ozone layer starts at about 20 miles (32 km) and extends upward. Some of the ultraviolet spectrum that does reach the ground (the part that begins above energies of 3.1 eV, a wavelength less than 400 nm) is non-ionizing, but is still biologically hazardous due to the ability of single photons of this energy to cause electronic excitation in biological molecules, and thus damage them by means of unwanted reactions. An example is the formation of pyrimidine dimers in DNA, which begins at wavelengths below 365 nm (3.4 eV), which is well below ionization energy. This property gives the ultraviolet spectrum some of the dangers of ionizing radiation in biological systems without actual ionization occurring. In contrast, visible light and longer-wavelength electromagnetic radiation, such as infrared, microwaves, and radio waves, consists of photons with too little energy to cause damaging molecular excitation, and thus this radiation is far less hazardous per unit of energy.

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In which case photons would have more energy, spec A or spec B?
Answer: spec A

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In which case photons would have less energy, spec A or spec B?
Answer: spec B

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In spec A, would the photons have less or more energy than in spec B?
Answer: more

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In spec B, would the photons have less or more energy than in spec A?
Answer: less

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: Which radiation would be more hazardous, spec A or spec B?
Answer: spec A

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: Which radiation would be less hazardous, spec A or spec B?
Answer: spec B

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In spec A, would the radiation be less or more hazardous than in spec B?
Answer: more

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In spec B, would the radiation be less or more hazardous than in spec A?
Answer: less

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In which case molecular excitation would be more harmful, spec A or spec B?
Answer: spec A

Situation: John was interested in the Sun's radiations that Earth receives. One of the radiations was in the ultraviolet spectrum. He categorized it as spec A. The other radiation was the visible light. He categorized it as spec B. He then searched online to find the pros and cons of each of them.

Question: In which case molecular excitation would be less harmful, spec A or spec B?
Answer: spec B