Full Spectrum light is a phrase that is used to describe light that mimics natural sunlight as closely as possible. Natural sunlight is a definitive example of a full spectrum light.  Full spectrum light provides a full distribution of all colours that make up the visible light spectrum including various invisible wavelengths needed for a number of biological and psychological processes.

Full spectrum light has a very high CRI (colour rendering index) measuring between 95-100.  CRI is a unit of measure used to assess the ability of a light source to reveal the colours of different objects in comparison to a natural light source.  A high quality full spectrum light will commonly have a colour temperature between 5000k to 6500k which is commonly defined as Daylight.  

Can Light Bulbs Reproduce Full Spectrum Light?

Whilst no bulb can replicate sunlight perfectly, some daylight and fluorescent bulbs can come very close to replicating the same colour of light.  If a light advises it has a high CRI 90 or more and it is a daylight colour this will be as close as you can possibly get.

What Does "Full Spectrum Light Bulb" Mean?

The phrase "full spectrum light bulb" marketing description. It generally refers to any artificial light source that attempts to replicate the light spectrum of natural daylight more closely than typical incandescent or fluorescent lighting.

Standard incandescent bulbs are stronger in the red and yellow parts of the light spectrum but weaker in blue and green which gives them a lower CCT which is called warm white.  Conventional white LEDs or fluorescent tubes can be any colour from warm white to daylight but on average will not produce the same light spectrum as a light that is advised as “full spectrum.”

A bulb labelled as "full spectrum” should have the following attributes:

1. High CRI (90+ or 95+): This is key for accurate colour perception, which is vital for tasks such as art, photography, or reading.  It is also believed to reduce eye strain which makes it even more useful for these tasks.
2. Daylight CCT (5000K–6500K): This colour temperature aims to mimic the bright, white light of the sun at midday.
3. Broader Spectral Coverage: Advanced full spectrum bulbs are designed to fill in the spectral gaps common in standard lighting as much as possible. Some even include carefully controlled, low levels of UVA to further mimic sunlight, but these levels will be tiny compared to natural daylight.

Whilst full spectrum bulbs are designed to emanate natural sunlight as much as possible they do not produce the full range of radiation that sunlight does meaning that they will not be harmful to human eyesight or have adverse effects if you are in prolonged contact with the light.

What Is the Healthiest Light for Your Eyes?

The best light for your eyes would be one that has a high CRI producing as high of a colour spectrum as possible and therefore leads to minimal eye strain.

Light sources with a CRI of 90 or more are healthier as the high CRI allows colours to be perceived more accurately and clearly.  This reduces eye strain and fatigue as less mental effort is needed to focus on seeing what is around you and the task at hand.  If you use a light like this coupled with one that has a colour temperature of 5000k-6500k and one that  has minimal flicker this will be the healthiest light for the daytime.

It is recommended that you shift to a warmer colour light such as 2700-3500k for the evenings as excessive exposure to too much daylight colour is believed to disrupt sleep patterns and circadian rhythms.  If you switch to a warmer colour light in the evenings this should easily be overcome.

To conclude - high-quality full spectrum light bulbs with a high CRI and flicker-free operation are a highly recommended choice for eye health especially when doing something that is visually focused.  They are designed to provide great visual clarity as they mimic the midday sun as closely as possible without the associated risk of too much exposure to UV rays from sunlight.