What are some ergonomics designs for door handles?

The obvious things to think about are the size of the handle and the force needed to operate it.  Ideally, you want a handle size that will be comfortable for people with small and large hands.  When considering force, you should take account of users who might have conditions like arthritis, which can cause reduced strength and dexterity.  Other factors are the location of the handle on the door.  It needs to be at an appropriate height and recognisable as a door handle (obvious you would think but not always the case!).  Is the handle going to be indoors or outside?  Handles outdoors can become very cold or hot, and wet, so the material needs to be thought about.  Are users likely to be wearing gloves?  If so, you will need to allow for increased hand size and reduced ability to grip.  These are some suggestions to get you started.  An important thing with any design is to test it out with a small number of likely users before finalising.  This should reveal any serious problems.

I am designing a stool for my GCSE project and I need to research about ergonomics for a stool or seating. Can you help?

There are three main things you need to consider:
1. Identifying the users of the seating (adults, children, elderly people, other user types) and their particular requirements.
2. Designing the stool/seat to meet these user requirements, in particular taking account of anthropometry (body dimension data).
3. Testing the design.
Identifying the users is important, because you need to design for their particular needs and any information you can gather will be useful - age, gender, physical strength, situations in which the seating will be used, how long they will be sitting, what they will be sitting down to do.
Once you know that, you can start to think about the design, making sure that you take into account as many of the users' needs as possible.  An important area of the design will be the dimensions of the stool/seat.  This will be determined by two things - the size of your users and the dimensions of any other furniture the stool will be used with. For instance, if the stool was to be used in a Chemistry lab, with high working benches, then it would have to be an appropriate height to bring users up to the level of the desk.  Information about people's body size is called anthropometry, and is very important in the design of furniture.  (See the Learning Zone topic on anthropometry).  For seating, dimensions such as knee height and thigh thickness are particularly important. Don't forget other user needs - for instance do they need armrests, is back support important, how much padding is needed etc.
Finally, testing is extremely important. You can test designs at early stages (on paper), before you've gone to the trouble of making the furniture, as well as at a later point, when the chair is made.  Asking a few users what they think of a design on paper is a quick way to keep yourself on track and make sure your design isn't way off the mark.  Things like comfort and dimensions are hard to test without having a physical model though, and these are so important that testing is essential.  Remember to test using real users (who are from the same "population" as your eventual users - adults, children, whatever) and to ask them all the same questions and to get them to test in the same way.  With chairs/stools, it's often important to get users to sit for some time (hours, even) to check for comfort, as chairs which can feel fine at first can become very uncomfortable after a while.

I'm designing a desk and I don't know how to write about the ergonomics for it. Please can you help?

With any piece of furniture, the first questions you need to ask are:
1. Who will the users be? (old, young, nationality, any disabilities, other physical characteristics).
2. What will they use the desk for?
These are both key to ensuring that your design fulfils the needs of the users - which is what ergonomics is all about. If you show you have considered the sort of users you will have, and their likely needs (or uses of the desk) then you are half way there.
The most obvious things to consider from an ergonomics perspective are the dimensions and shape of the desk.  The dimensions will come from appropriate use of anthropometric data. The main considerations are the height of the desk, its front to back depth, and width (particularly if you are considering drawers, which restrict the space for the chair). A point which is easy to overlook incidentally, is the thickness of the desk top.  Usually, it is best to have this as thin as possible, without compromising the strength of the desk.  This is because a thick top can prevent a good seated posture - either people can't get their legs under the desk (think of tables with drawers underneath the table top) or the desk ends up too high, and users can't rest their elbows comfortably on the desk without raising their shoulders. 30mm is usually OK.
The shape of the desk will depend on what it is going to be used for, and whether it is intended to join up with other desks.  You might also like to consider the shape of the room it will eventually be in.  Think of open plan offices for instance, where space is at a premium, and desks are often situated in groups of three or four.  If the desk is intended to house a computer, allow enough space to take the computer, plus some room for ordinary reading and writing.  This is where it becomes important to really understand what the desk will be used for.
Other desk characteristics which are worth considering are things like the surface colour and glossiness.  Generally you want a colour which is not too bright or tiring, and a matt finish to avoid glare from overhead or desk lighting.  You may need to consider where power cables will emerge, and whether people will need power sockets on the desk top (e.g. for plugging in a mobile phone charger).
Finally, to be really thorough, you might like to consider the people who have to construct the desk, and move it about.  Will it be too heavy to move - could it be taken apart easily and re-assembled somewhere else - will the instructions be clear - is there an easy place to get a grip when moving the desk...?

