A good light bulb wattage for reading part 1

Introduction

This article looks at what is a good light bulb wattage for reading and is part 1.

When I was writing this article there was an awful lot of information to consider, so for ease of reading I have split it up into 2 parts. This is the first part. The second part is here.

Do you find yourself sitting down at the end of a long day, in your favorite chair, with the reading lamp turned on, enjoying a good book, but then your eyes feel tired and it becomes hard to read? If so they you are experiencing eye fatigue which could well be caused by not having enough light.

When we were children our parents warned us that if we read in poor light we would damage our eyesight and need glasses or worse. However recent studies have shown that this is not true. Reading under poor lighting will not actually damage your eyesight. What it does do, however, is cause eye strain and fatigue. It also mean we read at a slower pace which may explains why I have been reading that 1,000 page doorstop of a novel for the last three months.

Why is it a problem to read in low light

Firstly, in order to focus on text the iris and the muscles that control the shape of the lens have to contract so that the focused image stays on the retina. However when light levels are low the iris naturally wants to relax to allow in the maximum amount of light.

Additional when the page is poorly lit our eyes have to work harder to distinguish between the writing itself and the background page. The low light levels not producing enough contrast between the two.

Correct lighting is particularly important for those of us who are getting older. The eye needs 1% more light per year to read comfortably, so whilst we were OK reading under the covers with our torch as a kid we now need a lot more light.

Signs of eye fatigue

There are a number of symptoms of eye fatigue to watch out for, including:

• Redness around the eyes
• Squinting
• Headache
• Pain in the brow
• A feeling of burning or itching in the eyes
• Watery or dry eyes
• Blurred or double vision
• Pain in the neck, shoulders, or back
• Increased sensitivity to light
• Difficulty concentrating
• Trouble focusing
• A Feeling that you cannot keep your eyes open.

Ensuring that you have enough light

When considering what is a good light bulb wattage for reading (part 1) we need to think about the light in our houses.

There is little information available on what lighting we should have in our home. No one comes round my living room with a light meter and checks that there is adequate lighting. However, there are levels and checks in place for our offices and workplaces and these can be used as a guide as to what we should be doing in our houses.

The Illuminating Engineers Society has the following guidelines for common office tasks:

As can be seen these guidelines refer to a measurement in lux.

So what is lux?

Lux is a measure of the illumination of a surface, how much light hitting it is being reflected back to our eyes. It is this reflected light that we use for reading. If you have ever seen a professional photographer at a wedding waving around a light meter this is what they are measuring.

For light bulbs we normally see a rating in watts, with the standards being 60W or 100W bulbs (the W stands for Watts). This is the power that the bulb consumers, how much electricity it uses. Normally the packaging will also give a figure in lumens. Lumens is a how much light the bulb gives off. As light bulbs have become more efficient we now have lower wattage bulbs that give off the same amount of light as older less efficient one. So an old 60W incandescent bulb might provide 615 lumens and a new efficient LED 9 watt bulb (which the maker says is equivalent to an old 60W bulb) provided 760 lumens. As we can see there is no longer a straight connection between wattage and the light that is given off.

Measuring Lux

Moreover once we have read the packaging and figured out the lumens we then need to estimate what the lux might be. One lumen provided one lux per meter squared. This means that if all of the light from our 760 lumen bulb fell on an area of 3 square feet and we put our book in the region our book would be illuminated with 760 lux. Simple.

Light level outside out homes tend to be much higher than inside with electric light. Outside on a dark cloudy day the ambient light is around 1,000 lux. On a sunny day this rises to 10,000 lux for indirect daylight and 100,000 lux for direct daylight. My personal preference is for reading outside with indirect sunlight. In this case the page in my book is getting 10,000 lux.

So what lux do we need for reading?

According to Health and Safety magazine the light level for a normal office is 500 lux. As we saw earlier the Illuminating Engineers Society suggests 200-500 lux for reading documents and newspapers.

Chinese Academics carried out experiments on office lighting levels with two age groups, one around 30 and the other around 60 years old. The 30 year olds preferred a lighting level around 500 lux and the 60 year olds around 1400 lux. Both groups agreed that 300 lux was too low and 2700 was too high.

Looking at these numbers it seems that we should be aiming for at least 500 lux on our reading area, and more if we are getting older. Additionally I downloaded a light meter app for my android app and checked around my apartment. My normal reading spot in our living room, on the end of the sofa near a floor lamp measured 120 lux, whilst the bedroom with its bedside lamps provided a puny 22 lux. I often have tired eyes in the evening and have to stop reading. I had been putting this down to working on the computer a lot, but these low light levels are surely not helping.

Part 2 and Conclusions

As I mentioned in the introduction this is a long topic so the article was split into 2 parts

Part 2 is here and concluded this article about what is a good light bulb wattage for reading (part 1).

Or if you want to jump straight to the conclusion of the article click here.