Can you tell me how to apply ergonomics to computers?

Computers and computing devices are available to help us in many parts of our lives so your question is difficult to answer briefly. It is best to give some examples of everyday use of computers and see what ergonomists have done to help.
Two of the most common uses of computers that you have probably encountered are for games machines and internet access.
The manufacturers of games machines have tended to be very careful in their designs as they know that the players will have no training, and will want to have an enjoyable game. They have taken an ergonomics approach to design. They put instructions on the screen and provide the player with scores on completion so that they can improve performance and compare their results with others. The controls are designed to match players’ hand sizes, and work in the way that people are used to.
Internet software has generally been designed to be highly ‘usable’.  Microsoft in particular has always been very careful to ensure that all their products have a common ‘look and feel’. This means that every Microsoft product that you encounter will be based on the same set of principles for the way that it appears and the way that it is controlled. For example, most applications will have a box towards the top right hand corner with a cross in it. It always appears there, and when you click on it, the window you are using, closes. The development of usability concepts and the application of principles for ‘look and feel’ are an important component within ergonomics.
In general, there have been 4 main areas where ergonomics have contributed to the development of computers within man-machine systems. It is always important to consider the person and the computer to be a total system where both parts have to be matched. The person is matched to the machine by training and instruction, while the machine is matched to the person by design. The person has to be trained to understand what the computer is for, and how it can be used. This may be relatively easy for young people with some types of games machines which have magazines and other instructional materials, but many older people find computer use daunting as they feel that they have little support, and the machines and the language are unfamiliar. The design of displays and controls is important work for many ergonomists. Not only are there machines for leisure purposes, but also control rooms for chemical plants, police forces and ambulances. Central heating and ventilation will be controlled by computers from a central location within a building. These need to be easily controlled to reduce operating costs and aid maintenance.
Computers are often designed as part of  a suite of furniture. For example, I am sitting at a desk writing to you and the height of the desk, the positioning of the chair and the location of the phone will all need to be considered by ergonomists. This is to ensure that I am comfortable throughout my working day – I will also need to take breaks to ensure that my eyes and limbs are rested. In control rooms you may need to take account of the location of one person with respect to another to ensure that groups can work co-operatively.
The fourth general important area is automation and robots. Computers are used to work on routine tasks that humans don't want to carry out for reasons of cost or danger. This might be in a factory or nuclear plant. In these cases ergonomists help design the means by which the automation works so that control can be safe, cheap and effective. This is important for if the automation fails then there can be accidents. 

Please can you explain to me how I can use ergonomics when designing toys.

The main point of ergonomics is that items should be designed with the users in mind. In this case you need to consider the needs of the child, and possibly the parents or carers. Anthropometry will be important, and so will other things such as safety, and making sure the toy is both appealing to the child and aimed appropriately at its age group. You might want to start by thinking of the various requirements that the child and parents/carers might have for the toy, which would lead to a useful checklist while you are designing. Remember that the psychological /perceptual needs of the very young are quite different from those of older children. If you include text on a toy for instance, you should probably make it lower case, since this is what they are used to (and lower case has the advantage of being generally easier and quicker to read). Parents will have quite different needs of course – they might want a toy made from a "wipe down" material, or a quiet toy as opposed to a noisy one.
In terms of anthropometry, you will need to consider various body dimensions, depending on the sort of toy. Almost certainly you will want to include hand dimensions, since children will probably be handling the toy and you will want to make knobs, dials, handles etc, an appropriate size for the age group you are targeting. Remember that although very young children’s hands are small, their motor control and dexterity may not be all that well developed, so making things too small could be a mistake. I’m no great expert, but I guess that by the time they are 4 or 5 they can deal with small, fiddly things, but not much before then (a quick look through a big toy shop should give quite a bit of information on this as the packaging shows the target age group, usually). You might also want to bear in mind that adults will also interact with the toy, particularly if it is educational, so the dimensions of controls etc, can’t be too small or they will not be able to use them. Other anthropometric dimensions might be needed to determine the size or height of a toy. These could depend on things like eye height and reach (shoulder to knuckle length). You might also need to consider physical strength at various ages – this could be useful to understand what forces the toy will need to withstand during rough play.
Don’t forget to test your designs on children/parents if you can. No amount of preparation beats the information you will get from testing.

What are the anthropometric data and ergonomics in relation to cot design?

There seems to be a gradual increase in body dimensions as each decade goes by; for example, there seems to be about a 10 mm increase in adult stature for each decade.  This may not apply to babies, but it is something of which to be aware.
Babies of different ethnic origin, and fed according to different nutritional beliefs, and dependent on different food availability, may well have measurable differences in their anthropometry.  You may have to take this into account as well.
Beware of the fallacy of thinking that if a baby is of 'average' height (50th percentile), for example, then all the baby's other dimensions will be 50th percentile as well.  This is never the case; nobody is on exactly the same percentile for all body dimensions. Nor should you design for the 'average' person; you should be aiming to accommodate at least 90% of the population.  In other words, your design needs to be suitable for a given envelope of people, for instance from the 5th percentile in stature to the 95th percentile.
You may need to change your criterion for different aspects of the design; for instance, if you think about mums leaning over the edge of the cot, you might like to fix the height of the side of the cot at the 5th percentile of waist height, to be reasonably sure that 95% of mums won't have a problem leaning in to attend to the baby.
You might like to check your design requirements and criteria first - legal issues (especially to do with safety and fire), and the standards created by the BSI, CEN and ISO.
Then ask yourself 3 questions: 'Who are the users?' (babies, mums, others?);  'What will they use it for?' (baby playing, baby sleeping, sick baby, travel cot, etc.); and 'What are the usability requirements arising from these?' (portability, safety, ease of cleaning, comfort, etc.).  You will get your best answers by talking to mums. Then you have a basis for doing the design. Note that people are notoriously bad at telling you what they want; they are much better at telling you what they have got already. You have to listen very carefully to find out what they really want. Also, watch mums doing jobs with cots, and around cots.  This will give you some ideas as well.
When you think you have some new design ideas, try them out as soon as possible.  This is when you may well get some good feedback from mums, because they are faced with something new, and this can prompt some really useful comments from them.  Then try the new ideas out.  This approach is called 'Rapid Prototyping', and it works very well.

When should a display "flash" and when should it "beep"?

Either will help attract the attention of the user, in a way that a steady light does not do well.  However, the question must consider the location of the user, the environment and, of course, the effectiveness of their senses.  To see a light you must look towards it (or a reflection of it) while a sound can attract your attention whichever way you are looking. Thus audible bells/horns are commonly used for fire alarms but would they be effective in a very noisy environment or when people are deaf or wearing ear muffs?  Perhaps it would be best for the display to both "flash" and "beep"?

I am designing a light fitting to fit in an office ceiling, what factors should I consider?

Wow; what a large topic!  With a general question like this I can only offer general advice but am happy to help further when your design becomes more refined.
What light source are you proposing?  Fluorescent tubes, for example, come in standard sizes and with specific light outputs (both colour and quantity.)
I am sure that you will be able to discover what is available by searching the web and investigating the sites of some manufacturers.  The Chartered Institute of Building Service Engineers (CIBSE) also has a useful web site with lots of general information on it (go there).
Some factors for you to consider:
How long should the light source last before it needs to be replaced? Will this be easy and cheap?  You might see MIBF (mean time between failure) quoted.
Will your design trap dirt/be easy to clean (dirty fittings don't, of course, give out as much light as clean ones!)
Don't just think about the quantity of light produced but also the
direction in which is travelling - not only does the direction of the light influence how things look but also can be a major cause of discomfort glare. (I expect you have noticed this problem - as disrupting reflections - on some computer screens.)  Thus, as you may be aware from physics/maths; light is a vector quantity, it has both magnitude and direction.
Any green issues?